Countries around the world are seeing substantial drops in human papillomavirus infections that cause cervical and other forms of cancer, a strong sign HPV-vaccination programs are working, according to Canadian research published on Wednesday.
HPV infections, which are sexually transmitted, are linked to cervical, head and neck, penile, vaginal and other forms of cancer, as well as genital warts. The first HPV vaccine was licensed in 2007 and now dozens of countries around the world, including Canada, have adopted vaccination programs to protect young people.
The analysis of 65 studies of HPV-vaccination programs in developed countries shows they are leading to important decreases in HPV infection rates. For instance, there was an 83-per-cent drop in the prevalence of HPV 16 and 18 among girls aged 13 to 19 in the years after vaccination programs were introduced, the researchers found. HPV 16 and 18 are responsible for about 70 per cent of all cervical cancer cases. The studies included about 60 million people in 14 countries.
The findings also show that high-grade cervical lesions, which can lead to cancer, dropped substantially after vaccination programs were adopted. There was a 51-per-cent drop in vaccinated girls aged 15 to 19 and a 31-per-cent drop in those 20 to 24.
In the coming years, researchers expect rates of cervical cancer will also start to decrease substantially, as people who were vaccinated as children get older.
“What our results are showing is strong evidence that HPV vaccination is working to prevent cervical cancer in real-world settings because HPV infections, which are the cause … are significantly declining,” said Marc Brisson, a professor and epidemiologist at Laval University in Quebec City.
Dr. Brisson said the research shows important decreases in other HPV types, such as those linked to genital warts. And the findings show vaccination programs appear to offer good herd protection to boys, who weren’t originally included in many HPV immunization campaigns.
But it’s still important to vaccinate boys to ensure maximum protection, Dr. Brisson said, adding that some groups, such as men who have sex with men, would be vulnerable to cancer-causing HPV infections if they weren’t vaccinated.
“By vaccinating boys in addition to girls, what we are predicting is the declines will occur faster and there will be more impact,” Dr. Brisson said.
The World Health Organization has been pushing for adoption of targets to eliminate cervical cancer between 2020 and 2030. According to the WHO, the vast majority of cervical-cancer deaths worldwide occur in low- and middle-income countries and experts have called for more work to be done to expand vaccination to those areas.
The study was funded by the World Health Organization, a Quebec government research grant and a grant from the Canadian Institutes of Health Research. The authors declared no conflicts of interest.