Herd Immunity leads to falling HPV prevalence in unvaccinated men

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Amidst the raging controversy in the United States regarding vaccines, the HPV vaccine has received quite a bit of attention. Some public health officials (and pharmaceutical companies) would like the vaccine to be mandatory, but since the recommended age is pre-teen, some parents fear this sends a bad message about sexual activity in an already over-sexualized culture.

Both sides make flawed arguments. The bottom line is the vaccine prevents cancer.

Human papillomavirus is definitely troublesome. It causes 99% of cervical cancers in women, and it is also behind an increase in head and neck cancers, mostly in younger white people (i.e., those in their 40s and 50s). While this is certainly a public health concern, HPV poses nothing like the risk that measles, diphtheria, or whooping cough do. And the vast majority of people who become infected with HPV, even the high-risk strains, do not go on to develop cancer.

Human Papilloma Virus - a sexually transmitted virus that causes genital warts or even cancer. Image Courtesy : Wikimedia Commons
Human Papilloma Virus – a sexually transmitted virus that causes genital warts or even cancer. Image Courtesy : Wikimedia Commons

Nevertheless, new statistics coming up from Australia gives us the supporters reasons to rejoice.

Men who are unvaccinated for HPV are receiving protective benefits from the women who are vaccinated. In other words, this is a prime example of herd immunity in action.

Australia’s HPV Vaccination Program

Australia initiated its free HPV vaccination program in 2007. At the beginning only females aged 12 -26 were vaccinated and later in 2013, boys were included as well. The vaccine was targeted against HPV-16 and HPV-18, both “high-risk” strains that cause cancer, as well as HPV-6 and HPV-11 which cause genital warts.

Dorothy Machalek and her group wanted to determine if those who remained unvaccinated were receiving indirect protection. Penile swab samples were collected and analyzed for HPV DNA.

HPV

The team found that the prevalence of the 4 HPV genotypes among 511 unvaccinated male subjects was significantly lower in those aged ≤25 than in those aged >25 years: 3.1% versus 13.7%, respectively. By contrast, the prevalence of high-risk HPV genotypes other than 16 and 18 remained the same across age groups: 16.8% in men aged ≤25 years and 17.9% in those aged >25 years.

Thereby, they concluded that there was a 78% lower prevalence of 4 HPV genotypes observed among younger male subjects.

These data suggest that unvaccinated men may have benefited from herd protection as much as women from a female-only HPV vaccination program with high coverage.

One of the reasons for low prevalence could be the lack of or fewer sexual encounters in younger men than the older ones. However, this data also indicates that they were still being exposed to HPV since the prevalence of HPV strains not targeted by the vaccine was roughly the same in both the younger and older men. That provides substantial validation to the fact this is due to herd immunity.

These encouraging results come close on the heels of reports that unvaccinated children could be banned from attending preschool across Australia. Hopefully, Australia’s success will influence other countries to implement a similar program.