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Meningococcal disease during the Hajj and Umrah mass gatherings: A, C, W, Y may be covered but don't forget the B and X factors!
Travel Medicine and Infectious Disease xxx (2017) 1e3
Contents lists available at ScienceDirect
Travel Medicine and Infectious Disease journal homepage: www.elsevierhealth.com/journals/tmid
Editorial
Meningococcal disease during the Hajj and Umrah mass gatherings: A, C, W, Y may be covered but don't forget the B and X factors!
Keywords: Meningococcal disease Hajj Mass gatherings Vaccine Neisseria meningitidis
Several papers in this issue of Travel Medicine and Infectious Disease address infectious and non-infectious disease risks for pilgrims visiting the Hajj. This editorial highlights another important risk namely, infection caused by Neisseria meningitidis. Due to the seriousness of the infection, its disabling sequelae, and the potential for epidemic spread, a single case of meningococcal disease elicits an urgent public health response. Asymptomatic carriers are the primary source of N. meningitidis transmissions although less than 1% of individuals who acquire carriage go on to develop meningococcal disease which results from the interplay of microbial, environmental and host factors [1]. Of the 12 serogroups of N. meningitidis identified, six (A, B, C, W, X, and Y) cause almost all invasive meningococcal disease worldwide [2]. The prevention of meningococcal disease is multifactorial but vaccination remains the most effective strategy [3]. There are currently vaccines available against 5 of the six main invasive meningococcal serogroups. Both polysaccharide and conjugate vaccines protecting against serogroups A, C, W and Y have been licensed and used for the prevention and control of the disease in mass vaccination campaigns or as part of the national childhood immunization programs in many countries [3,4]. Recently vaccines protecting against MenB disease (MenB-4C andrLP2086) have also been developed, licensed, and are used in a number of developing countries [4]. There is currently no vaccine to prevent against disease caused by MenX, although candidate vaccines are in development [4]. The Kingdom of Saudi Arabia annually hosts over 10 million Muslim pilgrims during the Hajj and Umrah mass gatherings [5]. This number is only going to rise in the coming years with the country aiming to increase the number of religious visitors to 30 million by 2030 for the Umrah mass gathering alone. Hajj and Umrah represent many of the risk factors for meningococcal disease and have historically been associated with both local and international outbreaks of the disease. These include MenA disease outbreaks in
1987 and throughout the 1990s and two international MenW outbreaks in 2000 and 2001 [1]. The implementation of strict preventative measures including mandatory meningococcal vaccination, targeted chemoprophylaxis, health awareness and educational campaigns, as well as an active disease surveillance and response system, has prevented pilgrimage-associated meningococcal outbreaks since 2001 [3]. The reduction in cases of meningococcal disease related to Hajj and Umrah has been so dramatic to the extent that in Mecca, the site of the pilgrimages, there has been no reported cases of the disease since 2006 [1]. The mandatory quadrivalent (A, C, Y, W) meningococcal vaccination for pilgrims does not specify a particular vaccine technology to be used, hence depending on the country, either polysaccharide or conjugate vaccine formulations are administered to pilgrims [3,5]. This means that the current Hajj and Umrah meningococcal disease preventative measures do not protect against MenB or MenX disease and do not necessarily prevent carriage and transmission due to the widespread use of polysaccharide vaccines. As a consequence, meningococcal disease remains a serious threat to these mass gatherings with the potential for local and international outbreaks among susceptible populations. Available data suggest that the incidence of meningococcal disease worldwide has decreased significantly [6], yet the threat remains. In Saudi Arabia, while there were no major outbreaks of meningococcal disease due to MenB or MenX, these serogroups have been reported to have caused disease among pilgrims and the Saudi population and were isolated from pilgrims in carriage studies [1,7]. This is particularly true for MenB. The latter causes the majority of meningococcal disease in European countries, particularly in countries that have introduced the MenC conjugate vaccines [6]. MenB also predominates in Australia, New Zealand and the Americas where outbreaks of the disease have been reported in recent years [2,6]. Though the proportion of Hajj and Umrah pilgrims from these regions is not significant, the predominance of MenB as the cause of meningococcal disease in these areas is a concern. In Turkey, one of the largest Muslim nations, available reports suggest that MenB is also a dominant cause of invasive disease as well as being commonly asymptomatically carried among the Turkish population [8,9]. MenX has also been reported to cause disease in the country [8]. Limited data are available on the meningococcal disease in the MENA region and South and Southeast Asia, which together represent the areas where most Hajj and Umrah pilgrims originate from, hence probably the most significant source of threat of meningococcal disease in these events. Nevertheless, available data indicates that MenB disease has been increasingly reported in these regions and the emergence of antibiotic-resistance in N. meningitidis in South
http://dx.doi.org/10.1016/j.tmaid.2017.02.001 1477-8939/© 2017 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Yezli S, Alotaibi BMeningococcal disease during the Hajj and Umrah mass gatherings: A, C, W, Y may be covered but don't forget the B and X factors!, Travel Medicine and Infectious Disease (2017), http://dx.doi.org/10.1016/j.tmaid.2017.02.001
