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Hepatitis B vaccine in pregnancy: Immunogenicity, safety and transfer of antibodies to infants
Int.J. Gynaecol. Obsstet., 1987, 25: 297-301 International
Federation of Gynaecology & Obstetrics
HEPATITIS B VACCINE lN PREGNANCY: IMMUNOGENICITY, SAFETY AND TRANSFER OF ANTIBODIES TO INFANTS
E.A. AYOOLA and A.O.K. JOHNSON Liver Unit, Department
of Medicine and Paediahcs,
University College Hospital, Ibadan (Nigeria)
(Received February 28th, 1985) (Accepted November 6th, 1986)
Abstract To determine the safety and immunogenicity of hepatitis B vaccine in pregnancy, 72 pregnant Nigerians who were negative for markers of hepatitis B virus (HBV) were given two intramuscular doses of vaccine (Heptavax, n/lerck) in the third trimester. One month after the second dose (at T2), 84% were anti HBs positive. No significant effect was observed in the mothers or their newborns. Passive transfer of anti HBs occurred in S9% of the newborns. The antibodies disappeared rapidly in these infants and by 3 months only 23% had detectable antibodies. No HBsAg carrier status developed in this group. In contrast, the infants born to HbsAg positive mothers had a cummulative rate of HBV events of 20%. It is concluded that HBV vaccine is safe and immunogenic in pregnant females. The passive immunity conferred on the infants is of short duration. Therefore, infants in endemic areas should be vaccinated early, preferably within 3 months of birth. Vaccination of pregnan t mothers may provide adequate protection before the child is vaccinated
Keywords: Hepatitis B vaccine; Immunogenicity; Passive immunisation; Pregnancy. Introduction In contrast to the situation in the Western world, .hepatitis B virus (HBV) infection is 0020-7292/87/$03.50 01987 International Federation of Gynaecology & Obstetrics Published and Printed in Ireland
endemic in Southeast Asia and tropical Africa where the majority of adult populations have evidence of past or present infection. In such areas, chronic hepatitis B surface antigen (HBsAg) carriers may represent lo-20% of the population. These chronic carriers are more predisposed to the development of chronic liver diseases including primary liver cell carcinoma (PLC) [3,91 . Recent data have suggested that most of the HBV infections are acquired very early in life [ 4,8 J . It is now established that active immunization may be the most effective method available for protection against HBV infection. Several studies have documented the efficacy and safety of hepatitis B vaccine in adults and children [ 1,6,7] . During the early part of clinical trials of hepatitis B vaccine, it was discovered that parents were reluctant to allow multiple injections and venepunctures for their healthy infants. This was a frequent reason for noncompliance with clinic appointments. It was therefore considered that immunized pregnant mothers may passively transfer protective levels of antibodies to their respective newborns. Such protection may persist until the child is considered old enough for vaccination. A prospective study was undertaken to determine the safety and efficacy of hepatitis B vaccine in the pregnant female and to determine whether protective levels of antibody to HBsAg (anti-HBs) may be transferred to the infants. Int J Gynaecol Obstet 25
298
Ayoola and Johnson
Materials and methods
The participants in this study were selected from antenatal patients who were attending private and government maternity centers within Ibadan. They were included only if they were literate so that they could read available information on the vaccines. Other requirements included being in their third trimester and having no history of hepatobiliary diseases. Those participants with no HBV markers in their blood were selected for hepatitis B vaccination (Group I). Group II comprised thoSe women with positive anti-HBs only. Participants with positive HBsAg with or without antibody to hepatitis B core antigen (anti-HBc) were included as Group III. Patients with a history of stillbirths or previous complicated labors were excluded from the study. Informed consent was obtained from all the participants. The study was approved by the local ethical committee on medical research. Group I comprised 72 women (aged 1927 years) who were given two 