Human papillomavirus (HPV) vaccination programs have led to significant decreases in cases of anal and genital warts, HPV infections, and precancerous lesions in young girls and women, providing evidence the vaccines could lead to a significant drop in cervical cancer rates, according to a study published recently in The Lancet.

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A vaccine that can prevent cancer

HPV can lead to cervical, vulvar, vaginal, anal, penile, and throat cancers, as well as genital warts. According to the CDC, about 14 million people become newly infected with HPV each year, and about 33,700 adults are diagnosed with cancer caused by HPV, including 12,000 women with cervical cancer.

In the United States, FDA has approved Merck's Gardasil 9 to protect against nine strains of the HPV virus, though it is not effective against strains to which individuals already have been exposed. FDA also has approved GlaxoSmithKline's Cervarix for use in females ages 9 to 25 to protect against two strains of the virus. According to experts, the vaccines are most effective when administered before people become sexually active.

However, data suggest the vaccines also can benefit older individuals. CDC's Advisory Committee on Immunization Practices last month voted 10 to 4 to recommend HPV vaccines for women and men ages 27 to 45 if they have consulted with their providers and determined they are not adequately vaccinated against HPV, the Washington Post reports.

Study details

For the study, researchers assessed HPV vaccination's effects by analyzing 65 separate studies that were conducted over eight years and published between Feb. 1, 2014, and Oct. 11, 2018. The studies included a total of 66 million female and male patients under age 30 who lived in 14 high-income countries where HPV vaccine programs had been introduced as early as 2007. The researchers examined and compared the shares of young girls, boys, and men in the countries that had been diagnosed with anal and genital warts, HPV, and/or precancerous lesions—which can predict cervical cancer—in pre-vaccination and post-vaccination periods. Post vaccination periods typically spanned between five to eight years after vaccination. The researchers focused on precancerous lesions because it can take years for an HPV infection to develop into cancer.

Findings

Overall, the researchers found the vaccine is highly effective, and could provide unvaccinated girls and boys partial protection from HPV and HPV-related cancers if enough young girls and boys receive the vaccination.

The researchers found "strong evidence" that vaccinations against HPV work "to prevent cervical cancer in real-world settings." Specifically, they found the HPV vaccine led to a 51% decrease in diagnoses of precancerous lesions among teenage girls ages 15 to 19 who were screened, and a 31% decrease among women ages 20 and 24 who were screened.

According to the researchers, the vaccine's protective quality was strongest in countries where more women were vaccinated, the New York Times reports. For example, the researchers found diagnoses of HPV 16 and 18, which are the two strains of HPV responsible for 70% of HPV-related cancers, decreased by 83% among teenage girls and 66% among women ages 20 to 24 in countries where the HPV vaccine had been distributed for longer than five years.

The researchers also found HPV vaccine distribution for longer than five years resulted in diagnoses of anal and genital warts decreasing by:

• 67% among teenage girls;
• 54% among women ages 20 to 24;
• 50% among teenage boys; and
• 31% among women ages 25 to 29.

Though the researchers found strong evidence showing the HPV vaccine is effective, they warned against extrapolating the findings to low-income countries. Specifically, the researchers noted distinctions between Australia, where the vaccine was introduced 12 years ago and is widely accepted, and low-income countries, where there is less data on the vaccine's effectiveness since it was introduced in more recent years.

Comments

David Mesher, a principal scientist at Public Health England who was involved with the study, said, "We're seeing everything that we'd want to see. We're seeing reductions in the key HPV infections that cause most cervical disease, and we're seeing reductions in cervical disease."

Marc Brisson, a biostatistician at Laval University in Quebec and one of the study's authors, said the World Health Organization has noted that eliminating cervical cancer "may be possible in many countries if sufficient vaccination coverage can be achieved." Brisson said the study's findings suggest that countries "should be seeing substantial reductions in cervical cancer in the next 10 years" (Kelland, Reuters, 6/26; McNeil, New York Times, 6/27; Bote, USA Today, 6/27; FDA website, accessed 7/3; Bever, Washington Post, 6/26; Drolet et al., The Lancet, 6/26).