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18-03-2013 | Legal medicine | Article

Young age maximizes HPV vaccine effectiveness

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medwireNews: Emerging real-world data have shown that human papillomavirus (HPV) vaccination in early adolescence provides the strongest protection against genital warts.

Conversely, results from the Swedish registry study showed that virtually no benefit was conferred to women who received the vaccine after the age of 22 years.

The study included 2,209,263 women and girls aged 10-44 years between 2006 and 2010, of whom 5.6% received at least one dose of the quadrivalent HPV vaccine. Vaccination coverage was highest among teenage girls, at 31.9% in the 18-19 years group and 24.7% in the 13-17 years group.

Vaccine effectiveness against genital warts was 93% among girls who were vaccinated before the age of 14 years. This level of efficacy decreased with age at vaccination with corresponding rates of 80% in the 14-16 years group, 71% in the 17-19 years group, and 48% in the 20-22 years group.

The study also highlighted that parental education status had a significant impact on the likelihood of vaccination. In particular, women and girls whose mother had a university level education were 8.6 times as likely to be vaccinated as those whose mother did not.

The study also provides the first individual-level data on the relationship between HPV vaccination and genital warts incidence. Sweden's healthcare system, which links patient records through multiple registries, made such an approach possible, the authors explain.

They add, however, that their findings are limited by the fact that, at the time of the study, residents had to pay for the vaccine themselves, and therefore coverage preferentially reached those of higher socioeconomic status.

"Now that the vaccination is free and offered through the schools, it will be more evenly distributed in the population," said author Lisen Arnheim-Dahlström (Karolinska Institute, Stockholm, Sweden) in a press release.

In an accompanying editorial, Jennifer Smith (University of North Carolina, Chapel Hill, USA) and Elisabete Weiderpass (Karolinska Institute, Stockholm, Sweden) say that the study was possible due to this uneven coverage before low genital warts incidence and herd immunity would render it impossible.

They add that recent study results suggest that one- and two-, as opposed to the standard three-dose vaccination schedule may be effective, but the authors did not include this information in their analyses.

Nevertheless, they say the data presented indicate that "in countries struggling to bear costs of the HPV vaccination, targeting girls aged less than 14 years may be more cost effective than investing in catch-up programs for relatively older women, in particular those aged greater than 20 years."

By Kirsty Oswald, medwireNews Reporter

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