20 E.cgdoses (i.e. 0.5 ml) of hepatitis B vaccine (Heptavax from Merck Sharp and Dohme West Point Pa-lot 82324). The vaccine, containing 40 c(g per ml of HBsAg subtype ad, was given intramuscularly 1 month apart (at To and T,). Groups II and III received vitamin B complex injection as placebo by the same schedule as in Group I. At each monthly visit, blood samples were taken for the detection of HBV markers (HBsAg, anti-HBc and anti-HBs) and for the estimation of serum alanine aminotransferase (ALT). At delivery, a sample of cord blood was obtained; care was taken to avoid contamination with maternal blood. Thereafter, blood samples were obtained from the infants and their mothers monthly for 3 months and at 6 and 12 months. All mothers and infants were examined carefully at each visit and any effects or abnormalities were documented. Sera were stored at -20°C until reagents were available for testing. HBV markers were Int J Gynaecol Obstet 25
detected by radioimmunoassay (RIA) for HBsAg, anti HBs and anti HBc using commercial kits (AUSRIA, II, AUSAB and CORAB) from Abbott Laboratories in Chicago, Illinois, USA. Positive antibody response was an increase of anti-HBs (AUSAB Ru) from less to greater than 2.1 without concomittant presence of anti HBc or HBsAg. Anti HBs titre was estimated as recommended by the manufacturers and may be converted to milli international units (mIU) by standard curves [ 51. Serum ALT was estimated enzymatically by standard methods. Statistical analysis was performed using the chi square and the t-test. Recipients who seroconverted from antiHBs negative to positive in the absence of any serologic markers suggestive of HBV replication (HBsAg or anti-HBc) were said to have a vaccine response. These were referred to as responders. Those without anti-HBs were non-responders. Hepatitis B virus events were separated into three categories: (a) those with acute hepatitis, comprising recipients who had seroconversion from negative to positive for HBsAg or antiHBc or both with elevation of ALT (at least twice the normal level) on two occasions 1 week apart; (b) those with HBsAg antigenemia without hepatitis, consisted of recipients who seroconverted from HBsAg negative to positive while normal ALT levels are maintained; (c) those who seroconverted from negative to positive anti-HBc without detectable HBsAg or elevated ALT levels. Results Safety
None of the participants developed any serious effect to the vaccine. Table I summarises the complaints in all groups. The fever in the 4 cases responded to antimalaria treatment. There were 2 cases of stillbirth in the three groups. One case (Group I) was due to an obstructed labor due to an abnormal lie, and the other case (Group III) was due to an intrauterine death of unknown cause. The two pairs were excluded from further analysis.
Hepatitis B vaccine in pregnancy
Table 1.
Effects in vaccinated and control
rates (Table III) and in titres after the second month of birth (Table IV).
groups.
Complaints
Group I (n = 72)
Group II (n = 65)
Group III (n = 21)
Pain at injection sites Fatigue Headache Fever Others (e.g. pruritus dizziness, increased appetite)
9 2 2 2 3
7 3 1 1 4
4 1 1 1 1
HB V events in infants
None of the infants in Groups I and II developed acute hepatitis B during the followup period irrespective of the response to vaccination. In contrast, 2 of the 21 infants in Group III were diagnosed as having possible anicteric hepatitis between the ages of 6 and 12 months. None of these two had persistent HBsAg. Table V summarises the HBV events in all three groups.
Maternal response
The immunogenic response in 72 vaccinated pregnant mothers (Group I) was compared to the immune status of previous immunised (by natural infection) mothers in Table II. The mean titres in the latter group was significantly higher than in Group I (P < 0.00 1).
Loss to follow up
Compliance was complete until after 6 months when 12 infants were not evaluated in the entire group. Two cases of infant mortality were recorded from measles and pneumonia (Group II), and in 1 case due to cows urine concoction poisoning (Group III). Four parents (Group II), and in 1 case due to cows urine concoction poisoning (Group II). Four parents (3 in Group I and 1 in Group II) had moved. There was no information in 2 cases (Group I).
