The HPV vaccine is far more effective than expected, with benefits extending beyond those who receive the vaccine, a study published Wednesday finds.
The new study, published in The Lancet, suggests that the more people who receive the vaccine, the better. That’s because vaccination not only reduces rates of HPV infection and the presence of precancerous cells in the cervix in people who receive the vaccine, it also reduces rates of HPV-related diseases in people who were not vaccinated.
The findings come as a U.S. federal advisory panel recommended Wednesday that the HPV vaccine be given to both men and women up to age 26.
HPV, or human papillomavirus, is the leading cause of cervical cancer. The virus can also cause other cancers, including cancers of the penis, head and neck, as well as conditions like genital warts.
The HPV vaccine was first introduced in 2006. Since then, more than 115 countries and territories have implemented it in their vaccination programs. The World Health Organization recommends that girls ages 9 to 13 receive two doses of the vaccine.
“The impact of the HPV vaccination has actually exceeded expectations,” said Lauri Markowitz, associate director of science for HPV at the Centers for Disease Control and Prevention, who worked on the study. "The trials showed that HPV vaccines are very effective, and data from the real world has confirmed that.”
Indeed, the reductions in HPV infections and precancerous cells “are a first sign that vaccination could eventually lead to the elimination of cervical cancer as a public health problem,” the study's lead author, Mélanie Drolet, an epidemiologist at Laval University in Canada, said in a statement.
The Lancet study expanded upon a 2015 meta-analysis that had looked at the real-world effects of the vaccine. The new analysis was updated to include a total of 65 studies, which spanned eight years and included more than 60 million people living in 14 countries. Each study measured either changes in the number of new HPV infections, genital warts diagnoses or cases of abnormal cells associated with cervical cancer in countries before and after they adopted routine HPV vaccination in girls. (Two countries included in the analysis, the U.S. and Australia, also recommend the vaccine for boys.)
The researchers found that, in these countries, there was a significant decrease in the prevalence of two strains of HPV that cause 70% of cervical cancers, HPV 16 and 18. (There are more than 100 strains of HPV, 14 of which are known to cause cancer. The HPV vaccine protects against up to nine strains.) In addition, there was a decrease in the prevalence of precancerous cells in the cervix, which can develop into cancer.
What’s more, in countries where at least half the population that was targeted for vaccination had actually received the vaccine, researchers saw evidence of herd immunity, meaning there was a decrease in the prevalence of HPV-related diseases even among those who weren’t vaccinated. This is because vaccination leads to fewer HPV hosts.
These countries also saw a decrease in genital warts diagnoses among unvaccinated boys and older women. And among girls within the age groups targeted for vaccination, there were fewer diagnoses of three HPV strains that the vaccine does not specifically protect against, a phenomenon called cross-protection. Countries in which people in multiple age groups received the vaccine also saw a greater decrease in HPV-related disease.
"This paper shows that with a broader age range that’s targeted, you’ll find greater impact in your vaccination program,” Markowitz told NBC News.
Lagging vaccination rates
Despite the widespread benefits of the vaccine, however, HPV vaccination rates in the U.S. are still lagging behind those of other adolescent immunizations. The U.S. was the first country to implement HPV vaccination for both genders, but the CDC has found that many parents and health care providers don’t yet see a need to vaccinate boys. Parents have also expressed concerns about the vaccine and its costs, the CDC found.
According to Debbie Saslow, managing director of HPV and gynecological cancers at the American Cancer Society, the lagging rates are not entirely because parents are against vaccinating their kids; rather, the way some doctors are presenting the vaccine also plays a role.
Two required vaccinations, for tetanus and meningitis, are administered at the same time as HPV, around age 12. Saslow said HPV is usually presented as an optional third vaccine at that time, and one that patients can delay another year.
“Providers often think they’re recommending all three vaccines, but they’re actually making the third, the HPV vaccine, optional,” Saslow told NBC News. “They’re just suggesting it or doctors are setting it apart from the other two in some way.”
The fact that HPV is a sexually transmitted infection could also be a hard concept for parents to come to terms with. Saslow said beliefs about sex may be a factor that deters parents from opting to have their children vaccinated against HPV.
“Despite all that, vaccination rates are continuing to grow,” she said.
Indeed, the number of adolescents in the U.S. who received at least one dose of the HPV vaccine has increased by 5% each year since 2013. The CDC recommends everyone receive the first dose by age 12. Though adults up to age 45 can still be vaccinated, the vaccine may be less effective. And while the WHO does recommend that girls 9 to 13 get vaccinated against HPV, it does not yet recommend that all genders receive the vaccination. That could change in response to study results that continue to show the vaccine has substantial impact on public health.
That impact on public health is cancer prevention. Ultimately, that’s the “main goal of the HPV vaccination program," Markowitz said. "We’re seeing an impact on one of the HPV outcomes that is close to a cancer outcome.” (Because cervical cancer can take decades to develop, it’s not yet possible to study the effects of the vaccine on cervical cancer rates, Drolet noted in the statement.)
In particular, the study found the HPV vaccine led to a reduction in the rates of abnormal pap smear findings. Pap smears are used to detect abnormal cells in the cervix that can sometimes develop into cancer. Five to nine years after a population was vaccinated against HPV, the researchers found a more than 50% reduction in cases of these pre-cancerous cells in girls 15 to 19. In vaccinated women 20 to 24, there were one-third fewer cases of these cells.
A separate study, published in April in The BMJ, found a 90% reduction in cases of pre-cancerous cells in young women in Scotland within the first decade of introducing the HPV vaccine.
But vaccination is only one piece of cervical cancer prevention; screening is also necessary.
Whether or not a person has received the HPV vaccine, getting cervical cells regularly tested — through pap tests and HPV screening — is still a crucial to reducing cases of cervical cancer and early detection, said Diane Harper, senior associate director of the Michigan Institute for Clinical and Health Research. Rates of invasive cervical cancer dropped significantly in the U.S. when cancer screening was introduced in the 1940s, and there were less than half the number of cases in 2007 that there were in 1973, largely due to screening.
“Vaccination and screening together make a program,” Harper told NBC News. “Very few HPV cases progress into cancer, but the only way we’re going to find those that do is through the screening program.”