2
Editorial / Travel Medicine and Infectious Disease xxx (2017) 1e3
Asia is particularly alarming [1,3]. Similarly, while chemoprophylaxis is mandatory for pilgrims originating from the sub-Saharan African meningitis belt, the emergence of MenX in the region is concerning [6]. Data on meningococcal disease in the rest of sub-Saharan Africa is limited and what is available suggest that in South Africa MenB is the most common cause of disease in recent years [10]. Given that chemoprophylaxis is not applicable for South African pilgrims, they could be a source of MenB in Hajj and Umrah. Additional source of threat is the extensive genetic exchange that occurs among N. meningitidis strains which generates a fluctuation in the molecular epidemiology that can lead to the development of hypervirulent or new and potentially pathogenic strains or threats of disease developing from serogroups already included in the current Hajj and Umrah required vaccines. N. meningitidis uses a variety of mechanisms to undergo antigenic variability, particularly in the face of natural or vaccine induced immunity. These include horizontal gene transfer, gene conversion, variable gene expression and phase variation [2]. One consequence of horizontal gene transfer in N. meningitidis is capsular switching, which is presumed to occur during co-colonization of the pharynx with two or more meningococcal strains, and allows N. meningitidis to change its capsular phenotype [2,11]. This mechanism can be very rapid and can be responsible for starting and sustaining meningococcal outbreaks by allowing immunologic escape from the original serogroup [2,11]. It is thought that capsular switching was at least partly responsible for the Hajj-related MenW outbreak of 2000 and the subsequent international spread of the endemic strain [2]. Capsular switching from various serogroups to MenB or MenX for instance have been reported including one case of serogroup C to B capsular switching that led to a fatal MenB disease [2,11]. A concern is that the current Hajj and Umrah compulsory quadrivalent vaccine policy could lead to an increase in meningococcal disease incidence or outbreaks due to strains not included in the vaccine or with those with reduced vaccine antigen expression. This could hypothetically occur through capsular switching or through serogroup replacement, whereby nonvaccine type organisms fill the niche vacated by the removal of vaccine-type strains [2]. One way of further reducing the risk of meningococcal disease during Hajj and Umrah is the introduction of compulsory vaccination with new vaccines to offer a wider protection against invasive serogroups. While no vaccine is yet developed to protect against MenX disease, vaccines for the prevention of MenB disease are available [4]. One of the key issues to be addressed is that there are still many scientific unknowns regarding these vaccines which are not easy to resolve given the low burden of MenB disease globally. These unknowns include the vaccines effectiveness and strain coverage give the high sequence variability of MenB strains, duration of protection and whether they provide herd immunity. For both vaccines, actual effectiveness and duration of protections are still unclear. Results of studies on the impact of MenB vaccines on carriage and subsequent herd protection are inconclusive [4]. Other points to consider are the elevated cost of these vaccines, their availability, the age groups these vaccines are licensed for and whether a single dose of the vaccine is enough to be protective. As international pilgrims need to be vaccinated before arrival to the Kingdom for Hajj or Umrah at their home countries, the cost and availability of the vaccines are important factors. A large majority of pilgrims originate from low income countries where these vaccines are not available or affordable. Cost and availability of vaccines is one reason why the current Hajj and Umrah
meningococcal vaccination requirements do not specify the more costly conjugate quadrivalent vaccine as the vaccine that needs to be administered to pilgrims, but instead polysaccharide or conjugate vaccines are accepted. While some countries licensed MenB vaccines for infants over 2 months old, in the USA both MenB-4C and rLP2086 vaccines are licensed for the age group 10e25 years old [4]. This is important given that the majority of the Hajj and Umrah pilgrims are over 25 and a large proportion of them are elderly. In addition MenB vaccines are administered in multiple doses [4] which would not be practical for the Hajj and Umrah pilgrims. Hence without addressing the above issues, the introduction of a requirement for vaccination with the current MenB vaccines for pilgrims is unlikely. In summary, despite the great success in the prevention of meningococcal disease at the Hajj and Umrah mass gatherings, the disease remains an important public health threat at these events. This is mainly due to the fact that the current Hajj and Umrah meningococcal disease preventative measures do not protect against all invasive serogroups such as MenB and MenX and do not necessarily affect carriage and transmission. As such, vigilance is required in the form of continued surveillance of meningococcal diseases nationally and globally, especially in countries with large Muslim populations, strict implementation of preventative measures for Hajj and Umrah which should be reviewed and updated in accordance with changes in the epidemiology of meningococcal disease and availability of new preventative tools. Due to the possibility of a rapid change in the epidemiology of meningococcal disease during Hajj and Umrah, contingency plans should be in place to contain outbreaks, which may include availability of MenB vaccines for mass vaccinations to control potential outbreaks. Conflict of interest statement The authors declare that there are no conflicts of interest.