Transfer of antibodies
Of the 6 1 neonates born to vaccine responders, 59% had detectable anti-HBs at birth. Comparatively, 66% of neonates in group II had transferred maternal antibodies. The antiHBs in these infants decreased rapidly both in
Table II.
Immunogenic response to vaccination in pregnant women,
Groups
No.
Vaccinated Previously immunized
Table III. Maternal groups
Group I Group II
299
72 65
No. (%) with positve anti-HBs at
Titres (mIU) at T,
TP
T,
T,
T,
Range
Mean
0 (0) 65(100)
24( 33.3) 65(100)
61(84.7) 64(98.5)
60(83.3) 63(96.9)
3.5-912 8-1600
121.4 232.6
Passive transfer of anti-HBs from mother to child. No. of infants born to antiRBs positive mothers
No. (%) of infants with passively transferred anti HBs at: Birth
1
2
3
6 (months)
61 65
36(59) 43(66.2)
28(45.9) 38(58.5)
18(29.5) 28(43.1)
14(23) 23(35.4)
3(4.9) 8G2.3)
Int J Gynaecol Obstet 25
300
Ayookr and Johnson
Table IV. Anti-HBs titres (mIU) in infants born to anti-HBs positive mothers. Titres of anti-HBs(mIU) of age
in the tlrst 6 months
1
2
3
6
Group I Mean (range) n
35 (3.5-84) 28
16.5 (3-63) 20
9.6 (4-20) 16
(E-5) 3
Group II Mean (range) n
64.5 (4-124) 28
38.2 (35-80) 28
21.5 (2.5-36) 23
(!“32) 8
Discussion The study indicated the safety of hepatitis vaccine in the third trimester of pregnancy, In some tropical areas, including Nigeria, anti-tetanus immunization is recommended in selected communities during the third trimester with the expectation of extending the induced immunity to the newborn. This concept can be evaluated with regard to hepatitis B infection. The high immunogenicity of the available vaccines was confirmed in the present group in which 84% became anti HBs positive after vaccination. The safety of the fetus also was demonstrated, and no abnormal birth defect was observed. The stillbirths recorded occurred both in the vaccinated group and in the
Table V. Maternal groups
I
II III
controls from obstetric complications. As expected, passive transfer of ‘antibodies did occur following vaccination. However, the titres in this group were generally lower than in infants born to previously immunized mothers (Group II). This probably derives from the relatively higher titres of circulating antibodies in the latter group. Irrespective of the maternal group, anti HBs was rapidly cleared from the circulation of the infants. Protective levels of anti HBs were uncommonly detected after 2 months of age, and by 6 months the majority of the infants had little or no protection from maternal antibodies. It is therefore suggested that infants in endemic areas be vaccinated within 6 months of birth, and preferably before the age of 3 months. It was interesting to observe the relatively high incidence of HBV event in infants born to HBsAg positive mothers. This pattern was not only the consequence of vertical (motherchild) transmission [ 21 but also of horizontal (contact) transmission. This category of infants should therefore be considered for hepatitis vaccination much earlier than 3 months. Acknowledgment We thank Merck, Sharp and Dohme for providing some of the vaccines. We acknowledge the invaluable help of the midwives in the maternity centres and private hospitals. Mr. Debo Omoyele kindly provided the secretarial support.
