Incremental benefits of male HPV vaccination: accounting for inequality in population uptake.

backgroundVaccines against HPV16/18 are approved for use in females and males but most countries currently have female-only programs. Cultural and geographic factors associated with HPV vaccine uptake might also influence sexual partner choice; this might impact post-vaccination outcomes. Our aims were to examine the population-level impact of adding males to HPV vaccination programs if factors influencing vaccine uptake also influence partner choice, and additionally to quantify how this changes the post-vaccination distribution of disease between subgroups, using incident infections as the outcome measure.

methodsA dynamic model simulated vaccination of pre-adolescents in two scenarios: 1) vaccine uptake was correlated with factors which also affect sexual partner choice ("correlated"); 2) vaccine uptake was unrelated to these factors ("unrelated"). Coverage and degree of heterogeneity in uptake were informed by observed data from Australia and the USA. Population impact was examined via the effect on incident HPV16 infections. The rate ratio for post-vaccination incident HPV16 in the lowest compared to the highest coverage subgroup (RR(L)) was calculated to quantify between-group differences in outcomes.

resultsThe population-level incremental impact of adding males was lower if vaccine uptake was "correlated", however the difference in population-level impact was extremely small (<1%) in the Australia and USA scenarios, even under the conservative and extreme assumption that subgroups according to coverage did not mix at all sexually. At the subgroup level, "correlated" female-only vaccination resulted in RR(L)= 1.9 (Australia) and 1.5 (USA) in females, and RR(L)= 1.5 and 1.3 in males. "Correlated" both-sex vaccination increased RR(L) to 4.2 and 2.1 in females and 3.9 and 2.0 in males in the Australia and USA scenarios respectively.

conclusionsThe population-level incremental impact of male vaccination is unlikely to be substantially impacted by feasible levels of heterogeneity in uptake. However, these findings emphasize the continuing importance of prioritizing high coverage across all groups in HPV vaccination programs in terms of achieving equality of outcomes.