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CHICAGO -- Vaccination against human papillomavirus (HPV) appeared to be highly effective in preventing the oral infections that can lead to oropharyngeal cancer, a researcher said.

Among young people who had received at least one shot of the quadrivalent vaccine in the years 2011 through 2014, the prevalence of infection by one of the four vaccine strains was 88% lower than it was among those who were unvaccinated, according to Maura Gillison, MD, PhD, of the MD Anderson Cancer Center in Houston. The study was conducted while Gillison was at the Ohio State University Comprehensive Cancer Center in Columbus.

The finding suggests the vaccine has "a tremendous potential to prevent oral infections," Gillison said during a webcast media briefing in advance of the American Society of Clinical Oncology (ASCO) annual meeting.

But she told reporters that so far the population impact of the vaccine has been small, mainly because of low use of the vaccine during the years of the study. From 2011 through 2014, her group estimated that there were some 927,401 vaccine-preventable oral HPV infections -- but just 17% of those, some 169,650 cases, were actually averted.

But there is cause for "considerable optimism," she said, because recent reports suggest uptake of HPV vaccines among girls and boys under 18 is increasing, to about 60% and 40%, respectively, compared with just 25% and 7% in the study population.

The vaccines are indicated to prevent cervical and anal infections, but not oral infections, at least partly because no large studies have suggested the drug is effective, Gillison said.

The findings are "encouraging," commented ASCO President-Elect Bruce Johnson, MD, of Dana-Farber Cancer Institute in Boston, who was one of the co-moderators of the ASCO briefing.

"One of the first steps in preventing cancer is to first prevent the infection," he said. The study shows "you can indeed prevent infection."

Gillison's group conducted a cross-sectional study among 2,627 men and women, ages 18-33 years, who participated in the for 2011 through 2014.

They looked at the prevalence of oral infection with the HPV vaccine serotypes -- 16, 18, 6 and 11 -- among participants who reported they had received at least dose of the drug, compared with those who said they had not.

All participants gave an oral rinse that Gillison's group evaluated for the presence of HPV.

They found that 18.3% reported receipt of at least one shot, including 29.2% of women and 6.9% % of men.

Overall, 0.11% of those who reported vaccination had one of the vaccine strains, compared with 1.6% of those who did not, a difference that was statistically significant.

Among men, who have the greatest burden of oral HPV infection, the respective rates were 0.0% and 2.1%, also a significant difference.

Gillison cautioned that the study was not a prospective randomized clinical trial and can say nothing about cause and effect. But the findings suggest that HPV vaccines "might have benefits beyond prevention of anogenital cancers," she added.

The study looked at just four serotypes thought to cause most oral and anogenital cancers, but a new vaccine introduced in 2016 contains those four and an additional five.

One objection sometimes raised in the discussion of HPV vaccines is based on the normal immune response to the virus: in most cases, the infection is cleared relatively quickly. Gillison said the difficulty is that there's currently no way to tell who will clear the virus, and who will go on to have a chronic infection and therefore be at risk for cancer.

"That's why there is a current recommendation for universal vaccination of young girls and boys," she told 木瓜直播.

The study is evidence that the vaccine is effective in preventing oral infection, which renders the immune response unnecessary, commented Richard Schilsky, MD, ASCO senior vice president and chief medical officer.

"The bottom line [is that] the vaccine works if you get it but if you don't get it, it can't help you," he told 木瓜直播.

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