Alicia Ault

May 18, 2016

WASHINGTON, DC — There has been a decrease in the prevalence of high-risk types of human papillomavirus (HPV) in the United States since the HPV vaccination was introduced, but cross protection and herd immunity remain low, according to a new study.

This lack of strong herd immunity and cross protection is most likely related to the low vaccination rate, said Christopher Tarney, MD, from the Womack Army Medical Center in Fort Bragg, North Carolina.

"It's disturbing that such a small percentage of the population has been vaccinated" when the tools "to eradicate cervical cancer" are available, he told Medscape Medical News.

Dr Tarney presented his analysis of HPV prevalence here at the American Congress of Obstetricians and Gynecologists 2016 Annual Clinical Meeting.

He compared data from the National Health and Nutrition Examination Survey for women 18 to 29 years of age in 2003, before the introduction of the HPV vaccine, with three successive datasets from after 2006, the year of the introduction: 2007/08, 2009/10, and 2011/12.

Dr Tarney assessed 1628 women, representing some 21 million women, for the prevalence of HPV types 16 and 18 and other high-risk types, herd immunity, cross protection, and type replacement in vaccinated women.

In women who received at least one dose of the vaccine, the prevalence of high-risk HPV decreased from 67.0% in 2007/08 (95% confidence interval [CI], 50.7 - 81.4) to 41.5% in 2011/12 (95% CI, 30.5 - 53.1).

The prevalence of types 16 and 18, which are specifically targeted by the vaccine, declined from 10.1% in 2003, before the vaccine was introduced, to 4.2% in vaccinated women in 2011/12.

The data showed no statistically significant type substitution as a result of vaccination, Dr Tarney reported.

For unvaccinated women, the prevalence of high-risk HPV remained stable, at 49.5% in 2007/08 (95% CI, 42.5 - 56.6) and 50.8% in 2011/12 (95% CI, 43.0 -58.7).

Dr Tarney expressed frustration that there has not been much of an increase in vaccination rates in the United States in recent years. A 2014 survey showed that only 40% of girls 13 to 17 years of age had received all three recommended doses of HPV vaccine (MMWR Morb Mortal Wkly Rep. 2015;64:784-792).

The upward trend in vaccination rates and the decrease in the prevalence of the HPV types targeted by the vaccine are similar to rates reported in other countries that have HPV vaccination, said Kevin Ault, MD, from the University of Kansas Medical Center in Kansas City.

"It's a very consistent finding in multiple studies," he told Medscape Medical News.

But herd immunity and cross protection in the United States, as evidenced by Dr Tarney's analysis, are nowhere near as high as in some other nations, like Australia and Canada, Dr Ault reported.

In fact, for heterosexual men in Australia, genital warts have all but disappeared, likely because of the widespread vaccination of women in that country.

But in the United States, "the vaccine rate is quite low," Dr Ault explained. He said he believes that cross protection and herd immunity will improve with increasing vaccination rates and with the continued use of the nine-valent vaccine, which was introduced in 2014.

Both Dr Ault and Dr Tarney called on physicians to do more to increase awareness of the vaccination among their patients.

"Primary care physicians and specialists need to get the word out about the importance of these vaccines," Dr Tarney told Medscape Medical News. "We have the tools to prevent a really, truly preventable cancer."

Dr Tarney and Dr Ault have disclosed no relevant financial relationships.

American Congress of Obstetricians and Gynecologists (ACOG) 2016 Annual Clinical Meeting: Abstract 120P. Presented May 15, 2016.

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