The human papillomavirus (HPV) vaccination program has achieved a degree of herd immunity less than 20 years after its introduction in Quebec, according to research conducted at Université Laval.
The program is so effective that even unvaccinated young people are benefiting from a form of immunity, according to Dr. Chantal Sauvageau’s team.
“We’ve seen a reduction in the types of HPV most likely to lead to cancer, even in people who haven’t been vaccinated,” explained the professor. “This is what we call herd immunity.”
The human papillomavirus family includes more than a hundred variations.
There are some HPV strains with a low risk of causing cancer and a dozen others with a high risk of causing cancer.
HPV is transmitted mainly by sexual contact and is present in virtually all cases of cervical cancer.
It also causes genital or anal condyloma, as well as lesions that can lead to cancers of the throat, vagina, vulva, anus and penis.
The team, led by Sauvageau, measured HPV prevalence in 369 sexually active, HPV-unvaccinated men aged 16 to 20, recruited between September 2020 and August 2022.
They found that the prevalence of the four HPV strains covered by the first vaccines used in Quebec was 0.5 per cent.
On the other hand, a Quebec study carried out among people aged 18 to 24 prior to the implementation of the vaccination program revealed that HPV type 16 was the most prevalent in this group, and had been detected in 16 per cent of men.
This means, Sauvageau clarified, that HPV circulation has become so low that even unvaccinated people “enjoy a form of protection attributable to herd immunity.”
“These vaccines work at over 95 per cent,” said Sauvageau. “When you can vaccinate before the onset of sexual activity, it gives the results we see here when we have good vaccine coverage.”
In the United States, where vaccination coverage is less widespread, there is a form of herd immunity, but to a lesser extent, added Sauvageau.
“The recent, much-publicized upsurge in measles cases is a good example of what can happen when vaccination coverage declines,” she said.
The HPV vaccination program was first rolled out in Quebec in 2008.
Initially offered to girls aged nine to 17, it was extended to boys in 2016.
Today, the vaccine protects against nine strains of the virus and is offered to young people aged nine to 20.
The findings were published in The Journal of Infectious Diseases.
-- This report by The Canadian Press was first published in French on March 18, 2024.
