Quadrivalent human papillomavirus (HPV) vaccination was associated with a substantial reduction in the incidence of cervical cancer in a Swedish review of more than 1 million girls and women vaccinated from 2006–2017.
It’s been shown that the vaccine (Gardasil) helps prevent genital warts and high-grade cervical lesions, but until now, data on the ability of the vaccine to prevent cervical cancer, although widely assumed, had been lacking.
“Our results extend [the] knowledge base by showing that quadrivalent HPV vaccination is also associated with a substantially reduced risk of invasive cervical cancer, which is the ultimate intent of HPV vaccination program,” said investigators led by Jiayao Lei, PhD, a researcher in the Department of Medical Epidemiology and Biostatistics at the Karolinska Institute, Stockholm, Sweden.
The study was published online October 1 in The New England Journal of Medicine.
“This work provides evidence of actual cancer prevention,” commented Diane Harper, MD, an HPV expert and professor in the Departments of Family Medicine and Obstetrics & Gynecology at the University of Michigan, Ann Arbor, Michigan. She was the principal investigator on the original Gardasil trial.
This study “shows that the quadrivalent HPV vaccine provides prevention from the sexually transmitted HPV infection that actually reduces the incidence of cervical cancer in young women up to 30 years of age,” she said when approached for comment.
However, she also added a note of caution. These new results show “that vaccinated women still develop cervical cancer, but at a slower rate. This makes the connection between early-age vaccination and continued adult life screening incredibly important,” Harper told Medscape Medical News
Cervical cancer was diagnosed in 19 of the 527,871 women (0.004%) who had received at least one dose of the vaccine, vs 538 among the 1,145,112 women (0.05%) who had not.
The cumulative incidence was 47 cases per 100,000 vaccinated women and 94 cases per 100,000 unvaccinated women. The cervical cancer incidence rate ratio for the comparison of vaccinated vs unvaccinated women was 0.37 (95% CI, 0.21 – 0.57).
The risk reduction was even greater among women who had been vaccinated before the age of 17, with a cumulative incidence of four vs 54 cases per 100,000 for women vaccinated after age 17. The incidence rate ratio was 0.12 (95% CI, 0.00 – 0.34) for women who had been vaccinated before age 17, vs 0.47 (95% CI, 0.27 – 0.75) among those vaccinated from age of 17 to 30 years.
Overall, “the risk of cervical cancer among participants who had initiated vaccination before the age of 17 years was 88% lower than among those who had never been vaccinated,” the investigators noted.
These results “support the recommendation to administer quadrivalent HPV vaccine before exposure to HPV infection to achieve the most substantial benefit,” the investigators said.
Details of the Swedish Review
For their review, Lei and colleagues used several Swedish demographic and health registries to connect vaccination status to incident cervical cancers, using the personal identification numbers Sweden issues to residents.
Participants were followed starting