Introduction of the quadrivalent human papillomavirus (HPV) vaccine was associated with significant declines in the incidence of vaccine-type virus both in vaccinated and unvaccinated young women, according to a study published in Pediatrics.
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Four surveillance studies, conducted between 2006 and 2017, examined the rate of positive tests for vaccine-type HPV among 1,580 vaccinated and unvaccinated women aged 13-26 years. The majority of participants identified as African American or multiracial.
Overall, 97% of study participants received the quadrivalent vaccine, with vaccination rates increasing from 0% to 84% over the four waves of vaccination. Vaccine effectiveness – representing the relative risk of infection in vaccinated individuals, compared with unvaccinated risk before introduction of the vaccine – increased by 72% from wave 1 to wave 2, 91% from wave 1 to wave 3, and 80% from wave 1 to wave 4.
Among women who were vaccinated, rates of the quadrivalent vaccine–type HPV decreased by 81%, from 35% to 7%. But even among women who were unvaccinated, detection of the vaccine-targeted strains of HPV decreased by 40%, from 32% to 19%.
Chelse Spinner of the University of Cincinnati and her coauthors wrote that the decline in the quadrivalent vaccine–type HPV provided evidence of direct protection and high vaccine effectiveness in this real-world setting.
“This degree of effectiveness is remarkable given the fact that vaccination was defined as having received one or more doses (i.e., was not defined as having completed the vaccination series) and that women in this study were likely at a substantially higher risk for preexisting HPV infection than [were] those in the HPV vaccine clinical trials because of their reported sexual behaviors,” they wrote. “As noted in a recent review, evidence about herd protection will be a key component of cost-effectiveness analysis evaluating cervical cancer screening strategies.”
Twelve percent of women in the studies received the nine-valent HPV vaccine, and among these women, the rate of infection with the nine-valent vaccine-type HPV decreased from 47% in the first wave of vaccination to 14% in the last wave, representing a 71% decline.
The proportion of vaccinated women in the study who were infected with one or more of the five viral subtypes included in the nine-valent but not in the quadrivalent vaccine decreased significantly by 69%, from 23% to 7%.
However, these data also suggested a nonsignificant 58% increase among unvaccinated women in infections with one of the five subtypes covered by the nine-valent vaccine but not the quadrivalent vaccine.
Ms. Spinner and her associates noted this increase was unexpected and suggested the increase may be caused by the differences between vaccinated and unvaccinated women.
“For example, if women who are unvaccinated versus women who are vaccinated are more likely to practice riskier behaviors that would increase their risk of acquiring HPV, they would be more likely to acquire non–vaccine-type HPV,” they wrote.
Ms. Spinner graduated from the University of Cincinnati and now is a graduate student at the University of South Florida, Tampa. The study was funded by the National Institutes of Health. Darron R. Brown declared shares of Merck, but the other coauthors declared no other relevant financial disclosures.
SOURCE: Spinner C et al. Pediatrics. 2019, Jan 22. doi: 10.1542/peds.2018-1902.