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Extending catch-up cohort for vaccine reduces HPV prevalence
In countries where HPV vaccination was previously targeted only to one or two cohorts of girls, an extended catch-up strategy targeting girls and boys appeared to expedite the relative reduction in HPV prevalence, according to recent data.
To examine the impact of alternative HPV vaccination strategies, researchers used a population-based, single-type model that accounted for the existence of men and women susceptible to, infected with and immune to HPV infection. The model’s output was fitted to age-specific curves of cervical HPV prevalence data obtained from cases tested through the Swedish Chlamydia trachomatis screening between March 2008 and November 2008.
The researchers evaluated four vaccination options, including the current Swedish program. Strategy 1 was modeled as routine vaccination of girls aged 11 years with vaccination of girls aged 12 years at 80.5% coverage, and a catch-up initiative aimed at vaccinating girls aged 13 to 18 years at 53.2% in the first year. Strategy 2 was routine vaccination of school-age girls combined with an extended, one-time catch-up of women aged 22 to 26 years in 2015. Strategy 3 added routine vaccination of school-age boys and an extended one-time catch-up of girls, and strategy 4 consisted of routine vaccination of school-age boys and an extended one-time catch-up of boys and girls.
During the first 10 years after vaccination, the extended catch-up led to a relative reduction in HPV prevalence of 49.4% (strategies 2 and 3) for girls and 55.6% (strategy 4) for boys, compared with the current program that provides a relative reduction of 38.6%. This increase in prevalence reduction resulting from catch-up persisted for approximately 30 years. Routine male vaccination was 7.2 times more resilient to coverage reduction than female-only vaccination, and male catch-up was 12.6-fold more resistant to coverage reduction than female-only catch-up.
The researchers concluded that the extension of the catch-up cohorts’ targeted vaccination may speed the relative reduction in HPV prevalence in women.
“If vaccination coverage is high, 25 to 30 years after vaccination commences, the effectiveness converges,” the researchers wrote. “The most salient impact of male vaccination is the mitigation of loss of vaccine effectiveness in the face of an unexpected reduction in coverage. The resilience to temporary changes in vaccination coverage of strategies that included male vaccination is likely to be crucial to safely adopt HPV-based cancer prevention programs with robust long-term effectiveness.” – by Jen Byrne
Disclosure: Elfström reports no relevant financial disclosures. Please see the full study for a list of all other authors’ relevant financial disclosures.