References [1] Yezli S, Assiri AM, Alhakeem RF, Turkistani AM, Alotaibi B. Meningococcal disease during the Hajj and Umrah mass gatherings. Int J Infect Dis 2016;47: 60e4. [2] Harrison LH, Trotter CL, Ramsay ME. Global epidemiology of meningococcal disease. Vaccine 2009;27(Suppl 2):B51e63. [3] Yezli S, Bin Saeed AA, Assiri AM, Alhakeem RF, Yunus MA, Turkistani AM, et al. Prevention of meningococcal disease during the Hajj and Umrah mass gatherings: past and current measures and future prospects. Int J Infect Dis 2016;47: 71e8. [4] Piccini G, Torelli A, Gianchecchi E, Piccirella S, Montomoli E. Fighting Neisseria meningitidis: past and current vaccination strategies. Expert Rev Vaccines 2016:1e15. [5] Ahmed QA, Memish ZA. Hajj 2016: required vaccinations, crowd control, novel wearable tech and the Zika threat. Travel Med Infect Dis 2016;14: 429e32. [6] Pelton SI. The global evolution of meningococcal epidemiology following the introduction of meningococcal vaccines. J Adolesc Health 2016;59:S3e11. [7] Yezli S, Wilder-Smith A, Bin Saeed AA. Carriage of Neisseria meningitidis in the Hajj and Umrah mass gatherings. Int J Infect Dis 2016;47:65e70. [8] Toprak D, Soysal A, Torunoglu MA, Turgut M, Turkoglu S, Pimenta FC, et al. PCR-based national bacterial meningitis surveillance in Turkey: years 2006 to 2009. Pediatr Infect Dis J 2014;33:1087e9. [9] Kepenekli KE, Guneser MD, Soysal A, Karaaslan A, Atici S, Durmaz R, et al. Prevalence of Neisseria meningitidis carriage: a small-scale survey in Istanbul, Turkey. J Infect Dev Ctries 2016;10:413e7. [10] Sridhar S, Greenwood B, Head C, Plotkin SA, Safadi MA, Saha S, et al. Global incidence of serogroup B invasive meningococcal disease: a systematic review. Lancet Infect Dis 2015;15:1334e46. [11] Vogel U, Claus H, Frosch M. Rapid serogroup switching in Neisseria meningitidis. N Engl J Med 2000;342:219e20.
Please cite this article in press as: Yezli S, Alotaibi BMeningococcal disease during the Hajj and Umrah mass gatherings: A, C, W, Y may be covered but don't forget the B and X factors!, Travel Medicine and Infectious Disease (2017), http://dx.doi.org/10.1016/j.tmaid.2017.02.001
Editorial / Travel Medicine and Infectious Disease xxx (2017) 1e3
Saber Yezli, PhD*, Badriah Alotaibi, MPH The Global Centre for Mass Gatherings Medicine, Ministry of Health, Riyadh, Saudi Arabia
3
E-mail address: [email protected] (S. Yezli). 1 February 2017 Available online xxx
* Corresponding author. Global Centre for Mass Gatherings Medicine, Public Health Directorate, Ministry of Health, Riyadh, Saudi Arabia.
