- Email: [email protected]
Impact of multiple injections on immunization rates among vulnerable children
Impact of Multiple Injections on Immunization Rates Among Vulnerable Children Maureen S. Kolasa, RN, MPH, Timothy J. Petersen, MPH, Edward W. Brink, MD, Igor D. Bulim, BBA, John M. Stevenson, MA, Lance E. Rodewald, MD Background: In 1997, the Advisory Committee on Immunization Practices (ACIP) recommended a switch from oral polio vaccine (OPV) to inactivated polio vaccine (IPV) for the first two infant doses. The ACIP also recommended use of diphtheria, tetanus, and acellular pertussis vaccine (DTaP) for infants. These recommendations resulted in two additional injections at the 2- and 4-month immunization visits. This study evaluates the implementation of new IPV and DTaP immunization recommendations and their impact on immunization coverage levels. Methods:
Immunization coverage was assessed in public clinics in three urban areas before and after the recommendations. One pre- and three post-recommendation cohorts were followed to 12 months of age.
Results:
Almost all (ⱖ88%) infants in the pre-recommendation cohort received OPV, DTP, and only one or two injections. Almost all (ⱖ78%) infants in the post-recommendation cohorts received IPV, DTaP, and three or four injections. The percentage of infants in the post-recommendation cohorts up-to-date for immunizations at 12 months of age was slightly higher than those in the pre-recommendation cohort.
Conclusions: Providers rapidly switched from OPV and DTP to IPV and DTaP. Coverage at 12 months of age was higher among IPV/DTaP recipients than among OPV/DTP recipients. Provider and parent acceptance of four injections at a visit was high. The recent pneumococcal conjugate vaccine recommendations potentially add a fifth injection at 2 and 4 months of age. Acceptance or rejection of five injections by providers and parents needs early assessment. Medical Subject Headings (MeSH): diphtheria–tetanus–pertussis vaccine; immunization; injections; poliovirus vaccine, inactivated (Am J Prev Med 2001;21(4):261–266)
Background
R
ecommendations for routine vaccination against polio, diphtheria, tetanus, and pertussis changed in early 1997, resulting in two additional injections at infant’s 2- and 4-month immunization visits. The Advisory Committee on Immunization Practices (ACIP) recommended a preferred schedule of two doses of inactivated poliovirus vaccine (IPV) at 2 and 4 months of age, followed by two doses of oral poliovirus vaccine (OPV) at 12 to 18 months and 4 to 6 years (the “sequential” schedule) in order to decrease the risk of vaccine-associated paralytic polio (VAPP).1,2 In addition, the ACIP, the American Academy of PediFrom the Immunization Services Division, National Immunization Program, Centers for Disease Control and Prevention, Atlanta, Georgia Address correspondence and reprint requests to: Maureen S. Kolasa, RN, MPH, Centers for Disease Control and Prevention (CDC), National Immunization Program, Immunization Services Division, 1600 Clifton Rd, MS E-61, Atlanta, GA 30333. E-mail: [email protected].
Am J Prev Med 2001;21(4) Published by Elsevier Science Inc.
atrics (AAP), and the American Academy of Family Physicians (AAFP) all recommended use of diphtheria, tetanus, and acellular pertussis (DTaP) instead of diphtheria, tetanus, and pertussis (DTP) because the acellular pertussis vaccine is less likely to cause adverse events.3–5 Polio vaccination recommendations were further revised in 1999 when the ACIP, along with AAP and AAFP, recommended an all-IPV schedule.6 – 8 Immunizations against Haemophilus influenzae-type b (Hib) and hepatitis B (HepB) are also recommended at 2 and 4 months.8 Policymakers and immunization providers were concerned that multiple simultaneous injections could decrease immunization coverage levels.9 –17 They reasoned that some children would be unlikely to make additional visits for any delayed vaccinations because of providers’ or parents’ reluctance to accept up to four simultaneous injections. A decrease in immunization coverage is of particular concern for children in urban low-income communities because children in these areas are already at increased risk for vaccine-prevent-
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able disease outbreaks as was seen during the measles resurgence in the early 1990s.18 –23 Because of this concern and the conflicting opinions and studies on this issue, the Centers for Disease Control and Prevention evaluated the introduction of the sequential poliovirus vaccination schedule and DTaP. The goal of the study was to determine the impact of the sequential schedule of IPV/OPV and the licensing of DTaP for infants on childhood immunization coverage. Specific study objectives were to compare overall and vaccine-specific childhood immunization rates for polio, diphtheria, tetanus, pertussis, Hib, and HepB before and after implementation of the sequential schedule of IPV/OPV, and the licensing of DTaP for children ⬍12 months. The study also examined the time to acceptance of IPV and DTaP and the change in the number of injections given per immunization visit.
