One dose of the human papillomavirus (HPV) vaccine, which helps protect against cervical cancer and genital warts, may be sufficient to provide long-term protection from the sexually transmitted infection, a new study suggests. The vaccine is currently given in three separate doses and is recommended for nearly everyone between the ages of 9 and 26.
The study, published in Cancer Prevention Research and sponsored by the National Institutes of Health, found that women who received only one shot instead of all three still had sufficient levels of antibodies to protect against the most dangerous forms of the virus four years later. This finding could potentially make getting the vaccine cheaper and simpler, hopefully expanding the number of people worldwide who could receive the potentially life-saving vaccine.
HPV is estimated to infect 79 million Americans, and nearly all sexually active people are exposed to at least one of the 40 different sexually transmitted strains at some point. In many people, the virus is cleared from the body and does not cause disease, but in others it may go on to cause genital warts or cancer of the throat, cervix, vulva, vagina, penis or anus. Strains 16 and 18, which are both covered by the vaccine, are estimated to cause about 70% of cervical cancer cases. There are currently two varieties of the vaccine, and both are given in three doses over a six month period.
In the study, researchers gave women in Costa Rica either one, two or three doses of one type of the vaccine. The women who received two or three doses both had about the same levels of antibodies up to four years later. Women who received only one had lower levels, but they were still high enough to confer protection and they remained consistent over a four year period. Antibody levels in all the vaccinated women were much higher than those in people who had been exposed but never vaccinated. However, further study would be required before changes in vaccine regimens would be officially made.