HBsAg in infants born to the different groups. HBV markers (maternal status)
(a) Anti-HBs positive (vaccinated) (b) Anti-HBs negative (vaccinated) Anti-HBs positive (placebo) HBs positive (placebo)
Znt J Gynaecol Obstet 25
No. of infants
No. positive for HBsAg at Birth
1
3
6
12 (months)
61
0
0
0
1
2 (n = 54)
11
0
0
0
0
1 (n = 11)
65 21
0 9
0 5
0 3
1 3
1 (n = 61) 3 (n = 20)
Hepatitis B vaccine in pregnancy
References 1 Ayoola EA: The immune response of healthy Nigerian adults to small dose of hepatitis B vaccine. Comparison of 10 and 20 fig doses. J Med Vlrol13: 223,1984. 2 Ayoola EA, Ogunbode 0, Odelola HA: Congenital transmission of hepatitis B antigen in Nigerians. Arch Virol 67: 97, 1981. 3 Beasley RP, Hwang LY, Lin CC, Chien CB: Hepatocellular carcinoma and hepatitis B virus. A prospective study of 22707 men in Taiwan. Lancet ii: 1129,198l. 4 Blumberg BS, London WT: Hepatitis B virus and primary hepatocellular carcinoma: relationship of ICRONS to cancer. In: Viruses in Naturally Occurring Cancer (eds M Essex, G Tedero, H Zur Hausen), Cold Spring Harbor Conference on cell proliferation, Vol 7, pp 401-421 Cold Spring Harbor Laboratory, New York, 1980. 5 Hollinger FB, A&m I, Heiberg D, Melnick JL: Response to hepatitis B vaccine in a young adult population. In Viral Hepatitis (eds W Szmuness, HJ Alter, JE Maynard), pp 451-466. 6 Maupas P, Chiron JP, Goudeau A, Coursaget P, Perrin J, Barin F, Denis F, Diop-Mar I: Active immunization
301
against hepatitis B in an area of high endemicity. Part II: Prevention of early infection of the child. Prog Med Virol27: 188,198l. Szmuness W, Stevens CE, Harley EJ, Znak EA, Oleszko WR, William DC, Sadousky R, Morrison JM, Kellner A: Hepatitis B vaccine: demonstration of efficacy in a controlled clinical trial in a high risk population in the United States. N Engl. J Med 202: 883, 1980. Tong MJ, Thursby MW, Lin JH, Weissmann JY, Mcpeak CM: Studies on the maternal-infant transmission of the hepatitis B virus and HBV infection within families. Prog MedVirol27: 137,198l. William AO: Hepatitis B surface antigen and Liver cell carcinoma. Am J Med Sci270: 53,197s.
Address for reprints: Prof. E.A. Ayoola P.O. Box 7629 Secretariat P.O. Ibadan Nigeria
ZntJ Gynaecol Obstet 25
Federation of Gynaecology & Obstetrics
HEPATITIS B VACCINE lN PREGNANCY: IMMUNOGENICITY, SAFETY AND TRANSFER OF ANTIBODIES TO INFANTS
E.A. AYOOLA and A.O.K. JOHNSON Liver Unit, Department
of Medicine and Paediahcs,
University College Hospital, Ibadan (Nigeria)
(Received February 28th, 1985) (Accepted November 6th, 1986)
Abstract To determine the safety and immunogenicity of hepatitis B vaccine in pregnancy, 72 pregnant Nigerians who were negative for markers of hepatitis B virus (HBV) were given two intramuscular doses of vaccine (Heptavax, n/lerck) in the third trimester. One month after the second dose (at T2), 84% were anti HBs positive. No significant effect was observed in the mothers or their newborns. Passive transfer of anti HBs occurred in S9% of the newborns. The antibodies disappeared rapidly in these infants and by 3 months only 23% had detectable antibodies. No HBsAg carrier status developed in this group. In contrast, the infants born to HbsAg positive mothers had a cummulative rate of HBV events of 20%. It is concluded that HBV vaccine is safe and immunogenic in pregnant females. The passive immunity conferred on the infants is of short duration. Therefore, infants in endemic areas should be vaccinated early, preferably within 3 months of birth. Vaccination of pregnan t mothers may provide adequate protection before the child is vaccinated
Keywords: Hepatitis B vaccine; Immunogenicity; Passive immunisation; Pregnancy. Introduction In contrast to the situation in the Western world, .hepatitis B virus (HBV) infection is 0020-7292/87/$03.50 01987 International Federation of Gynaecology & Obstetrics Published and Printed in Ireland
endemic in Southeast Asia and tropical Africa where the majority of adult populations have evidence of past or present infection. In such areas, chronic hepatitis B surface antigen (HBsAg) carriers may represent lo-20% of the population. These chronic carriers are more predisposed to the development of chronic liver diseases including primary liver cell carcinoma (PLC) [3,91 . Recent data have suggested that most of the HBV infections are acquired very early in life [ 4,8 J . It is now established that active immunization may be the most effective method available for protection against HBV infection. Several studies have documented the efficacy and safety of hepatitis B vaccine in