An Australian study has found that seven years after the implementation of the schools-based HPV vaccination program there has been a small but significant reduction in HPV among unvaccinated women, suggesting a herd immunity effect.

Additionally among vaccinated women there has been a surprising decrease in HPV genotypes not contained in the vaccine, revealing an unexpected cross-protective effect.

Medical Director of the National HPV Vaccination Program Register, Dr Julia Brotherton said that it is the first time, outside clinical trials, that evidence of a cross-protection effect from the quadrivalent vaccine has been observed. “We noted significant vaccine effectiveness against HPV 31, 33 and 45 in fully vaccinated women, compared with unvaccinated women, which suggests the vaccine may provide some protection beyond the target HPV types” she said.

The study compared the prevalence of HPV types in 1058 women aged 18-24 and recruited in 2010-2013 after the vaccination program began with 202 women of the same age who were recruited before it was introduced in 2007.

There was a 77% decline in the prevalence of HPV 6, 11, 16 and 18 in the post-vaccinated period, with a 92% decline in vaccinated and a 35% decline in those who were not vaccinated.

“The fact that we could see a reduction in women who had received no doses of the vaccine suggests that everyone is deriving protection simply because women aren’t infecting males who are then not infecting unvaccinated women. It certainly is an obstruction of transmission from vaccinated women creating a heard effect” she said.

Dr Brotherton also noted that the benefits of the vaccine may extend beyond the pre-adolescent age group. “While you get maximum benefit if you have the vaccine before you’re ever exposed to the virus, there is now evidence that for women who have already been treated for a high-grade lesion, if they then receive the vaccine, their risk of recurrence is reduced”.

“It won’t cure any infection you already have but what it can do is prevent new infections. It’s certainly a conversation some women might like to have with their GP” she said.