Please cite this article in press as: Yezli S, Alotaibi BMeningococcal disease during the Hajj and Umrah mass gatherings: A, C, W, Y may be covered but don't forget the B and X factors!, Travel Medicine and Infectious Disease (2017), http://dx.doi.org/10.1016/j.tmaid.2017.02.001
Contents lists available at ScienceDirect
Travel Medicine and Infectious Disease journal homepage: www.elsevierhealth.com/journals/tmid
Editorial
Meningococcal disease during the Hajj and Umrah mass gatherings: A, C, W, Y may be covered but don't forget the B and X factors!
Keywords: Meningococcal disease Hajj Mass gatherings Vaccine Neisseria meningitidis
Several papers in this issue of Travel Medicine and Infectious Disease address infectious and non-infectious disease risks for pilgrims visiting the Hajj. This editorial highlights another important risk namely, infection caused by Neisseria meningitidis. Due to the seriousness of the infection, its disabling sequelae, and the potential for epidemic spread, a single case of meningococcal disease elicits an urgent public health response. Asymptomatic carriers are the primary source of N. meningitidis transmissions although less than 1% of individuals who acquire carriage go on to develop meningococcal disease which results from the interplay of microbial, environmental and host factors [1]. Of the 12 serogroups of N. meningitidis identified, six (A, B, C, W, X, and Y) cause almost all invasive meningococcal disease worldwide [2]. The prevention of meningococcal disease is multifactorial but vaccination remains the most effective strategy [3]. There are currently vaccines available against 5 of the six main invasive meningococcal serogroups. Both polysaccharide and conjugate vaccines protecting against serogroups A, C, W and Y have been licensed and used for the prevention and control of the disease in mass vaccination campaigns or as part of the national childhood immunization programs in many countries [3,4]. Recently vaccines protecting against MenB disease (MenB-4C andrLP2086) have also been developed, licensed, and are used in a number of developing countries [4]. There is currently no vaccine to prevent against disease caused by MenX, although candidate vaccines are in development [4]. The Kingdom of Saudi Arabia annually hosts over 10 million Muslim pilgrims during the Hajj and Umrah mass gatherings [5]. This number is only going to rise in the coming years with the country aiming to increase the number of religious visitors to 30 million by 2030 for the Umrah mass gathering alone. Hajj and Umrah represent many of the risk factors for meningococcal disease and have historically been associated with both local and international outbreaks of the disease. These include MenA disease outbreaks in
1987 and throughout the 1990s and two international MenW outbreaks in 2000 and 2001 [1]. The implementation of strict preventative measures including mandatory meningococcal vaccination, targeted chemoprophylaxis, health awareness and educational campaigns, as well as an active disease surveillance and response system, has prevented pilgrimage-associated meningococcal outbreaks since 2001 [3]. The reduction in cases of meningococcal disease related to Hajj and Umrah has been so dramatic to the extent that in Mecca, the site of the pilgrimages, there has been no reported cases of the disease since 2006 [1]. The mandatory quadrivalent (A, C, Y, W) meningococcal vaccination for pilgrims does not specify a particular vaccine technology to be used, hence depending on the country, either polysaccharide or conjugate vaccine formulations are administered to pilgrims [3,5]. This means that the current Hajj and Umrah meningococcal disease preventative measures do not protect against MenB or MenX disease and do not necessarily prevent carriage and transmission due to the widespread use of polysaccharide vaccines. As a consequence, meningococcal disease remains a serious threat to these mass gatherings with the potential for local and international outbreaks among susceptible populations. Available data suggest that the incidence of meningococcal disease worldwide has decreased significantly [6], yet the threat remains. In Saudi Arabia, while there were no major outbreaks of meningococcal disease due to MenB or MenX, these serogroups have been reported to have caused disease among pilgrims and the Saudi population and were isolated from pilgrims in carriage studies [1,7]. This is particularly true for MenB. The latter causes the majority of meningococcal disease in European countries, particularly in countries that have introduced the MenC conjugate vaccines [6]. MenB also predominates in Australia, New Zealand and the Americas where outbreaks of the disease have been reported in recent years [2,6]. Though the proportion of Hajj and Umrah pilgrims from these regions is not significant, the predominance of MenB as the cause of meningococcal disease in these areas is a concern. In Turkey, one of the largest Muslim nations, available reports suggest that MenB is also a dominant cause of invasive disease as well as being commonly asymptomatically carried among the Turkish population [8,9]. MenX has also been reported to cause disease in the country [8]. Limited data are available on the meningococcal disease in the MENA region and South and Southeast Asia, which together represent the areas where most Hajj and Umrah pilgrims originate from, hence probably the most significant source of threat of meningococcal disease in these events. Nevertheless, available data indicates that MenB disease has been increasingly reported in these regions and the emergence of antibiotic-resistance in N. meningitidis in South
http://dx.doi.org/10.1016/j.tmaid.2017.02.001 1477-8939/© 2017 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Yezli S, Alotaibi BMeningococcal disease during the Hajj and Umrah mass gatherings: A, C, W, Y may be covered but don't forget the B and X factors!, Travel Medicine and Infectious Disease (2017), http://dx.doi.org/10.1016/j.tmaid.2017.02.001