adults and children [ 1,6,7] . During the early part of clinical trials of hepatitis B vaccine, it was discovered that parents were reluctant to allow multiple injections and venepunctures for their healthy infants. This was a frequent reason for noncompliance with clinic appointments. It was therefore considered that immunized pregnant mothers may passively transfer protective levels of antibodies to their respective newborns. Such protection may persist until the child is considered old enough for vaccination. A prospective study was undertaken to determine the safety and efficacy of hepatitis B vaccine in the pregnant female and to determine whether protective levels of antibody to HBsAg (anti-HBs) may be transferred to the infants. Int J Gynaecol Obstet 25
298
Ayoola and Johnson
Materials and methods
The participants in this study were selected from antenatal patients who were attending private and government maternity centers within Ibadan. They were included only if they were literate so that they could read available information on the vaccines. Other requirements included being in their third trimester and having no history of hepatobiliary diseases. Those participants with no HBV markers in their blood were selected for hepatitis B vaccination (Group I). Group II comprised thoSe women with positive anti-HBs only. Participants with positive HBsAg with or without antibody to hepatitis B core antigen (anti-HBc) were included as Group III. Patients with a history of stillbirths or previous complicated labors were excluded from the study. Informed consent was obtained from all the participants. The study was approved by the local ethical committee on medical research. Group I comprised 72 women (aged 1927 years) who were given two 20 E.cgdoses (i.e. 0.5 ml) of hepatitis B vaccine (Heptavax from Merck Sharp and Dohme West Point Pa-lot 82324). The vaccine, containing 40 c(g per ml of HBsAg subtype ad, was given intramuscularly 1 month apart (at To and T,). Groups II and III received vitamin B complex injection as placebo by the same schedule as in Group I. At each monthly visit, blood samples were taken for the detection of HBV markers (HBsAg, anti-HBc and anti-HBs) and for the estimation of serum alanine aminotransferase (ALT). At delivery, a sample of cord blood was obtained; care was taken to avoid contamination with maternal blood. Thereafter, blood samples were obtained from the infants and their mothers monthly for 3 months and at 6 and 12 months. All mothers and infants were examined carefully at each visit and any effects or abnormalities were documented. Sera were stored at -20°C until reagents were available for testing. HBV markers were Int J Gynaecol Obstet 25
detected by radioimmunoassay (RIA) for HBsAg, anti HBs and anti HBc using commercial kits (AUSRIA, II, AUSAB and CORAB) from Abbott Laboratories in Chicago, Illinois, USA. Positive antibody response was an increase of anti-HBs (AUSAB Ru) from less to greater than 2.1 without concomittant presence of anti HBc or HBsAg. Anti HBs titre was estimated as recommended by the manufacturers and may be converted to milli international units (mIU) by standard curves [ 51. Serum ALT was estimated enzymatically by standard methods. Statistical analysis was performed using the chi square and the t-test. Recipients who seroconverted from antiHBs negative to positive in the absence of any serologic markers suggestive of HBV replication (HBsAg or anti-HBc) were said to have a vaccine response. These were referred to as responders. Those without anti-HBs were non-responders. Hepatitis B virus events were separated into three categories: (a) those with acute hepatitis, comprising recipients who had seroconversion from negative to positive for HBsAg or antiHBc or both with elevation of ALT (at least twice the normal level) on two occasions 1 week apart; (b) those with HBsAg antigenemia without hepatitis, consisted of recipients who seroconverted from HBsAg negative to positive while normal ALT levels are maintained; (c) those who seroconverted from negative to positive anti-HBc without detectable HBsAg or elevated ALT levels. Results Safety
None of the participants developed any serious effect to the vaccine. Table I summarises the complaints in all groups. The fever in the 4 cases responded to antimalaria treatment. There were 2 cases of stillbirth in the three groups. One case (Group I) was due to an obstructed labor due to an abnormal lie, and the other case (Group III) was due to an intrauterine death of unknown cause. The two pairs were excluded from further analysis.