Methods This study was set in three geographically diverse cities (Philadelphia, Pennsylvania; Jacksonville, Florida; Milwaukee, Wisconsin) in publicly funded health clinics located in areas at risk for underimmunization. The clinics included public health clinics, federally qualified health centers, and university clinics receiving public funds for infant immunization. The clinics served primarily low-socioeconomic-status clients. The management of all participating clinics adopted policies encouraging, but not requiring, healthcare providers to recommend IPV and DTaP to clinic clients. Using the Clinic Assessment Software Application (CASA),24 immunization coverage levels were assessed before and after each clinic’s adoption of the sequential IPV/OPV schedule and use of DTaP in infants. Age-appropriate immunization coverage was determined in the single pre-recommendation birth cohort and in the three post-recommendation birth cohorts in each clinic and city. Because this is a birth cohort design, the study population was enrolled during “enrollment windows” of sufficient duration to achieve the desired sample size. The target sample size for each cohort in each city was 378, the minimum number that would enable detection of a difference in vaccine coverage between the pre- and post-recommendation cohorts of 10 percentage points with power of 0.8 and ␣ of 0.05. Infants in the pre-recommendation cohort were born March through June 1996 and began their immunizations before the recommendation for use of IPV and DTaP in infants. In post-recommendation cohorts, infants were born as follows: Cohort 1, September–December 1997; Cohort 2, January–May 1998; and Cohort 3, June–August 1998. Infants in the first post-recommendation cohorts were eligible for their first immunizations after participating clinics had adopted a policy for use of the sequential IPV/OPV schedule and DTaP. Infants were eligible for inclusion regardless of whether they entered the participating clinic for their first immunizations or transferred into the clinic at an older age. Immunizations administered in nonparticipating clinics were included in the vaccination history of cohort children and
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were coded as having been administered elsewhere. Race/ ethnicity was recorded if available in the patient chart. Infants were excluded from the study cohorts if they did not receive their first dose of DTP/DTaP, Hib, or polio immunization by age 6 months (180 days) or if they did not receive any routine immunizations (DTP/DTaP, Hib, or polio) by age 12 months in the participating clinic. Infants were also excluded if they had no immunization record or if the immunization record was not clear as to which immunizations were received. For example, if the record was not clear if an infant received IPV or OPV, that infant was excluded. If the record was not clear if an infant received DTP, the DTP–Hib combination vaccine, or DTaP, the infant was also excluded. The primary outcome measures were vaccination status at ages 3, 5, 7, and 12 months. This design included a 30-day grace period after the recommended ages for vaccination of 2, 4, and 6 months. Infants were considered age appropriately up-to-date (UTD) for individual vaccines—DTP/DTaP, Hib, HepB, polio vaccine (IPV or OPV)—if they had received one dose by age 3 months and two doses by age 5 months. At age 7 and 12 months, UTD infants had received three doses of DTP/DTaP along with at least two doses of polio, Hib, and HepB immunizations. Enrolled infants could have one of three dispositions from the cohort at age 12 months: (1) complete immunization series, (2) incomplete immunization series, or (3) lost to follow-up. When the enrolled infants reached age 1 year, attempts were made to contact the parents or guardians of those infants whose record indicated that they were not UTD for their immunizations. Five attempts were made to reach parents by telephone. If unsuccessful, an attempt was made to contact the parents via mail. If reached, parents were requested to provide the names of additional immunization providers for their infant and consent for contact of these providers. Additional immunization providers were then contacted for the infant’s immunization history. Infants UTD for immunizations at age 12 months according to participating clinic information were included in the final analysis. We also included infants not UTD according to participating clinic records, but whose parents were successfully contacted to determine if their infants received immunizations elsewhere. Infants whose immunization records indicated that they were not UTD at age 12 months and whose parents could not be located or who refused to provide information were considered lost to follow-up.
Results Initial enrollment for each cohort ranged from 383 to 489 in Philadelphia, 383 to 524 in Jacksonville, and 371 to 400 in Milwaukee. Final enrollment, after excluding those lost to follow-up, ranged from 350 to 448 in Philadelphia, 285 to 467 in Jacksonville, and 332 to 351 in Milwaukee. The greatest loss occurred in Jacksonville, with 11% lost to follow-up in the pre-recommendation cohort, and 19%, 24%, and 31%, respectively, for post-recommendation cohorts 1, 2, and 3. In Philadelphia and Milwaukee, loss to follow-up ranged from 8% to 16% in all cohorts.
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The population served by the participating clinics was ethnically and racially diverse. African Americans accounted for 49% of the clientele in Philadelphia, 53% in Jacksonville, and 38% in Milwaukee. Hispanics accounted for 25% of the clientele in Philadelphia, 4% in Jacksonville, and 45% in Milwaukee. The percentage of Caucasian clients ranged from less than 10% in Philadelphia and Milwaukee to approximately 36% in Jacksonville.
Uptake of DTaP and IPV In each of the three cities, clinics administered only DTP to the pre-recommendation cohort and administered DTaP to 89% or more of the infants in all post-recommendation cohorts. OPV was administered to 88% or more of infants in the pre-recommendation cohort, while IPV was given to 83% or more of infants in all post-recommendation cohorts. Differences in the use of DTP and OPV between the pre-recommendation cohort and each of the post-recommendation cohorts were all significant (chi-square test, p⬍0.001).
Simultaneous Injections at the 2- and 4-Month Visits The number of injections administered to infants at the 2- and 4-month immunization visits increased between the pre-recommendation cohort and post-recommendation cohorts in all cities. In all cities, most (ⱖ90%) children received one or two injections at the 2- and 4-month visit in the pre-recommendation cohort, and most (ⱖ78%) infants received three or four injections in all post-recommendation cohorts. In each city and each cohort, the difference between the pre-recommendation cohorts receiving one or two injections and the post-recommendation cohorts receiving three or four injections was significant (p⬍0.05).
