Fewer HPV vaccine doses may still prevent cervical cancer
MedWire News: Fewer than three doses of the bivalent human papillomavirus (HPV) vaccine may be as effective as the standard three-dose regimen for the prevention of cervical cancer, according to a study published in the Journal of the National Cancer Institute.
Aimée Kreimer (National Institutes of Health, Rockville, Maryland, USA) and colleagues explain that approximately 85% of cervical cancers occur in developing countries that do not have effective screening programs.
Administering HPV vaccines to women in these countries could reduce disease burden, but the current three-dose vaccine regimens are expensive and difficult to complete, especially in settings where the need for cervical cancer prevention is greatest, says the team.
To determine whether a lower number of doses of the Cervarix (GlaxoSmithKline Biologicals) bivalent HPV16/18 vaccine would be as effective as the full three doses, Kramer and team reviewed data from the Costa Rica Vaccine Trial, in which 7466 women aged 18 to 25 years were randomly assigned to receive either three doses of HPV vaccine or a control vaccine (hepatitis A).
During the trial, approximately 20% of the women received fewer than three doses of the vaccine - mainly due to pregnancy or referral to colposcopy - which enabled the researchers to compare the efficacy of fewer than three doses of the HPV vaccine with that of the standard regimen in the prevention of newly detected persistent (≥1 year) HPV16 and HPV18 infections.
After excluding women who had no follow-up or who were HPV16 and HPV18 DNA positive at enrollment, 5967 women received three vaccine doses (of whom 2957 received the HPV vaccine and 3010 received the control vaccine), 802 received two doses (422 HPV, 380 control), and 384 received one dose (196 HPV, 188 control).
The researchers report that the incidence of persistent HPV16 or HPV18 infections was similar among women who received three doses (4.4%), two doses (4.5%), or one dose (5.3%) of the control vaccine. This indicates that the women were at similar risk for acquiring HPV infections regardless of the number of doses received, says the team.
Importantly, during a median follow-up period of 4.2 years, vaccine efficacy against persistent HPV16 or HPV18 infection did not differ significantly among the groups, at 80.9%, 84.1%, and 100.0% for three doses, two doses, and one dose, respectively.
Kreimer and co-authors note that the protection afforded by a single dose of the vaccine was "unexpected" and will need further evaluation.
However, "if randomized studies and cost-effectiveness analyses confirm the benefits of administering fewer doses, and the duration of protection is sufficient, then the need for fewer doses may help make primary prevention of cervical cancer a reality," the team concludes.
In an accompanying editorial, Cosette Wheeler, from the University of New Mexico in Albuquerque, agreed that there is a need for additional, larger studies specifically designed to evaluate the efficacy of one, two, and three doses of the vaccine for adolescent girls.
However, "if it were possible to achieve high vaccine efficacy with fewer than three doses of HPV vaccine, more women could be vaccinated for the same cost, which could be particularly advantageous in low-resource settings," she said.
"In this context, the age old adage of less is more may apply to HPV vaccination and if so, the report of Kreimer et al represents an important step on the road to more effective and sustainable cervical cancer prevention programs."
By Laura Dean