Hepatitis B vaccine in pregnancy
Table 1.
Effects in vaccinated and control
rates (Table III) and in titres after the second month of birth (Table IV).
groups.
Complaints
Group I (n = 72)
Group II (n = 65)
Group III (n = 21)
Pain at injection sites Fatigue Headache Fever Others (e.g. pruritus dizziness, increased appetite)
9 2 2 2 3
7 3 1 1 4
4 1 1 1 1
HB V events in infants
None of the infants in Groups I and II developed acute hepatitis B during the followup period irrespective of the response to vaccination. In contrast, 2 of the 21 infants in Group III were diagnosed as having possible anicteric hepatitis between the ages of 6 and 12 months. None of these two had persistent HBsAg. Table V summarises the HBV events in all three groups.
Maternal response
The immunogenic response in 72 vaccinated pregnant mothers (Group I) was compared to the immune status of previous immunised (by natural infection) mothers in Table II. The mean titres in the latter group was significantly higher than in Group I (P < 0.00 1).
Loss to follow up
Compliance was complete until after 6 months when 12 infants were not evaluated in the entire group. Two cases of infant mortality were recorded from measles and pneumonia (Group II), and in 1 case due to cows urine concoction poisoning (Group III). Four parents (Group II), and in 1 case due to cows urine concoction poisoning (Group II). Four parents (3 in Group I and 1 in Group II) had moved. There was no information in 2 cases (Group I).
Transfer of antibodies
Of the 6 1 neonates born to vaccine responders, 59% had detectable anti-HBs at birth. Comparatively, 66% of neonates in group II had transferred maternal antibodies. The antiHBs in these infants decreased rapidly both in
Table II.
Immunogenic response to vaccination in pregnant women,
Groups
No.
Vaccinated Previously immunized
Table III. Maternal groups
Group I Group II
299
72 65
No. (%) with positve anti-HBs at
Titres (mIU) at T,
TP
T,
T,
T,
Range
Mean
0 (0) 65(100)
24( 33.3) 65(100)
61(84.7) 64(98.5)
60(83.3) 63(96.9)
3.5-912 8-1600
121.4 232.6
Passive transfer of anti-HBs from mother to child. No. of infants born to antiRBs positive mothers
No. (%) of infants with passively transferred anti HBs at: Birth
1
2
3
6 (months)
61 65
36(59) 43(66.2)
28(45.9) 38(58.5)
18(29.5) 28(43.1)
14(23) 23(35.4)
3(4.9) 8G2.3)
Int J Gynaecol Obstet 25
300
Ayookr and Johnson
Table IV. Anti-HBs titres (mIU) in infants born to anti-HBs positive mothers. Titres of anti-HBs(mIU) of age
in the tlrst 6 months
1
2
3
6
Group I Mean (range) n
35 (3.5-84) 28
16.5 (3-63) 20
9.6 (4-20) 16
(E-5) 3
Group II Mean (range) n
64.5 (4-124) 28
38.2 (35-80) 28
21.5 (2.5-36) 23
(!“32) 8
Discussion The study indicated the safety of hepatitis vaccine in the third trimester of pregnancy, In some tropical areas, including Nigeria, anti-tetanus immunization is recommended in selected communities during the third trimester with the expectation of extending the induced immunity to the newborn. This concept can be evaluated with regard to hepatitis B infection. The high immunogenicity of the available vaccines was confirmed in the present group in which 84% became anti HBs positive after vaccination. The safety of the fetus also was demonstrated, and no abnormal birth defect was observed. The stillbirths recorded occurred both in the vaccinated group and in the
Table V. Maternal groups
I
II III
controls from obstetric complications. As expected, passive transfer of ‘antibodies did occur following vaccination. However, the titres in this group were generally lower than in infants born to previously immunized mothers (Group II). This probably derives from the relatively higher titres of circulating antibodies in the latter group. Irrespective of the maternal group, anti HBs was rapidly cleared from the circulation of the infants. Protective levels of anti HBs were uncommonly detected after 2 months of age, and by 6 months the majority of the infants had little or no protection from maternal antibodies. It is therefore suggested that infants in endemic areas be vaccinated within 6 months of birth, and preferably before the age of 3 months. It was interesting to observe the relatively high incidence of HBV event in infants born to HBsAg positive mothers. This pattern was not only the consequence of vertical (motherchild) transmission [ 21 but also of horizontal (contact) transmission. This category of infants should therefore be considered for hepatitis vaccination much earlier than 3 months. Acknowledgment We thank Merck, Sharp and Dohme for providing some of the vaccines. We acknowledge the invaluable help of the midwives in the maternity centres and private hospitals. Mr. Debo Omoyele kindly provided the secretarial support.