UTD Status: 3, 5, 7, and 12 Months Overall immunization coverage rates at age 3 months remained relatively constant in Philadelphia and Milwaukee for the pre-recommendation and the three post-recommendation cohorts. In Jacksonville, immunization coverage rates at age 3 months were lower in the first post-recommendation cohort than in the prerecommendation cohort; rates rose in the second postrecommendation cohort and decreased in the third post-recommendation cohort (Figure 1, A). The UTD status of enrolled infants at ages 5 and 7 months generally followed the same trend as the UTD status at age 3 months in comparing cohorts pre- and post-recommendation of IPV and DTaP (Figure 1, B). Across all cities, the UTD status of infants at age 12 months was slightly higher in the post-recommendation cohorts than in the pre-recommendation cohorts (Figure 1, C).
Discussion We have shown that four injections at an infant’s 2- and 4-month immunization visits are, in practice, acceptable to parents and providers. Prior investigations had reported conflicting results regarding the acceptance of multiple simultaneous injections to parents and providers.25–28 In a study of parent attitudes, the majority of 342 surveyed parents expressed discomfort at the idea of having their child receive three injections at one clinic visit.25 Physicians surveyed by Woodin et al.26 expressed strong concern about infants receiving three and four injections at one visit. On the other hand, studies by Melman et al.27,29 concluded that, despite concerns regarding parental resistance to multiple simultaneous injections, their inner-city clinic population overwhelmingly complied with physicians’ recommendations for multiple injections at vaccination visits. Melman et al.27,29 conducted two studies at an innercity pediatric clinic: the first examining parental attitudes and the second parental behavior associated with their infants receiving multiple simultaneous injections. In the first study,27 parents were presented with hypothetical situations in which their child would receive 2, 3, or 4 injections at one visit. Given a scenario of three needed injections, approximately 40% preferred to divide the injections between two visits. For four injections, nearly 60% preferred two visits. In the second study,29 of children due for two or more immunization injections, over 98% of parents complied with physicians’ recommendations that their child receive two, three, and four injections at one visit, and 88.9% complied with five injections. The acceptance of IPV and DTaP in our study supports the findings of Melman et al.27,29 and demonstrates the feasibility of implementing immunization schedules requiring up to four injections at one visit. Providers rapidly implemented new ACIP recommendations for IPV and DTaP, and parents were receptive to these provider practice changes. This rapid acceptance and uptake of vaccine is particularly important for IPV, due to the need to reduce VAPP cases and the controversy involved in the switch from OPV to IPV. Recent recommendations of new immunizations, such as varicella, were not implemented as rapidly.30 However, the recommendations of IPV and DTaP represent modifications of widely accepted vaccines, rather than a recommendation for a completely new vaccine. The rapid adoption of IPV and DTaP by immunization providers in this study could also be attributed to the willingness of the provider clinics to institute policies recommending the use of IPV and DTaP. Another factor that may have influenced the rapid adoption of these vaccines is that both IPV and DTaP are safer vaccines than their predecessors, OPV and DTP. In all cities and cohorts, at pre- and post-recommendation of IPV and DTaP, immunization coverage levels Am J Prev Med 2001;21(4)
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Figure 1. Overall immunization coverage at 3 months, 5 months, and 12 months for DTP/DTaP (diphtheria, tetanus, and acellular pertussis), polio, Hib (Haemophilus influenza type b), and HepB (hepatitis B)
at age 12 months remained approximately the same. In fact, all post-recommendation cohorts had slightly higher immunization levels at 12 months than children in pre-recommendation cohorts. This finding supports the assertion made in other studies29,31–33 that the recommendation of IPV and DTaP, resulting in up to four injections at the 2- and 4-month immunization visits, is acceptable to parents and providers. In Philadelphia and Milwaukee, immunization cover264
age levels for infants at 3, 5, and 7 months of age were approximately the same in the post-recommendation cohorts as compared to the pre-recommendation cohorts. In Jacksonville, pre- and post-recommendation immunization coverage level comparisons fluctuated at ages 3, 5, and 7 months. Several factors may have influenced coverage levels. Jacksonville experienced a drop in enrollment in their participating public health clinics during the study period following an increase in
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Medicaid managed– care services. Medicaid managed– care services likely led to more infants receiving vaccinations at Medicaid managed– care providers and moving from public clinics to Medicaid managed– care providers. Because the Medicaid eligibility of families frequently changes, children also moved between Medicaid managed– care providers and public health clinics for care, leading to disruption of timely receipt of immunizations. In addition, between the pre-recommendation cohort and the first post-recommendation cohort, the largest clinic participating in the study relocated, coinciding with a delay in many infants in the first post-recommendation cohort receiving their first immunizations. Parents of these infants may have experienced difficulty in locating the new clinic site, as supported by the finding of most of these children