MONDAY, Feb. 3, 2020 (HealthDay News) — Methodological problems and study limitations for trials of the human papillomavirus (HPV) vaccine create uncertainty about its ability to prevent cervical cancer in the long term, according to a review published online Jan. 21 in the Journal of the Royal Society of Medicine.

Claire P. Rees, M.B.B.S., from the Queen Mary University of London, and colleagues reviewed 12 published phase 2 and 3 randomized controlled trials to evaluate study design and the ability to determine the efficacy of the HPV vaccine.

The researchers observed the following methodological problems and study limitations in trials: (1) Trials were not designed to detect cervical cancer prevention; (2) data do not extend beyond nine years following vaccination, yet cervical cancer may take decades to develop; (3) efficacy may be overstated as testing was too frequent (six to 12 months versus the standard 36-month interval) and cervical intraepithelial neoplasia (CIN) grades and cancer risk were not considered appropriately (some lesions, as in CIN1, resolve on their own without treatment but were included in composite surrogate outcomes); and (4) trial populations did not match target vaccination populations (e.g., women in trials were older).

“We have good evidence that cervical screening significantly reduces the risk of cervical cancer in women regardless of whether they have been vaccinated,” a coauthor said in a statement.

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