The human papillomavirus (HPV) vaccine reduced cervical cancer cases by 87% among women in the U.K. who received the vaccine when they were 12 or 13 years old, according to a new study.
These new findings are based on follow-up data from a vaccination program that began in the U.K. in 2008. The strains of human papillomavirus that are transmitted through sexual contact are extremely common around the world, and most people are infected at some point in their lives, typically soon after becoming sexually active, according to The World Health Organization (WHO).
Many HPV infections clear up on their own without causing issues, but some infections can lead to cervical cancer. In fact, nearly all cervical cancer cases around the world are due to an infection with HPV, according to the WHO. Now, more than 100 countries, including the U.K. and the U.S., offer HPV vaccinations to young girls, and some countries are also offering them to young boys to prevent genital warts and cancer.
Related: How do vaccines work?
As part of the U.K. program, girls between the ages of 12 and 13 were given an HPV vaccine called Cervavix, which protects against the two most common types of HPV that account for 70 to 80% of all cervical cancers, according to a statement. The vaccine was also offered to women up to age 18 as a"catch-up" vaccination.
In the new study, the researchers analyzed data collected between 2006 and 2019 from a cancer registry. They compared cervical cancer rates between women who were vaccinated with Cervavix when they were younger and those who weren't; the researchers further divided those who were vaccinated into groups based on their age of vaccination.
Between 2006 and 2019, there were 28,000 cervical cancer diagnoses in the U.K. and 300,000 cases of non-invasive cervical carcinoma (CINN3), abnormal cells on the cervix that can turn into cancer if left untreated. That's about 450 cases of cervical cancer and 17,200 fewer cases of cervical pre-cancer than expected in the general population, according to the statement.
The researchers found that the vaccine was most effective when given to the younger cohort; women who were vaccinated with Cervavix between the ages of 12 and 13 had 87% fewer cases of cervical cancer compared with those who weren't vaccinated. Women vaccinated between the ages of 14 and 16 and those between the ages of 16 and 18, there was a 62% and a 34% reduction in cases compared to the unvaccinated population, respectively. (The vaccine was less effective for girls vaccinated at older ages because more of them were sexually active and therefore exposed to the virus before getting vaccinated. The vaccines work best before people are exposed to the virus.)
"Although previous studies have shown the usefulness of HPV vaccination in preventing HPV infection in England, direct evidence on cervical cancer prevention was limited," senior author Peter Sasieni, a professor in the King’s College London said in the statement. Early modeling had predicted that HPV vaccination would reduce cervical cancer rates substantially in young women, he said.
"The observed impact is even greater than the models predicted," he added.
There are some limitations to the study, including that the vaccinated population is still young and so it's still early to understand the full impact of the HPV vaccination program, according to the statement.
Since 2012, the U.K. has been using another HPV vaccine called Gardasil that protects against four different types of HPV and wasn't evaluated in this paper. The U.S. is administering Gardasil-9, which protects against nine different HPV types. All three vaccines protect against the the two most common HPV types that cause cancer.
The Centers for Disease Control and Prevention (CDC) recommends that two doses of the HPV vaccine be given 6 to 12 months apart to children between the ages of 11 and 12, but can be given as early as age 9. Those who are 15 years of age or older need three doses over 6 months.
Originally published on Live Science.
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Yasemin is a staff writer at Live Science, covering health, neuroscience and biology. Her work has appeared in Scientific American, Science and the San Jose Mercury News. She has a bachelor's degree in biomedical engineering from the University of Connecticut and a graduate certificate in science communication from the University of California, Santa Cruz.