catching up with their immunizations by age 12 months. By age 12 months, Jacksonville infants in the postrecommendation cohorts had higher immunization coverage levels than those in the pre-recommendation cohort. This finding reflects that public health clinics in Jacksonville were able to bring infants who used public health clinics as their primary immunization provider UTD by age 12 months. The infants in Jacksonville also tended to be late starters for immunizations, but were able to reach UTD status by age 12 months. Strengths of this study include the collection of data in geographically diverse areas and in publicly funded clinics in areas at high risk for underimmunization. The study included a review of individual immunization records and use of age-defined cohorts that were allowed to grow in size as children within that age group entered participating clinics. Data were validated through follow-up of children not UTD at age 12 months. Follow-up included more than one additional immunization provider if necessary. This study has limitations of method and scope. This study is methodologically limited because it was not designed to be nationally representative. The study is limited in scope because it cannot answer all important questions regarding multiple simultaneous injections, particularly in private provider offices and in managed care settings. In addition, the impact of IPV cannot be isolated from that of DTaP because of the simultaneous adoption of these vaccines. Finally, we cannot assess the immunization coverage levels of children lost to followup. This limitation is particularly important in Jacksonville, where losses to follow-up were the highest. The successful implementation of ACIP’s IPV and DTaP recommendations demonstrates strong support for acceptance and implementation of these vaccines. However, this success does not guarantee that a schedule with different antigens would be as acceptable. Furthermore, the acceptability of more than four injections per visit is unclear. Now that the recommended childhood immunization schedule includes the pneu-
mococcal conjugate vaccine and a fifth injection at the 2-month and 4-month immunization visits, early assessment of vaccine uptake and coverage levels could alert programs and policymakers to overall acceptance or rejection of the new vaccination schedule. We are grateful to Lawrence Barker, Kris Bisgard, and Mehran Massoudi for input into study design; Andrew Chilkatowsky, Lisa Bartlett, and Ann Devonald for their assistance with data collection; and Felicita David for her assistance with data analysis. In Philadelphia, we thank Jim Lutz, Barbara Watson, and Bob Levinson, Philadelphia Department of Public Health; Mark Lyons and Peter Jackson, Maria del Santos and Fairmont Federally Qualified Health Centers; Shoshana Melman, St. ChrisCare Pediatric Services; and Cheryl Hausmann, Albert Einstein Medical Center. In Florida, we thank Henry Janowski, Florida Department of Health; and David Page and Margaret Varnadore, Duval County Health Department. In Wisconsin, we are grateful for the assistance of Dan Hopfensperger and Jacqueline Kowalski, Wisconsin Department of Health and Family Services; John Tranetzki, City of Milwaukee Health Department; John Carroll, 16th Street Community Health Center; Dan Torphy, Downtown Health Center; and John Humphrey, Sinai-Samaritan Pediatric Clinic. Finally, we are sincerely grateful to the staff of all participating clinics for their support of this study. This study was approved by the Institutional Review Board of the Centers for Disease Control and Prevention. Informed consent to contact additional immunization providers was requested of parents of children not up-to-date for immunizations. This study was presented in part at the annual meetings of the Pediatric Academic Society, May 2000, Boston, MA, and the American Public Health Association, November 1999, Chicago, IL.
References 1. Centers for Disease Control and Prevention. Poliomyelitis prevention in the United States. Introduction of a sequential vaccination schedule of inactivated polio virus vaccine followed by oral polio vaccine: recommendation of the Advisory Committee on Immunization Practices. MMWR Morb Mortal Wkly Rep 1997;46(RR-3):1–24. 2. Prevots DR, Strebel PM. Poliomyelitis prevention in the United States: new recommendations for routine childhood immunization place greater reliance on inactivated polio virus vaccine. Pediatric Ann 1997;26:378 –3. 3. Centers for Disease Control and Prevention. Pertussis vaccination. Use of acellular pertussis vaccines among infants and young children: recommendation of the Advisory Committee on Immunization Practices. MMWR Morb Mortal Wkly Rep 1997;46(RR-7):1–25. 4. American Academy of Pediatrics. Active and passive immunization. In: Peter G, ed. 1997 Red Book: report of the Committee on Infectious Diseases, 24th ed. Elk Grove Village, IL: American Academy of Pediatrics, 1997:1–71. 5. Centers for Disease Control and Prevention. Notice to readers: recommended childhood immunization schedule—United States, 1997. MMWR Morb Mortal Wkly Rep 1997;46:35– 40. 6. Centers for Disease Control and Prevention. Revised recommendations for routine poliomyelitis vaccination: recommendations of the Advisory Committee on Immunization Practices. MMWR Morb Mortal Wkly Rep 1999; 48:590. 7. American Academy of Pediatrics. Active and passive immunization. In: Pickering LK, ed. 2000 Red Book: report of the Committee on Infectious Diseases, 25th ed. Elk Grove Village, IL: American Academy of Pediatrics, 2000:22–23. 8. Centers for Disease Control and Prevention. Notice to readers: recom-
