Certain strains of human papillomavirus (HPV) are closely linked to invasive cervical cancer. Vaccines that protect against these cancer-causing HPV types have been shown to greatly lower the risk of cervical cancer. As a result, the quadrivalent HPV vaccine is now widely used. This vaccine targets HPV types 6, 11, 16, and 18, which together are responsible for about 70% of cervical cancer cases.
The World Health Organization reports that more than 160 countries now include HPV vaccination in their national immunization programs. In Sweden, young girls can get the quadrivalent HPV vaccine for free through a school-based program, which has led to much higher vaccination rates.
To find out how the quadrivalent HPV vaccine affects long-term cervical cancer risk, researchers tracked girls who got the vaccine through Sweden’s school-based program. They recently shared their results in the British Medical Journal. The study followed these participants for almost twenty years to collect detailed health data.
The study included 926,362 girls in Sweden who received the quadrivalent HPV vaccine. About 40% got at least one dose. Over the follow-up period, 930 women developed cervical cancer. Of these, 833 cases occurred in women who were not vaccinated, while only 97 occurred in those who had been vaccinated. The vaccine worked best for girls who got it before age 17. Those vaccinated at age 17 or older remained protected, but the effect was smaller.
The study also highlighted how well the school-based vaccination program worked. Girls born between 1985 and 1988 made up the “opportunistic cohort” because they could only get the vaccine if they found it themselves and paid for it. Girls born after 1999, called the “school-based cohort,” could receive the vaccine through the school program. Women in the school-based cohort had a 72% lower risk of cervical cancer compared to those in the opportunistic cohort.
This research shows that offering the quadrivalent HPV vaccine through school-based programs has clear benefits. The study was large and followed participants for many years. The results offer important information for anyone involved in creating or improving cervical cancer prevention programs.
Sources: J Clin Pathol, Lancet, BMJ
