A new study out Wednesday in the BMJ is the latest to showcase even the short-term benefits of the human papillomavirus (HPV) vaccine. It found that the routine vaccination of preteen girls in Scotland, starting in 2008, led to drastically lower rates of cervical disease by the time the girls turned 20. That included conditions known to raise the risk of cervical cancer later on in life.
There are over 100 different types of HPV that regularly infect humans. Most types cause no symptoms at all, while some can cause annoying but harmless warts on our hands, feet, or genitals, depending on where they like to call home.
High-risk HPV types, however, linger in the cells that line the surfaces of our body, triggering changes that can eventually turn them cancerous. These HPV types account for nearly all cases of cervical cancer, as well as a substantial proportion of cancers in the mouth, throat, anus, and penis.
We’ve had a vaccine available for two of the most common high-risk types of HPV since 2006, when it was at first recommended only for teen girls. Over the years, the window of opportunity for getting the vaccine has expanded, as has the number of HPV types it protects against.
The newest version protects against seven high-risk types that account for 90 per cent of cervical cancers (along with two types that cause genital warts). And young boys and men are now also encouraged to get the vaccine, as are women up to age 45.
Despite this increase in recommended age, getting vaccinated while young provides the most benefit, since it’s incredibly easy to contract HPV once a person becomes sexually active. But rates of childhood HPV vaccination in places like the U.S. are still abysmally low.
According to one estimate, only 35 per cent of children are fully vaccinated by age 15 (the current guidelines call for kids to begin their vaccination from age 11 to 12, with only two shots needed if they get both by age 15; otherwise three shots are required).
That low adherence rate not only hampers the protective effects of the vaccine, it also complicates efforts by researchers to study the real-world impact of the vaccine on a population.
In countries like Scotland, though, routine HPV vaccination was quickly adopted and made commonplace, thanks to a nationally funded vaccination program that targeted 12-to-13-year-old girls starting in 2008, along with a later program that targeted older teens.
But there are other factors that make Scotland an ideal country to test the value of widespread HPV vaccination, according to lead author Tim Palmer, a pathologist at the University of Edinburgh.
“Up until June 2016, we started [cervical disease] screening at age 20, so we’re one of the first countries to have immunized women attend for screening,” he told Gizmodo via email. “We are also one of the few countries to be able to link directly the fact that an individual had or had not been vaccinated and her screening outcome many years later.”
Palmer and his team looked at the records of more than 130,000 women in Scotland who received one of these cervical screenings at age 20. They compared women vaccinated for HPV as young girls to slightly older women vaccinated during the catch-up program and to unvaccinated women born in 1988.
Compared to these unvaccinated women, they found, the women vaccinated as young girls were far less likely to have any kind of cervical disease, defined as the growth of abnormal cells in the cervix. Most importantly, the rate of growths classified as a cervical intraepithelial neoplasia (CIN) grade 3 also dropped substantially, by nearly 90 per cent.
That’s crucial because a CIN3 growth puts women at their greatest risk of someday developing cervical cancer. According to Palmer, the 90 per cent reduction they found is the largest drop seen with CIN3 in any population where HPV vaccination is available.
“Thus, we are confident that the reduction in CIN3 will lead to a reduction in cancers,” Palmer said.
The high vaccination rate in Scotland also had indirect effects, they found. The rate of cervical disease in the minority of women who were eligible but did not get vaccinated dropped as well, meaning vaccine coverage was high enough to provide some herd immunity (put simply, the more protected a population is from a disease, the less opportunity the disease has to spread to unprotected people).
As expected, women who were older when vaccinated still had a lower rate of cervical disease than unvaccinated women, but not to the same degree as those who got the vaccine when young.
All in all, Palmer said, the study shows that Scotland’s HPV program has been an unmitigated success, one that will continue to pay off for decades. And Scotland’s early success story should provide plenty more motivation for other countries to drive up their own local vaccination rates.
That said, it’ll still take some time before we can really be sure that cervical cancer rates will similarly plummet, since many women develop it in their mid 30s and 40s. But Palmer says his team is already at work studying screening data that might show the vaccine’s effectiveness at preventing earlier cases of cancer.
The growing success of the HPV vaccine might eventually lead to changes in how we screen women for cervical cancer, Palmer said, since there’ll be fewer total cases of cancer to catch — a welcome problem, obviously.
“Ultimately, when routinely immunized women form the majority of the women eligible for screening, the need for cervical screening programs should be reviewed; they may no longer be justified,” he said. “However, this point will not be reached in Scotland for at least 25 or 30 years. Before that stage, the frequency and number of screening tests will need to be reviewed; there are suggestions that just two or three tests in a screening ‘lifetime’ will be adequate.”
Currently, in the U.S., it’s estimated there are 12,000 new cases of cervical cancer annually.