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mended childhood immunization schedule—United States, 2000. MMWR Morb Mortal Wkly Rep 2000;49:35– 47. Judelsohn R. The CDC’s proposed revision of polio immunization policy: is it wise? Am J Public Health 1996;86:890. Judelsohn, R. Changing the US polio immunization schedule would be bad public health policy. Pediatrics 1996;98:115– 6. Paradiso PR. The future of polio immunization in the United States: are we ready for a change? Pediatr Infect Dis J 1996;15:645–9. Adler P. Changing polio immunization policy: a big mistake. Infect Dis Clin Pract 1996;5:285– 6. Marwick C. Decision— but no unanimity— on polio vaccine use. JAMA 1996;276:1210. Marwick C. Not everyone wants IPV: opposition gears up. JAMA 1995;270: 1574 –5. Finn A, Bell F. Polio vaccine: is it time for a change? Arch Dis Child 1998;78:571–3. Katz SL. Poliovaccine policy: time for a change. Pediatrics 1996;98:116 –7. Barlett MJ, Burgess MA, McIntyre PB, Heath TC. Parent and general practitioner preference for infant immunization: reactogenicity or multiple injections? Aust Fam Physician 1999;28:22–7. Hutchins SS, Gindler JS, Atkinson WL, et al. Preschool children at high risk for measles: opportunities to vaccinate. Am J Public Health 1993;83:862–7. Wood D, Donald-Sherbourne C, Halfon N, et al. Factors related to immunization status among inner-city Latino and African-American Preschoolers. Pediatrics 1995;96:295–301. National Vaccine Advisory Committee. The measles epidemic: the problems, barriers, and recommendations. JAMA 1991;26:1547–52. Gindler JS, Atkinson WL, Markowitz LE. Update: the United States measles epidemic, 1989 –1990. Epidemiol Rev 1992;14:270 – 6. Zell ER, Dietz V, Stevenson J, Cochi S, Bruce RH. Low vaccination levels of U.S. preschool and school-age children: retrospective assessments of vaccination coverage, 1991–1992. JAMA 1994;271:833–9. Ewert D, Thomas CJ, Chun LY, et al. Measles vaccination coverage among
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Latino children aged 12–59 months: a household survey. Am J Public Health 1991;81:1057–9. National Immunization Program. Clinic Assessment Software Application (CASA), modified version 3. Atlanta, GA: Department of Health and Human Services, 1996. Madlon-Kay DJ, Harper PG. Too many shots? Parent, nurse and physician attitudes toward multiple simultaneous childhood vaccinations. Arch Fam Med 1994;3:610 –7. Woodin KA, Rodewald LE, Humiston SG, Carges MS, Schaffer SJ, Szilagyi PG. Physician and parents opinions: are children becoming pincushions from immunizations? Arch Pediatr Adolesc Med 1995;149:845–9. Melman ST, Chawla T, Kaplan JM, Anbar RD. Multiple injections: Ouch! Arch Fam Med 1994;3:615– 8. Kolasa M, Brink E, Dibling K, Rheaume C, Corwin S. Nursing attitudes regarding the sequential IPVOPV schedule. Paper presented at Annual Meeting of the American Public Health Association, Indianapolis, IN, November 1997. Melman ST, Nguyen TT, Ehrlich ES, Schorr M, Anbar RD. Parental compliance with multiple immunization injections. Arch Pediatr Adolesc Med 1999;153:1289 –91. Watson B, Rothstein E. Varicella vaccine: progress 4 years after licensure. Pediatr Ann 1999;28:516 –29. Kolasa M, Desai S, Bisgard K, Dibling K, Prevots D. Impact of the introduction of the sequential poliovirus vaccination schedule: a demonstration project in one county in Georgia, United States. Am J Prev Med 2000;18:140 –5. Centers for Disease Control and Prevention. Impact of the sequential IPV/OPV schedule on vaccination coverage levels—United States, 1997. MMWR Morb Mortal Wkly Rep 1998;47:1017–9. Dunn RA, Martin D, Schultz A. Choice of polio vaccination schedule and 12-month immunization levels: findings of the Michigan State University prospective cohort study. Paper presented at 32nd National Immunization Conference, Dallas, TX, June 1999.
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Immunization coverage was assessed in public clinics in three urban areas before and after the recommendations. One pre- and three post-recommendation cohorts were followed to 12 months of age.
Results:
Almost all (ⱖ88%) infants in the pre-recommendation cohort received OPV, DTP, and only one or two injections. Almost all (ⱖ78%) infants in the post-recommendation cohorts received IPV, DTaP, and three or four injections. The percentage of infants in the post-recommendation cohorts up-to-date for immunizations at 12 months of age was slightly higher than those in the pre-recommendation cohort.
Conclusions: Providers rapidly switched from OPV and DTP to IPV and DTaP. Coverage at 12 months of age was higher among IPV/DTaP recipients than among OPV/DTP recipients. Provider and parent acceptance of four injections at a visit was high. The recent pneumococcal conjugate vaccine recommendations potentially add a fifth injection at 2 and 4 months of age. Acceptance or rejection of five injections by providers and parents needs early assessment. Medical Subject Headings (MeSH): diphtheria–tetanus–pertussis vaccine; immunization; injections; poliovirus vaccine, inactivated (Am J Prev Med 2001;21(4):261–266)
Background
R
ecommendations for routine vaccination against polio, diphtheria, tetanus, and pertussis changed in early 1997, resulting in two additional injections at infant’s 2- and 4-month immunization visits. The Advisory Committee on Immunization Practices (ACIP) recommended a preferred schedule of two doses of inactivated poliovirus vaccine (IPV) at 2 and 4 months of age, followed by two doses of oral poliovirus vaccine (OPV) at 12 to 18 months and 4 to 6 years (the “sequential” schedule) in order to decrease the risk of vaccine-associated paralytic polio (VAPP).1,2 In addition, the ACIP, the American Academy of PediFrom the Immunization Services Division, National Immunization Program, Centers for Disease Control and Prevention, Atlanta, Georgia Address correspondence and reprint requests to: Maureen S. Kolasa, RN, MPH, Centers for Disease Control and Prevention (CDC), National Immunization Program, Immunization Services Division, 1600 Clifton Rd, MS E-61, Atlanta, GA 30333. E-mail: [email protected].
