Single Dose of HPV Vaccine May Be Enough to Guard Against Cervical Cancer
Researchers found women who only got 1 of 3 recommended Cervarix doses still showed immune response 4 years later
The doctors then compared those results to data from 113 women who were not vaccinated but had antibodies against the viruses in their blood because they had been infected with HPV in the past.
Up to four years later, all of the women in all three vaccination groups had antibodies for HPV 16 and 18, the two strains Cervarix guards against.
Although antibody levels among women who received one dose were lower than among those who received three doses, the levels appeared stable, according to the researchers, which suggests that these are lasting responses.
Moreover, the levels of antibodies in women from the one- and two-dose groups were between five and 24 times higher than the levels of antibodies in women who were not vaccinated but were infected with HPV.
The contents of the HPV vaccine might provide another explanation, Safaeian said.
The vaccine is created using genetically engineered versions of the virus that prompt an immune response but do not have the ability to multiply and cause illness, she explained.
This type of vaccine might cause a stronger immune response than vaccines made from parts of live viruses (such as the tetanus vaccine) which often require periodic boosting to maintain immunity, Safaeian said.
Debbie Saslow, director of breast and gynecologic cancer for the American Cancer Society, called the findings "very exciting."
"This would be absolutely amazing if we could only give one dose," she said.
However, Saslow noted a few concerns. For one thing, the study did not involve the HPV vaccine used 99 percent of the time in the United States -- Gardasil, which guards against four strains of the virus, she noted.
Also, researchers could only verify protection for four years after receiving the dose. "If we are vaccinating girls at age 12, we need to make sure that immunity lasts," Saslow said. "We don't know, and they don't know, if having three doses will last any longer than one dose."
Finally, she pointed out that a very small number of women were involved in the Costa Rican study, and recommended that these results be verified by tracking girls in the United States who are receiving the vaccine.
"We need to set up some sort of surveillance system for those who only got one or two doses," Saslow said. "If we're identifying those girls, let's see if we can follow them. We don't need to start a big randomized trial. We can look back using medical records."