Sex-specific immunization for sexually transmitted infections such as human papillomavirus: insights from mathematical models.
BACKGROUND
Sex-specific differences regarding the transmissibility and the course of infection are the rule rather than the exception in the epidemiology of sexually transmitted infections (STIs). Human papillomavirus (HPV) provides an example: disease outcomes differ between men and women, as does the potential for transmission to the opposite sex. HPV vaccination of preadolescent girls was recently introduced in many countries, and inclusion of boys in the vaccination programs is being discussed. Here, we address the question of whether vaccinating females only, males only, or both sexes is the most effective strategy to reduce the population prevalence of an STI like HPV.


RESULTS
We use a range of two-sex transmission models with varying detail to identify general criteria for allocating a prophylactic vaccine between both sexes. The most effective reduction in the population prevalence of infection is always achieved by single-sex vaccination; vaccinating the sex with the highest prevaccine prevalence is the preferred strategy in most circumstances. Exceptions arise only when the higher prevaccine prevalence is due to a substantially lower rate of natural immunity, or when natural immunity is lifelong, and a prolonged duration of infectiousness coincides with increased transmissibility. Predictions from simple models were confirmed in simulations based on an elaborate HPV transmission model. Our analysis suggests that relatively inefficient genital transmission from males to females might render male vaccination more effective in reducing overall infection levels. However, most existing HPV vaccination programs have achieved sufficient coverage to continue with female-only vaccination.


CONCLUSIONS
Increasing vaccine uptake among preadolescent girls is more effective in reducing HPV infection than including boys in existing vaccination programs. As a rule, directing prophylactic immunization at the sex with the highest prevaccine prevalence results in the largest reduction of the population prevalence.
Department of Epidemiology and Biostatistics, VU University Medical Center, Amsterdam, The Netherlands. j.bogaards@vumc.nl
Johannes A
JA
Bogaards
Mirjam
M
Kretzschmar
Maria
M
Xiridou
Chris J L M
CJ
Meijer
Johannes
J
Berkhof
Jacco
J
Wallinga
D005260:Female; D006801:Humans; D007114:Immunization / Q000379:methods*; D008297:Male; D008962:Models, Theoretical; D027383:Papillomaviridae / Q000472:pathogenicity*; D030361:Papillomavirus Infections / Q000453:epidemiology / Q000503:physiopathology / Q000517:prevention & control* / Q000635:transmission; D053918:Papillomavirus Vaccines / Q000627:therapeutic use*; D012737:Sex Factors; D015229:Sexually Transmitted Diseases, Viral / Q000453:epidemiology / Q000503:physiopathology / Q000517:prevention & control* / Q000635:transmission; D002583:Uterine Cervical Neoplasms / Q000517:prevention & control / Q000821:virology
D053918:Papillomavirus Vaccines