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atrics (AAP), and the American Academy of Family Physicians (AAFP) all recommended use of diphtheria, tetanus, and acellular pertussis (DTaP) instead of diphtheria, tetanus, and pertussis (DTP) because the acellular pertussis vaccine is less likely to cause adverse events.3–5 Polio vaccination recommendations were further revised in 1999 when the ACIP, along with AAP and AAFP, recommended an all-IPV schedule.6 – 8 Immunizations against Haemophilus influenzae-type b (Hib) and hepatitis B (HepB) are also recommended at 2 and 4 months.8 Policymakers and immunization providers were concerned that multiple simultaneous injections could decrease immunization coverage levels.9 –17 They reasoned that some children would be unlikely to make additional visits for any delayed vaccinations because of providers’ or parents’ reluctance to accept up to four simultaneous injections. A decrease in immunization coverage is of particular concern for children in urban low-income communities because children in these areas are already at increased risk for vaccine-prevent-
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able disease outbreaks as was seen during the measles resurgence in the early 1990s.18 –23 Because of this concern and the conflicting opinions and studies on this issue, the Centers for Disease Control and Prevention evaluated the introduction of the sequential poliovirus vaccination schedule and DTaP. The goal of the study was to determine the impact of the sequential schedule of IPV/OPV and the licensing of DTaP for infants on childhood immunization coverage. Specific study objectives were to compare overall and vaccine-specific childhood immunization rates for polio, diphtheria, tetanus, pertussis, Hib, and HepB before and after implementation of the sequential schedule of IPV/OPV, and the licensing of DTaP for children ⬍12 months. The study also examined the time to acceptance of IPV and DTaP and the change in the number of injections given per immunization visit.
Methods This study was set in three geographically diverse cities (Philadelphia, Pennsylvania; Jacksonville, Florida; Milwaukee, Wisconsin) in publicly funded health clinics located in areas at risk for underimmunization. The clinics included public health clinics, federally qualified health centers, and university clinics receiving public funds for infant immunization. The clinics served primarily low-socioeconomic-status clients. The management of all participating clinics adopted policies encouraging, but not requiring, healthcare providers to recommend IPV and DTaP to clinic clients. Using the Clinic Assessment Software Application (CASA),24 immunization coverage levels were assessed before and after each clinic’s adoption of the sequential IPV/OPV schedule and use of DTaP in infants. Age-appropriate immunization coverage was determined in the single pre-recommendation birth cohort and in the three post-recommendation birth cohorts in each clinic and city. Because this is a birth cohort design, the study population was enrolled during “enrollment windows” of sufficient duration to achieve the desired sample size. The target sample size for each cohort in each city was 378, the minimum number that would enable detection of a difference in vaccine coverage between the pre- and post-recommendation cohorts of 10 percentage points with power of 0.8 and ␣ of 0.05. Infants in the pre-recommendation cohort were born March through June 1996 and began their immunizations before the recommendation for use of IPV and DTaP in infants. In post-recommendation cohorts, infants were born as follows: Cohort 1, September–December 1997; Cohort 2, January–May 1998; and Cohort 3, June–August 1998. Infants in the first post-recommendation cohorts were eligible for their first immunizations after participating clinics had adopted a policy for use of the sequential IPV/OPV schedule and DTaP. Infants were eligible for inclusion regardless of whether they entered the participating clinic for their first immunizations or transferred into the clinic at an older age. Immunizations administered in nonparticipating clinics were included in the vaccination history of cohort children and
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were coded as having been administered elsewhere. Race/ ethnicity was recorded if available in the patient chart. Infants were excluded from the study cohorts if they did not receive their first dose of DTP/DTaP, Hib, or polio immunization by age 6 months (180 days) or if they did not receive any routine immunizations (DTP/DTaP, Hib, or polio) by age 12 months in the participating clinic. Infants were also excluded if they had no immunization record or if the immunization record was not clear as to which immunizations were received. For example, if the record was not clear if an infant received IPV or OPV, that infant was excluded. If the record was not clear if an infant received DTP, the DTP–Hib combination vaccine, or DTaP, the infant was also excluded. The primary outcome measures were vaccination status at ages 3, 5, 7, and 12 months. This design included a 30-day grace period after the recommended ages for vaccination of 2, 4, and 6 months. Infants were considered age appropriately up-to-date (UTD) for individual vaccines—DTP/DTaP, Hib, HepB, polio vaccine (IPV or OPV)—if they had received one dose by age 3 months and two doses by age 5 months. At age 7 and 12 months, UTD infants had received three doses of DTP/DTaP along with at least two doses of polio, Hib, and HepB immunizations. Enrolled infants could have one of three dispositions from the cohort at age 12 months: (1) complete immunization series, (2) incomplete immunization series, or (3) lost to follow-up. When the enrolled infants reached age 1 year, attempts were made to contact the parents or guardians of those infants whose record indicated that they were not UTD for their immunizations. Five attempts were made to reach parents by telephone. If unsuccessful, an attempt was made to contact the parents via mail. If reached, parents were requested to provide the names of additional immunization providers for their infant and consent for contact of these providers. Additional immunization providers were then contacted for the infant’s immunization history. Infants UTD for immunizations at age 12 months according to participating clinic information were included in the final analysis. We also included infants not UTD according to participating clinic records, but whose parents were successfully contacted to determine if their infants received immunizations elsewhere. Infants whose immunization records indicated that they were not UTD at age 12 months and whose parents could not be located or who refused to provide information were considered lost to follow-up.