HBsAg in infants born to the different groups. HBV markers (maternal status)
(a) Anti-HBs positive (vaccinated) (b) Anti-HBs negative (vaccinated) Anti-HBs positive (placebo) HBs positive (placebo)
Znt J Gynaecol Obstet 25
No. of infants
No. positive for HBsAg at Birth
1
3
6
12 (months)
61
0
0
0
1
2 (n = 54)
11
0
0
0
0
1 (n = 11)
65 21
0 9
0 5
0 3
1 3
1 (n = 61) 3 (n = 20)
Hepatitis B vaccine in pregnancy
References 1 Ayoola EA: The immune response of healthy Nigerian adults to small dose of hepatitis B vaccine. Comparison of 10 and 20 fig doses. J Med Vlrol13: 223,1984. 2 Ayoola EA, Ogunbode 0, Odelola HA: Congenital transmission of hepatitis B antigen in Nigerians. Arch Virol 67: 97, 1981. 3 Beasley RP, Hwang LY, Lin CC, Chien CB: Hepatocellular carcinoma and hepatitis B virus. A prospective study of 22707 men in Taiwan. Lancet ii: 1129,198l. 4 Blumberg BS, London WT: Hepatitis B virus and primary hepatocellular carcinoma: relationship of ICRONS to cancer. In: Viruses in Naturally Occurring Cancer (eds M Essex, G Tedero, H Zur Hausen), Cold Spring Harbor Conference on cell proliferation, Vol 7, pp 401-421 Cold Spring Harbor Laboratory, New York, 1980. 5 Hollinger FB, A&m I, Heiberg D, Melnick JL: Response to hepatitis B vaccine in a young adult population. In Viral Hepatitis (eds W Szmuness, HJ Alter, JE Maynard), pp 451-466. 6 Maupas P, Chiron JP, Goudeau A, Coursaget P, Perrin J, Barin F, Denis F, Diop-Mar I: Active immunization
301
against hepatitis B in an area of high endemicity. Part II: Prevention of early infection of the child. Prog Med Virol27: 188,198l. Szmuness W, Stevens CE, Harley EJ, Znak EA, Oleszko WR, William DC, Sadousky R, Morrison JM, Kellner A: Hepatitis B vaccine: demonstration of efficacy in a controlled clinical trial in a high risk population in the United States. N Engl. J Med 202: 883, 1980. Tong MJ, Thursby MW, Lin JH, Weissmann JY, Mcpeak CM: Studies on the maternal-infant transmission of the hepatitis B virus and HBV infection within families. Prog MedVirol27: 137,198l. William AO: Hepatitis B surface antigen and Liver cell carcinoma. Am J Med Sci270: 53,197s.
Address for reprints: Prof. E.A. Ayoola P.O. Box 7629 Secretariat P.O. Ibadan Nigeria
ZntJ Gynaecol Obstet 25