Study data from long-term observation did not indicate any loss of antiviral protection after vaccination against HPV types 16 and 18, but stronger evidence is required to confirm its efficacy.
Researchers from the Robert Koch Institute in Berlin and colleagues performed a systematic literature review and meta-analysis of 15 studies on the efficacy of HPV vaccination. Studies eligible for review had a female population aged 9 to 26 years who were initially negative for HPV-16 or HPV-18. Participants in intervention arms were assigned HPV vaccinations, with outcomes including infection, persistent infections lasting at least 6 months or varying levels of cervical intraepithelial neoplasia (CIN).
Of the identified studies, 10 were randomized controlled trials and five were observational studies. Two trials had a duration longer than 5 years and were considered long term, with all other studies being short term.
Within short-term randomized controlled trials, infections were prevented with 83% efficacy (95% CI, 70-90), with a median follow-up duration of 25.5 months. Persistent infection prevention was estimated at 90% (95% CI, 79-95), with a median follow-up duration of 27 months. CIN grade 2 or worse lesions (CIN2+) were prevented with 84% efficacy (95% CI, 50-95) after 36 months, whereas CIN3+ protection was 94% (95% CI, 83-98) after median follow-up of 36 months.
Only one long-term randomized controlled trial recorded incident infections, observing 94% efficacy (95% CI, 80-98) after 7 years. Persistent infections were prevented with a pooled efficacy of 95% (95% CI, 84-99) during a median 6 years. Again, results concerning CIN2+ came from a single study reporting 86% efficacy (95% CI, –166 to 99) after 7 years, whereas no long-term data were collected for CIN3+.
The five observational studies did not produce estimates of vaccine efficacy.
Evidence quality within short-term studies was considered strong by researchers, except for data on CIN2+, which was considered moderate. Due to wide confidence intervals and the high risk of bias in one of the two long-term studies, long-term data concerning efficacy were evaluated as weak.
“This systematic review shows that there is no evidence from long-term follow-up that vaccine protection following vaccination for HPV types 16 and 18 decreases,” the researchers wrote. “Because only a few randomized controlled trials were conducted for 5 years or longer and these had considerably fewer participants than studies with shorter follow-up, the quality of evidence for long-term protection is lower than that for short-term protection.”
Disclosure: One researcher has received fees for conducting commissioned clinical studies from GlaxoSmithKline and Sanofi, as well as collecting expense reimbursement from GlaxoSmithKline. Another researcher has received recompense from vaccine manufacturers AstraZeneca and Sanofi for education lectures unrelated to any specific product.