Results Initial enrollment for each cohort ranged from 383 to 489 in Philadelphia, 383 to 524 in Jacksonville, and 371 to 400 in Milwaukee. Final enrollment, after excluding those lost to follow-up, ranged from 350 to 448 in Philadelphia, 285 to 467 in Jacksonville, and 332 to 351 in Milwaukee. The greatest loss occurred in Jacksonville, with 11% lost to follow-up in the pre-recommendation cohort, and 19%, 24%, and 31%, respectively, for post-recommendation cohorts 1, 2, and 3. In Philadelphia and Milwaukee, loss to follow-up ranged from 8% to 16% in all cohorts.
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The population served by the participating clinics was ethnically and racially diverse. African Americans accounted for 49% of the clientele in Philadelphia, 53% in Jacksonville, and 38% in Milwaukee. Hispanics accounted for 25% of the clientele in Philadelphia, 4% in Jacksonville, and 45% in Milwaukee. The percentage of Caucasian clients ranged from less than 10% in Philadelphia and Milwaukee to approximately 36% in Jacksonville.
Uptake of DTaP and IPV In each of the three cities, clinics administered only DTP to the pre-recommendation cohort and administered DTaP to 89% or more of the infants in all post-recommendation cohorts. OPV was administered to 88% or more of infants in the pre-recommendation cohort, while IPV was given to 83% or more of infants in all post-recommendation cohorts. Differences in the use of DTP and OPV between the pre-recommendation cohort and each of the post-recommendation cohorts were all significant (chi-square test, p⬍0.001).
Simultaneous Injections at the 2- and 4-Month Visits The number of injections administered to infants at the 2- and 4-month immunization visits increased between the pre-recommendation cohort and post-recommendation cohorts in all cities. In all cities, most (ⱖ90%) children received one or two injections at the 2- and 4-month visit in the pre-recommendation cohort, and most (ⱖ78%) infants received three or four injections in all post-recommendation cohorts. In each city and each cohort, the difference between the pre-recommendation cohorts receiving one or two injections and the post-recommendation cohorts receiving three or four injections was significant (p⬍0.05).
UTD Status: 3, 5, 7, and 12 Months Overall immunization coverage rates at age 3 months remained relatively constant in Philadelphia and Milwaukee for the pre-recommendation and the three post-recommendation cohorts. In Jacksonville, immunization coverage rates at age 3 months were lower in the first post-recommendation cohort than in the prerecommendation cohort; rates rose in the second postrecommendation cohort and decreased in the third post-recommendation cohort (Figure 1, A). The UTD status of enrolled infants at ages 5 and 7 months generally followed the same trend as the UTD status at age 3 months in comparing cohorts pre- and post-recommendation of IPV and DTaP (Figure 1, B). Across all cities, the UTD status of infants at age 12 months was slightly higher in the post-recommendation cohorts than in the pre-recommendation cohorts (Figure 1, C).
Discussion We have shown that four injections at an infant’s 2- and 4-month immunization visits are, in practice, acceptable to parents and providers. Prior investigations had reported conflicting results regarding the acceptance of multiple simultaneous injections to parents and providers.25–28 In a study of parent attitudes, the majority of 342 surveyed parents expressed discomfort at the idea of having their child receive three injections at one clinic visit.25 Physicians surveyed by Woodin et al.26 expressed strong concern about infants receiving three and four injections at one visit. On the other hand, studies by Melman et al.27,29 concluded that, despite concerns regarding parental resistance to multiple simultaneous injections, their inner-city clinic population overwhelmingly complied with physicians’ recommendations for multiple injections at vaccination visits. Melman et al.27,29 conducted two studies at an innercity pediatric clinic: the first examining parental attitudes and the second parental behavior associated with their infants receiving multiple simultaneous injections. In the first study,27 parents were presented with hypothetical situations in which their child would receive 2, 3, or 4 injections at one visit. Given a scenario of three needed injections, approximately 40% preferred to divide the injections between two visits. For four injections, nearly 60% preferred two visits. In the second study,29 of children due for two or more immunization injections, over 98% of parents complied with physicians’ recommendations that their child receive two, three, and four injections at one visit, and 88.9% complied with five injections. The acceptance of IPV and DTaP in our study supports the findings of Melman et al.27,29 and demonstrates the feasibility of implementing immunization schedules requiring up to four injections at one visit. Providers rapidly implemented new ACIP recommendations for IPV and DTaP, and parents were receptive to these provider practice changes. This rapid acceptance and uptake of vaccine is particularly important for IPV, due to the need to reduce VAPP cases and the controversy involved in the switch from OPV to IPV. Recent recommendations of new immunizations, such as varicella, were not implemented as rapidly.30 However, the recommendations of IPV and DTaP represent modifications of widely accepted vaccines, rather than a recommendation for a completely new vaccine. The rapid adoption of IPV and DTaP by immunization providers in this study could also be attributed to the willingness of the provider clinics to institute policies recommending the use of IPV and DTaP. Another factor that may have influenced the rapid adoption of these vaccines is that both IPV and DTaP are safer vaccines than their predecessors, OPV and DTP. In all cities and cohorts, at pre- and post-recommendation of IPV and DTaP, immunization coverage levels Am J Prev Med 2001;21(4)
