The findings stem from an analysis of data from the National Cancer Institute’s Costa Rica Vaccine Trial, in which 7,466 women were enrolled, according to a news release from the Journal of the National Cancer Institute, which published the results on Thursday.
The women were either given the HPV vaccine Cervarix or a Hepatitis A vaccine. Although researchers intended to give the women receiving Cervarix the full three doses, 20 percent of them got only one dose or two doses for a variety of reasons.
After four years, the researchers found, two doses of Cervarix offered the same level of protection against HPV infection as three. Even one dose offered a high level of protection.