Two doses of the HPV vaccine Cervarix may be just as effective as the recommended three-dose sequence, according to results of a clinical trial in Costa Rica.
Two doses of the human papillomavirus (HPV) vaccine Cervarix may be just as effective as the recommended three-dose sequence, finds a study published online last Friday in the Journal of the National Cancer Institute. The results were based on analysis of data from a clinical trial in Costa Rica by researchers at the National Cancer Institute and colleagues.
Each year, about 500,000 new cases of cervical cancer are diagnosed around the world—almost all of them caused by HPV infection—and 250,000 women die from the disease. Cervarix is one of two FDA-approved HPV vaccines, though the other one, Gardasil, is more commonly used in the US. (Gardasil protects against HPV 6, 11, 16, and 18, while Cervarix only protects against HPV 16 and 18.)
The standard regimen for both vaccines is three doses administered over six months, but cost and logistical challenges pose hurdles to adherence. This problem is particularly acute in poorer countries, but is also apparent in the US, where data from the Centers for Disease Control and Prevention found that in 2010, just 49% of girls aged 13 to 17 had received at least one dose of HPV vaccine and just 32% had received three doses.
In the Costa Rica trial, women aged 18 to 25 received either the HPV vaccine or the Hepatitis A vaccine as a control. The intent was to administer three doses of the HPV vaccine to those in the experimental group, but around a fifth of participants received just one or two doses. After four years of follow-up, those who had received two doses demonstrated the same resistance to infection with HPV 16 and 18 as those who had received three doses. Those who received just one dose also demonstrated a high level of resistance, though the researchers caution that a single dose is unlikely to confer long-term protection.
“Our study provides evidence that an HPV vaccine program using two doses will work,” said Aimée R. Kreimer, PhD, lead author and investigator in NCI’s Division of Cancer Epidemiology and Genetics, in a press release. “It may be that vaccinating more women, with fewer doses for each, will reduce cervical cancer incidence more than a standard three-dose program that vaccinates fewer women.”
The results may not carry over to Gardasil, because its formulation is different from that of Cervarix.
NIH study finds two doses of HPV vaccine may be as protective as full course [National Cancer Institute Press Release]
Proof-of-Principle Evaluation of the Efficacy of Fewer Than Three Doses of a Bivalent HPV16/18 Vaccine (abstract) [Journal of the National Cancer Institute]