A new study of women in Costa Rica finds that one dose of the human papillomavirus (HPV) vaccine may be enough to create the antibodies needed to prevent infection. If confirmed, this could be good news for people in the United States and abroad.
The study, funded by the U.S. National Cancer Institute and published in the November issue of Cancer Prevention Research, enrolled 503 Costa Ricans who fell into four categories. Some of the women (113) had antibodies to HPV because they had been infected with the virus. The others had received doses of the HPV vaccine Cervarix—78 of them had received just one dose, 192 had received two doses, and 120 had received all three.
The researchers compared the immune response of each of these groups by looking at the levels of antibodies in their blood. They found that up to four years later, women in all of the vaccine groups continued to have antibodies that would protect them from infection with HPV strains 16 and 18 (the two strains covered by Cervarix). Women who received just one dose of the vaccine had lower levels of antibodies than those who received all three, but the levels remained stable, suggesting that there was a lasting response. Women who received two doses six months apart appeared to have just as many antibodies as those who got all three. Also, women who received one dose and those who received two had antibody levels that were between five and 24 times higher than those of women who had never been vaccinated but were infected with HPV. The researchers believed these results suggest all three doses may not be necessary.
If confirmed, these
findings will have the most impact in the developing world, where resources are scarce and cervical cancer rates high. Worldwide, more than 275,000 women die from cervical cancer each year (compared to about 3,900 in the United States). The vaccine costs about $130 per dose; if each woman needs fewer doses to be protected, more women can receive the vaccine for the same overall investment. As Mahboobeh Safaeian, the study’s author, noted to HealthDay, “Vaccination with two or even one vaccine dose could simplify the logistics and reduce the cost of vaccination in the developing world, where more than 85 percent of cervical cancer occurs and it is the most common cause of cancer death in women.”
The results may also have an impact in the United States, where, as RH Reality Check has reported, the HPV vaccine has been something of a tough sell. Despite the fact that an estimated 79 million people in this country are infected with HPV and the virus causes over 20,000 cases of cancer each year (cervical cancer as well as cancers of the head, neck, throat, genitals, and anus), parents seem reluctant to vaccinate their children. In 2012, the Centers for Disease Control and Prevention (CDC) found that only 53.8 percent of girls had initiated the vaccine series by getting the first shot, and even fewer (33.4 percent) had completed all three shots in the series. Moreover, a CDC survey of parents found that many did not intended to take their daughters back to complete the vaccination process. Though, clearly, we have to a better job of explaining the importance of the vaccine as well as the current recommendation that young people receive three doses, if one or two doses are sufficient, perhaps we could increase the percentage of girls who are protected.
A recent study in the United States also supports the theory that women are protected after fewer than three doses of the vaccine. As RH Reality Check reported in June, a study published in the Journal of Infectious Diseases found the proportion of teen girls infected with the strains of HPV that the vaccine addresses has dropped by 56 percent since the vaccine was introduced. The study’s author, Lauri Markowitz, told the Washington Post that the results suggest those teens most in need of the vaccine’s protection were getting it, and that by preventing the virus in them, their peers were protected as well. She added that the fact protection seems to have set in even though so few teens in the United States have received the recommended three doses of the vaccine warranted further study and discussion about whether all three shots are necessary.
The authors of the current study also believe that additional research is necessary, in part because the Costa Rican study involved a relatively small sample of women. Moreover, that study looked at Cervarix, one of the two HPV vaccines available in the United States. The majority (99 percent) of young women who have received the vaccine here, however, have relied on the other brand name version, Gardasil, which appeared on the market first and protects against two additional strains of the virus.
Though this news is promising, until further research confirms it and guidelines change, parents and young women should continue to follow the current recommendations and obtain all three doses of the vaccine.