HPV: Vaccines protect even unvaccinated women

Human papillomavirus (HPV) vaccines are truly lifesaving. But their effectiveness extends beyond the individual. They could also offer indirect protection at the population level, thus protecting even unvaccinated women from infection with the virus, the main cause of cervical cancer.

A large, long-term study conducted by a research team at the Albert Einstein College of Medicine in New York City has confirmed this today, demonstrating how HPV vaccinations could provide so-called herd immunity. The details are published in the journal JAMA Pediatrics .

What is HPV?

Human papillomavirus (HPV) is the most common sexually transmitted infection in the world and the leading cause of cervical cancer (but is also linked to the onset of other cancers in the genital area and oropharynx). In our country, according to data published in the report "Cancer in Italy 2024: Numbers," approximately 2,400 new cases of cervical cancer are recorded each year, accounting for approximately 1.3% of all cancers diagnosed in women. Effective vaccines exist against HPV, recommended for boys and girls before the onset of sexual activity. In this new study, the authors were interested in investigating the effectiveness of vaccines in real-world settings, which are less controlled than those used in clinical trials and at high risk (either due to the number of sexual partners or previous sexually transmitted infections), as explained by Jessica Kahn , research leader.

The effectiveness of HPV vaccines

In total, the researchers analyzed over 2,300 adolescent and young adult women between 2006 and 2023. Over these 17 years, HPV vaccination rates increased from 0%—when there was no vaccine—to 82% (vaccines that protect against various HPV serotypes have long been available on the market). With increased vaccination coverage, human papillomavirus infection rates decreased dramatically among vaccinated participants (including women who received only a single dose).

Here are some examples, as summarized in a note from the Albert Einstein College of Medicine: infections from HPV serotypes 16 and 18, which cause over 70% of cervical cancers and are covered by the bivalent vaccine, decreased by 98.4%, while infections from HPV 16, 18, 6, and 11 (covered by the quadrivalent vaccine) decreased by 94.2%. Finally, infections from other serotypes covered by the nonavalent vaccine decreased by 75.7%. And this, the experts point out, occurred without any change in the habits of the women studied.

Cervical cancer removal

The study also found strong evidence of herd immunity, with reductions in infections among unvaccinated women of up to 75% (for infections covered by the bivalent and quadrivalent vaccines). "Our findings," the paper states, "provide new evidence of robust efficacy and herd protection in sexually experienced adolescent girls and young women at relatively high risk for HPV and related cancers, even if they have not received the recommended 2- or 3-dose vaccine series."

These very data, however, are at odds with the poor implementation of vaccination and screening programs globally, as Kahn noted. In some countries, vaccination rates are only a few percentage points. "By expanding the availability of this highly safe and effective vaccine and ensuring access to screening and treatment programs," he concluded, "we can achieve one of the greatest public health victories of our time: the elimination of cervical cancer worldwide."