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Figure 1. Overall immunization coverage at 3 months, 5 months, and 12 months for DTP/DTaP (diphtheria, tetanus, and acellular pertussis), polio, Hib (Haemophilus influenza type b), and HepB (hepatitis B)
at age 12 months remained approximately the same. In fact, all post-recommendation cohorts had slightly higher immunization levels at 12 months than children in pre-recommendation cohorts. This finding supports the assertion made in other studies29,31–33 that the recommendation of IPV and DTaP, resulting in up to four injections at the 2- and 4-month immunization visits, is acceptable to parents and providers. In Philadelphia and Milwaukee, immunization cover264
age levels for infants at 3, 5, and 7 months of age were approximately the same in the post-recommendation cohorts as compared to the pre-recommendation cohorts. In Jacksonville, pre- and post-recommendation immunization coverage level comparisons fluctuated at ages 3, 5, and 7 months. Several factors may have influenced coverage levels. Jacksonville experienced a drop in enrollment in their participating public health clinics during the study period following an increase in
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Medicaid managed– care services. Medicaid managed– care services likely led to more infants receiving vaccinations at Medicaid managed– care providers and moving from public clinics to Medicaid managed– care providers. Because the Medicaid eligibility of families frequently changes, children also moved between Medicaid managed– care providers and public health clinics for care, leading to disruption of timely receipt of immunizations. In addition, between the pre-recommendation cohort and the first post-recommendation cohort, the largest clinic participating in the study relocated, coinciding with a delay in many infants in the first post-recommendation cohort receiving their first immunizations. Parents of these infants may have experienced difficulty in locating the new clinic site, as supported by the finding of most of these children catching up with their immunizations by age 12 months. By age 12 months, Jacksonville infants in the postrecommendation cohorts had higher immunization coverage levels than those in the pre-recommendation cohort. This finding reflects that public health clinics in Jacksonville were able to bring infants who used public health clinics as their primary immunization provider UTD by age 12 months. The infants in Jacksonville also tended to be late starters for immunizations, but were able to reach UTD status by age 12 months. Strengths of this study include the collection of data in geographically diverse areas and in publicly funded clinics in areas at high risk for underimmunization. The study included a review of individual immunization records and use of age-defined cohorts that were allowed to grow in size as children within that age group entered participating clinics. Data were validated through follow-up of children not UTD at age 12 months. Follow-up included more than one additional immunization provider if necessary. This study has limitations of method and scope. This study is methodologically limited because it was not designed to be nationally representative. The study is limited in scope because it cannot answer all important questions regarding multiple simultaneous injections, particularly in private provider offices and in managed care settings. In addition, the impact of IPV cannot be isolated from that of DTaP because of the simultaneous adoption of these vaccines. Finally, we cannot assess the immunization coverage levels of children lost to followup. This limitation is particularly important in Jacksonville, where losses to follow-up were the highest. The successful implementation of ACIP’s IPV and DTaP recommendations demonstrates strong support for acceptance and implementation of these vaccines. However, this success does not guarantee that a schedule with different antigens would be as acceptable. Furthermore, the acceptability of more than four injections per visit is unclear. Now that the recommended childhood immunization schedule includes the pneu-
mococcal conjugate vaccine and a fifth injection at the 2-month and 4-month immunization visits, early assessment of vaccine uptake and coverage levels could alert programs and policymakers to overall acceptance or rejection of the new vaccination schedule. We are grateful to Lawrence Barker, Kris Bisgard, and Mehran Massoudi for input into study design; Andrew Chilkatowsky, Lisa Bartlett, and Ann Devonald for their assistance with data collection; and Felicita David for her assistance with data analysis. In Philadelphia, we thank Jim Lutz, Barbara Watson, and Bob Levinson, Philadelphia Department of Public Health; Mark Lyons and Peter Jackson, Maria del Santos and Fairmont Federally Qualified Health Centers; Shoshana Melman, St. ChrisCare Pediatric Services; and Cheryl Hausmann, Albert Einstein Medical Center. In Florida, we thank Henry Janowski, Florida Department of Health; and David Page and Margaret Varnadore, Duval County Health Department. In Wisconsin, we are grateful for the assistance of Dan Hopfensperger and Jacqueline Kowalski, Wisconsin Department of Health and Family Services; John Tranetzki, City of Milwaukee Health Department; John Carroll, 16th Street Community Health Center; Dan Torphy, Downtown Health Center; and John Humphrey, Sinai-Samaritan Pediatric Clinic. Finally, we are sincerely grateful to the staff of all participating clinics for their support of this study. This study was approved by the Institutional Review Board of the Centers for Disease Control and Prevention. Informed consent to contact additional immunization providers was requested of parents of children not up-to-date for immunizations. This study was presented in part at the annual meetings of the Pediatric Academic Society, May 2000, Boston, MA, and the American Public Health Association, November 1999, Chicago, IL.
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