By John Gever, Senior Editor, MedPage Today
Published: September 08, 2011
Reviewed by Dori F. Zaleznik, MD; Associate Clinical Professor of Medicine, Harvard Medical School, Boston.
Two doses of a bivalent vaccine against human papillomavirus (HPV) appeared just as effective in preventing persistent infections as the recommended three doses in young women, according to a study in Costa Rica.
In fact, the study — led by researchers at the U.S. National Cancer Institute — found that a single dose was effective as well, although the number of participants in that arm was relatively small.
The findings were important because, in low-income regions, providing the full three-dose regimen of HPV vaccines to all eligible women and teens may not be economically feasible, explained Aimée R. Kreimer, PhD, of the NCI’s epidemiology division in Rockville, Md., and colleagues.
“The cost and logistical difficulties of the standard three-dose vaccine regimen compromises implementation of this life-saving measure in resource-poor settings,” the researchers wrote online in the Journal of the National Cancer Institute.
“Our clinical efficacy data provide suggestive evidence that an HPV vaccine program that could vaccinate 50% more women with a two-dose regimen could potentially reduce cervical cancer incidence more than a standard three-dose program that uses the same number of total doses but in fewer women.”
The study was designed as a randomized trial involving nearly 7,500 women, who were to receive either three doses of the bivalent Cervarix vaccine active against HPV serotypes 16 and 18 or a hepatitis A vaccine that served as a control.
Participants were women 18 to 25 years old in general good health, HPV-negative at baseline according to liquid cytology and molecular testing, had no history of hepatitis A infection or vaccination, and were willing to use contraception during the vaccination period.
But some participants missed scheduled doses — 929 ended up receiving only two doses and 551 had just one dose.
About half of both groups had received active HPV vaccine and half had the control product. Outcomes were tracked in these women as they were in those receiving the full three-dose regimen.
The primary outcome measure was infection with HPV 16 or 18 that lasted as least 10 months. Participants were followed for a median of 4.2 years.
HPV vaccine efficacy rates by this measure were as follows:
- Three doses: 80.9% (95% CI 71.1% to 87.7%)
- Two doses: 84.1% (95% CI 50.2% to 96.3%)
- One dose: 100% (95% CI 66.5% to 100%)