One Dose of HPV Vaccine Works As Well As Two

Human papillomavirus (HPV) infection is the main cause of cervical cancer worldwide, and HPV vaccines are highly effective at preventing the high-risk virus types responsible for most cases. Despite this, HPV vaccination remains underused globally, partly because the recommended multidose schedule can be difficult to deliver, especially in low-resource settings. Emerging evidence suggests that a single dose may provide strong protection, but it has been unclear whether one dose works as well as the standard two-dose regimen. To answer this question, scientists in this 2025 study used a noninferiority trial design, which tests whether a certain intervention (e.g. one dose) is not meaningfully worse than the standard approach (e.g. two doses).

In this large randomized trial, more than 20,000 girls aged 12 to 16 were divided into four groups, and assigned to receive either one or two doses of a bivalent HPV vaccine (protecting against HPV types 16 and 18) or one or two doses of a nonavalent vaccine (protecting against nine HPV types). Participants were followed for up to five years, and researchers measured new HPV16 or HPV18 infections that lasted at least six months. Vaccine protection was also compared with infection rates among about 3,000 unvaccinated girls and young women from a separate survey.

The study found that one dose was not inferior to two doses in preventing HPV16 or HPV18 infection for either vaccine. Infection rates were very similar across one- and two-dose groups, and vaccine effectiveness was at least 97% in all vaccinated groups compared with unvaccinated participants. No safety concerns were identified.

Overall, the findings show that a single dose of either a bivalent or nonavalent HPV vaccine provided strong protection against key cancer-causing HPV types and performed as well as two doses over the study period.