(RxWiki News) Not only does the HPV vaccine protect against human papillomavirus, but it also reduces the risk of cancers caused by HPV. Yet it only protects a person if it lasts long enough.
A recent study found that the immunity provided by the HPV vaccine lasted at least eight years.
HPV, or human papillomavirus, is a viral infection that is usually transmitted sexually, though it can also be transmitted through non-sexual contact with the sex organs, such as during a baby's birth.
Some strains of HPV can cause cervical cancer in women, penile or anal cancer in men, or mouth and throat cancer in anyone.
"Follow the CDC recommended immunization schedule."
The study, led by Daron Ferris, MD, of the Department of Obstetrics and Gynecology at Georgia Regents University in Augusta, looked at the long-term effectiveness of the HPV vaccine.
The vaccine tested was called "quadrivalent" because it protects against four strains of the virus: HPV 6, 11, 16 and 18.
The researchers followed 1,661 children and teens, aged 9 to 15, for eight years.
Two thirds of these participants received the first dose of the four-strain HPV vaccine at the start of the study. Then they received additional doses two and six months later.
The other third of participants received a placebo (fake) vaccine at the start and at two and six months into the study.
Then, two and a half years into the study, the participants who had gotten the placebo shot were given the three doses of the real vaccine.
To find out the effectiveness of the vaccine, the researchers drew blood from the participants to see if their bodies had antibodies against HPV.
Antibodies are the immune system cells that fight an infection. They are created against a specific disease when a person receives a vaccine for that disease.
The blood samples showed that all the participants — those who got the HPV vaccine from the start and those who got it later on in the study — still had antibodies to protect against the four strains of the virus.
This finding meant that the vaccine was still effective. There also was no evidence that the antibodies would not continue to remain there for future years.
However, no vaccine is 100 percent effective. Among those vaccinated at the start of the study, four participants developed an HPV-related infection that went away within a year.
Then, among those who were vaccinated several years into the study, seven participants experienced an HPV-related infection and one had an HPV-related disease.
That means the vaccine could not protect every single person completely. However, the rate of infections should have been much higher if there had been no vaccinations.
Of all the participants, only one person experienced a serious side effect. That person developed Ball's palsy, a muscular weakness in the facial nerve, for two weeks before it went away with steroid treatment.
No other serious side effects occurred.
"These long-term follow-up data, along with other extensive safety data, should help to encourage practitioners and reinforce national recommendations for HPV vaccination of all preadolescents and young adolescents," the authors wrote.
The study was published Aug. 18 in the journal Pediatrics. The research was funded by Merck & Co., which manufactures the HPV vaccine.
Five authors have received grant funding, speaker fees, consulting fees or advisory board appointments from Merck and/or GlaxoSmithKline, which manufactures a different HPV vaccine. Four of the authors are Merck employees who also hold stock or stock options in the company.