2
Editorial / Travel Medicine and Infectious Disease xxx (2017) 1e3
Asia is particularly alarming [1,3]. Similarly, while chemoprophylaxis is mandatory for pilgrims originating from the sub-Saharan African meningitis belt, the emergence of MenX in the region is concerning [6]. Data on meningococcal disease in the rest of sub-Saharan Africa is limited and what is available suggest that in South Africa MenB is the most common cause of disease in recent years [10]. Given that chemoprophylaxis is not applicable for South African pilgrims, they could be a source of MenB in Hajj and Umrah. Additional source of threat is the extensive genetic exchange that occurs among N. meningitidis strains which generates a fluctuation in the molecular epidemiology that can lead to the development of hypervirulent or new and potentially pathogenic strains or threats of disease developing from serogroups already included in the current Hajj and Umrah required vaccines. N. meningitidis uses a variety of mechanisms to undergo antigenic variability, particularly in the face of natural or vaccine induced immunity. These include horizontal gene transfer, gene conversion, variable gene expression and phase variation [2]. One consequence of horizontal gene transfer in N. meningitidis is capsular switching, which is presumed to occur during co-colonization of the pharynx with two or more meningococcal strains, and allows N. meningitidis to change its capsular phenotype [2,11]. This mechanism can be very rapid and can be responsible for starting and sustaining meningococcal outbreaks by allowing immunologic escape from the original serogroup [2,11]. It is thought that capsular switching was at least partly responsible for the Hajj-related MenW outbreak of 2000 and the subsequent international spread of the endemic strain [2]. Capsular switching from various serogroups to MenB or MenX for instance have been reported including one case of serogroup C to B capsular switching that led to a fatal MenB disease [2,11]. A concern is that the current Hajj and Umrah compulsory quadrivalent vaccine policy could lead to an increase in meningococcal disease incidence or outbreaks due to strains not included in the vaccine or with those with reduced vaccine antigen expression. This could hypothetically occur through capsular switching or through serogroup replacement, whereby nonvaccine type organisms fill the niche vacated by the removal of vaccine-type strains [2]. One way of further reducing the risk of meningococcal disease during Hajj and Umrah is the introduction of compulsory vaccination with new vaccines to offer a wider protection against invasive serogroups. While no vaccine is yet developed to protect against MenX disease, vaccines for the prevention of MenB disease are available [4]. One of the key issues to be addressed is that there are still many scientific unknowns regarding these vaccines which are not easy to resolve given the low burden of MenB disease globally. These unknowns include the vaccines effectiveness and strain coverage give the high sequence variability of MenB strains, duration of protection and whether they provide herd immunity. For both vaccines, actual effectiveness and duration of protections are still unclear. Results of studies on the impact of MenB vaccines on carriage and subsequent herd protection are inconclusive [4]. Other points to consider are the elevated cost of these vaccines, their availability, the age groups these vaccines are licensed for and whether a single dose of the vaccine is enough to be protective. As international pilgrims need to be vaccinated before arrival to the Kingdom for Hajj or Umrah at their home countries, the cost and availability of the vaccines are important factors. A large majority of pilgrims originate from low income countries where these vaccines are not available or affordable. Cost and availability of vaccines is one reason why the current Hajj and Umrah
meningococcal vaccination requirements do not specify the more costly conjugate quadrivalent vaccine as the vaccine that needs to be administered to pilgrims, but instead polysaccharide or conjugate vaccines are accepted. While some countries licensed MenB vaccines for infants over 2 months old, in the USA both MenB-4C and rLP2086 vaccines are licensed for the age group 10e25 years old [4]. This is important given that the majority of the Hajj and Umrah pilgrims are over 25 and a large proportion of them are elderly. In addition MenB vaccines are administered in multiple doses [4] which would not be practical for the Hajj and Umrah pilgrims. Hence without addressing the above issues, the introduction of a requirement for vaccination with the current MenB vaccines for pilgrims is unlikely. In summary, despite the great success in the prevention of meningococcal disease at the Hajj and Umrah mass gatherings, the disease remains an important public health threat at these events. This is mainly due to the fact that the current Hajj and Umrah meningococcal disease preventative measures do not protect against all invasive serogroups such as MenB and MenX and do not necessarily affect carriage and transmission. As such, vigilance is required in the form of continued surveillance of meningococcal diseases nationally and globally, especially in countries with large Muslim populations, strict implementation of preventative measures for Hajj and Umrah which should be reviewed and updated in accordance with changes in the epidemiology of meningococcal disease and availability of new preventative tools. Due to the possibility of a rapid change in the epidemiology of meningococcal disease during Hajj and Umrah, contingency plans should be in place to contain outbreaks, which may include availability of MenB vaccines for mass vaccinations to control potential outbreaks. Conflict of interest statement The authors declare that there are no conflicts of interest.
