HPV vaccine is effective even when all girls and boys are not vaccinated
Over 30,000 12-15-year-old Finnish girls and boys participated in a community-randomised trial that evaluated the impact of gender neutral vs. girls-only HPV16/18-vaccination in two school years: 2007/2008 and 2008/2009 in 33 municipalities. To evaluate the occurrence of HPV infections pre- and post-vaccination, antibodies against 16 HPV types were measured in serum samples from women aged 22 years and younger living in these municipalities between 2005 and 2016. A total of 8,000 samples from women were obtained from the Finnish Maternity Cohort.
This provided a reliable picture of the prevalence of HPV infections before and after the studied vaccination programme options (girls and boys, girls only, none) in the studied communities. The effectiveness of the options has only been studied in Finland. The Finnish Institute for Health and Welfare used the results when it drafted the recommendation to start the HPV vaccination programme for boys and girls in autumn 2020.
In communities where 20–30% of boys and 50% of girls were vaccinated, the prevalence of HPV16/18 virus types was also reduced due to the herd immunity among unvaccinated girls of the same age. In communities where only girls received the HPV vaccine, no herd immunity emerged, and the prevalence of HPV infections in the unvaccinated did not differ from the control sites where the subjects received a vaccine against the hepatitis B virus.
“A HPV vaccination programme can eradicate cancer-causing viruses from the young adult population thanks to herd immunity. Herd immunity against sexually transmitted infections is created even with low vaccination coverage,” says Matti Lehtinen, a visiting researcher at the Karolinska Institutet in Sweden, who was responsible for the study.
“The studies also showed that the elimination of HPV cancers among those who are not vaccinated for whatever reason is only possible if both girls and boys are vaccinated,” he adds.
Human papillomavirus seroprevalence in pregnant women following gender-neutral and girls-only vaccination programs in Finland: A cross-sectional cohort analysis following a cluster randomized trial by Penelope Gray and co-workers, PLoS Med 2021 Jun 7;18(6):e1003588.
Long-term of HPV type-replacement among young pregnant Finnish females before and after a community randomised HPV vaccination trial with moderate coverage by Penelope Gray and co-workers, Int J Cancer 147:3511-3522, 2020.
Matti Lehtinen, Karolinska Institutet, Stockholm, Sweden, and FICAN-Mid/Tampere University, Tampere, Finland matti.lehtinen [at] tuni.fi
Picture: Jonne Renvall