HPV Vaccine Maintains 79% Cervical Cancer Protection 13-15 Years After Vaccination in Swedish Study

HPV vaccination before age 17 reduces invasive cervical cancer risk by 79 percent - and that protection shows no sign of weakening over 18 years of follow-up. Those are the central findings of a nationwide Swedish study published in The BMJ, covering 926,362 women born between 1985 and 2001 and followed from 2006 through 2023.

The study is among the largest and longest follow-up analyses of HPV vaccine effectiveness published to date. It used national registers to compare cancer incidence in vaccinated and unvaccinated women, and it specifically examined whether protective effects decline with time - the question most pressing for countries deciding whether booster doses are necessary or whether current vaccination schedules are sufficient for long-term protection.

How protection holds over time

For women vaccinated before age 17, the analysis showed 79 percent lower cervical cancer risk compared to unvaccinated women. At 13 to 15 years after vaccination, the risk reduction remained at 77 percent - statistically indistinguishable from the overall effect, with no evidence of a declining trend.

Women vaccinated at age 17 or older showed a lower overall risk reduction: 37 percent compared to unvaccinated women. But within this group, protection appeared to improve with time since vaccination - a 46 percent lower risk at 10 to 12 years, rising to a 77 percent lower risk at 13 to 15 years. This pattern may reflect the longer latency between infection and cervical cancer, meaning later-vaccinated women who were potentially already exposed before vaccination begin showing the benefit of preventing new infections as enough time passes.

During the study period, 930 cases of invasive cervical cancer were identified. Of these, 97 occurred in vaccinated women and 833 in unvaccinated women - a ratio that understates the vaccine effect because vaccinated women were younger and had shorter follow-up than the unvaccinated group.

Population-level decline already visible

The data show a generational decline in cervical cancer rates that tracks the rollout of HPV vaccination in Sweden. Women born between 1985 and 1988 - before vaccination was available - reached a rate of approximately 250 cases per 100,000 by age 38. Women born between 1999 and 2001, who came of age during the vaccination program, showed a rate of only 4 per 100,000 by age 24. The absolute numbers are still small in the youngest cohort - they have not yet reached the ages of highest cancer incidence - but the direction is unambiguous.

Limitations

The study is observational, relying on national registers rather than randomized assignment. Some vaccinated women may have been misclassified as unvaccinated if their vaccination records were incomplete. Healthy volunteer bias - the possibility that people who chose vaccination also had healthier behaviors overall - cannot be fully excluded. Smoking and sexual behavior history, which affect cervical cancer risk independently of vaccination, were not directly measured. The researchers note that results were consistent across multiple sensitivity analyses, which reduces but does not eliminate concern about these limitations.

The study vaccine is the quadrivalent type, targeting HPV strains 6, 11, 16, and 18. The newer nonavalent vaccine, which targets additional strains, was not evaluated in this cohort. The authors conclude that their findings support global strategies for cervical cancer elimination through high-coverage routine vaccination programs, particularly when delivered before age 17.