“The magnitude of the effect is greater than expected,” study author Dr. Tim Palmer from the University of Edinburgh told.
Receiving three doses of the vaccine at the recommended ages of 12 to 13 was associated with “a profound reduction of cervical disease seven years later,” he and his colleagues report in The BMJ.
One of the most common sexually transmitted diseases, HPV doesn’t cause symptoms and usually goes away on its own. But the virus can cause cancer of the cervix, the fourth most common cancer in women, as well as cancers of the throat and penis.
Palmer’s team studied 138,692 women, about half of whom had been fully vaccinated against HPV either at ages 12-13, or later in their teens. At age 20, the women all had tests to look for abnormal cells on the cervix – called cervical intraepithelial neoplasia, or CIN – that can lead to cancer.
Rates of CIN were low overall. But compared with unvaccinated women, vaccinated women had an 89 percent lower rate of CIN grade 3 or worse (0.59 percent in unvaccinated women versus 0.06 percent in the vaccinated group), an 88 percent lower rate of CIN grade 2 or worse (1.44 percent versus 0.17 percent), and a 79 percent lower rate of CIN grade 1 (0.69 percent versus 0.15 percent).
Grades 2 and 3 are usually treated with surgery.
Girls who were vaccinated at ages 12-13 got a greater benefit: the vaccine was 86 percent effective for them, and 51 percent effective when given at age 17.
“The findings are dramatic and document a considerable reduction in high-grade cervical disease over time,” Julia Brotherton, medical director at VCS Foundation in East Melbourne, Australia, writes in an editorial published with the study.
In the U.S., many girls and boys don’t receive the vaccine at least in part because their parents may question whether it’s necessary to protect them against a sexually transmitted disease at an age when they think children shouldn’t be having sex, previous studies have found.
Scotland, which has an organized national cervical screening program, introduced a national immunization program against HPV in 2008, targeting girls aged 12 and 13, followed by a three-year catch-up program up to age 18.
The study also revealed a decreasing rate of disease in unvaccinated women. “This is called herd protection and is a function of the high uptake of vaccine in Scotland,” Palmer explained. Unvaccinated women are being protected because the spread of HPV between men and women has been interrupted because there are not enough susceptible women, he said.
There were an estimated 570,000 new cervical cancer cases globally in 2018, representing 6.6 percent of all female cancers, according to the World Health Organization, with about 90 percent of deaths from cervical cancer occurring in low- and middle-income countries.
These countries, however, do not have the resources to support organized screening, the authors write, highlighting the importance of developing vaccines against the most important cancer-causing HPV strains.
In February, the WHO and cancer experts called the HPV vaccine a “critical” health tool and said access to it should be scaled up as swiftly as possible, especially in poorer countries.