References [1] Yezli S, Assiri AM, Alhakeem RF, Turkistani AM, Alotaibi B. Meningococcal disease during the Hajj and Umrah mass gatherings. Int J Infect Dis 2016;47: 60e4. [2] Harrison LH, Trotter CL, Ramsay ME. Global epidemiology of meningococcal disease. Vaccine 2009;27(Suppl 2):B51e63. [3] Yezli S, Bin Saeed AA, Assiri AM, Alhakeem RF, Yunus MA, Turkistani AM, et al. Prevention of meningococcal disease during the Hajj and Umrah mass gatherings: past and current measures and future prospects. Int J Infect Dis 2016;47: 71e8. [4] Piccini G, Torelli A, Gianchecchi E, Piccirella S, Montomoli E. Fighting Neisseria meningitidis: past and current vaccination strategies. Expert Rev Vaccines 2016:1e15. [5] Ahmed QA, Memish ZA. Hajj 2016: required vaccinations, crowd control, novel wearable tech and the Zika threat. Travel Med Infect Dis 2016;14: 429e32. [6] Pelton SI. The global evolution of meningococcal epidemiology following the introduction of meningococcal vaccines. J Adolesc Health 2016;59:S3e11. [7] Yezli S, Wilder-Smith A, Bin Saeed AA. Carriage of Neisseria meningitidis in the Hajj and Umrah mass gatherings. Int J Infect Dis 2016;47:65e70. [8] Toprak D, Soysal A, Torunoglu MA, Turgut M, Turkoglu S, Pimenta FC, et al. PCR-based national bacterial meningitis surveillance in Turkey: years 2006 to 2009. Pediatr Infect Dis J 2014;33:1087e9. [9] Kepenekli KE, Guneser MD, Soysal A, Karaaslan A, Atici S, Durmaz R, et al. Prevalence of Neisseria meningitidis carriage: a small-scale survey in Istanbul, Turkey. J Infect Dev Ctries 2016;10:413e7. [10] Sridhar S, Greenwood B, Head C, Plotkin SA, Safadi MA, Saha S, et al. Global incidence of serogroup B invasive meningococcal disease: a systematic review. Lancet Infect Dis 2015;15:1334e46. [11] Vogel U, Claus H, Frosch M. Rapid serogroup switching in Neisseria meningitidis. N Engl J Med 2000;342:219e20.
Please cite this article in press as: Yezli S, Alotaibi BMeningococcal disease during the Hajj and Umrah mass gatherings: A, C, W, Y may be covered but don't forget the B and X factors!, Travel Medicine and Infectious Disease (2017), http://dx.doi.org/10.1016/j.tmaid.2017.02.001
Editorial / Travel Medicine and Infectious Disease xxx (2017) 1e3
Saber Yezli, PhD*, Badriah Alotaibi, MPH The Global Centre for Mass Gatherings Medicine, Ministry of Health, Riyadh, Saudi Arabia
3
E-mail address: [email protected] (S. Yezli). 1 February 2017 Available online xxx
* Corresponding author. Global Centre for Mass Gatherings Medicine, Public Health Directorate, Ministry of Health, Riyadh, Saudi Arabia.
Please cite this article in press as: Yezli S, Alotaibi BMeningococcal disease during the Hajj and Umrah mass gatherings: A, C, W, Y may be covered but don't forget the B and X factors!, Travel Medicine and Infectious Disease (2017), http://dx.doi.org/10.1016/j.tmaid.2017.02.001