Fewer than 3 doses of HPV vaccine still effective

Two doses of the human papillomavirus (HPV) vaccine appeared to protect women against infection as well as the recommended three doses, a recent study found.

Researchers in Costa Rica evaluated the efficacy of fewer than three doses of the Cervarix HPV 16/18 vaccine as part of a larger study testing the vaccine against a control hepatitis A vaccine. The majority of the women in the study (2,957 in the HPV group and 3,010 controls) received three doses. For various reasons, the most common being pregnancy and colposcopy, the remaining women received only one or two doses. In total, 802 women (422 HPV and 380 control) got two shots and 384 (196 HPV and 188 control) only got one. The participants were followed for a median of 4.2 years to see if they developed HPV 16 or 18 infections that persisted for 10 months or more.

The study found that the efficacy of the HPV vaccine was 80.9% in those who received three doses (95% CI, 71.1% to 87.7%) compared to 84.1% in the two-dose group (95% CI, 50.2% to 96.3%) and 100% in the participants getting one dose (95% CI, 66.5% to 100%). The study authors concluded that two doses, and possibly even one dose, of the vaccine may be as protective as three doses. The results were published online Sept. 9 in the Journal of the National Cancer Institute.

The authors did note some limitations of the results, including that three doses appeared to offer greater cross-protection against other HPV types than the other regimens, although the differences were not statistically significant. The duration of protection also remains to be seen, as well as the applicability to other populations, since the trial population was largely comprised of sexually active women age 18 to 25 years.

An accompanying editorial called for additional research addressing larger populations and disease end points such as cervical intraepithelial neoplasia grade 3 or higher. If this study's findings are confirmed, using fewer doses could allow more women to be vaccinated, especially in the low-resource settings where cervical cancer causes the greatest disease burden, the editorialist concluded.