Bivalent HPV vaccine efficacy may be independent of dose

By Shreeya Nanda, Senior medwireNews Reporter

Fewer than three doses of the bivalent human papillomavirus (HPV) vaccine may be sufficient to offer adequate protection against cervical HPV-16 and -18 infection, research published in The Lancet Oncology indicates.

“Our findings question the number of HPV vaccine doses truly needed to protect the majority of women against cervical cancer, and suggest that a one-dose schedule should be further evaluated”, said the study’s joint lead author Aimée Kreimer (National Cancer Institute, Bethesda, Maryland, USA) in a press release.

“If one dose is sufficient, it could reduce vaccination and administration costs as well as improve uptake. This is especially important in less developed regions of the world where more than 80% of cervical cancer cases occur.”

This post-hoc analysis used data from the phase III CVT and PATRICIA trials in which women aged between 15 and 25 years old were randomly assigned to receive either three doses of the HPV-16/18 AS04-adjuvanted vaccine or a control hepatitis A vaccine. However, a number of participants did not receive all three doses for various reasons, including pregnancy and colposcopy referral.

Among women who tested negative for HPV-16 and -18 DNA at intake, 22,327, 1185 and 543 women received three doses (11,110 HPV vs 11,217 control), two doses (611 HPV vs 574 control) and a single dose (292 HPV vs 251 control), respectively.

After a mean follow-up of 47.6 months, vaccine efficacy against one-time detection of incident HPV-16 and -18 infections for three doses was 77.0%. This compared with an efficacy of 76.0% and 85.7% for the two-dose and one-dose schedule, respectively, with no significant difference in efficacy between the groups.

Vaccine efficacy against incident HPV-16 and -18 infections that persisted for a minimum 6 and 12 months was 89.1% and 87.0%, respectively, among participants who received three doses. The corresponding rates were 89.7% and 89.6% among women who received two doses and 96.6% and 95.1% among those who received one dose.

In an accompanying commentary, Julia Brotherton (VCS Registries, East Melbourne, Victoria, Australia) stresses the importance of this finding, as strong vaccine efficacy against persistent infection is “a recommended outcome measure for assessment of protection in prophylactic HPV vaccine trials”.

She concludes: “These data suggest that one dose of bivalent HPV vaccine might be adequate to protect against HPV-16 and HPV-18 persistent infections and, therefore, probably disease.”

Kreimer et al also evaluated cross-protective efficacy and found that vaccine efficacy against one-time detection of incident HPV-31, -33 and -45 infections was 59.7%, 37.7% and 36.6% for three, two and one dose, respectively. And two doses given 6 months, but not 1 month, apart provided comparable partial protection to three doses.

The study authors are aware that their study findings are insufficient evidence to instigate an immediate change to vaccination scheduling, but they urge that “these new data argue strongly for additional assessments of this question.”

“Long-term population-effectiveness studies of girls vaccinated at young ages will be informative, but trials to directly investigate the vaccine efficacy of one dose will be necessary to motivate policy change”, the researchers conclude.

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