Decrease in certain HPV types among unvaccinated women suggests herd protection
Prevalence of the four types of human papillomavirus (HPV) included in the original vaccine decreased most among women who were fully vaccinated but also decreased significantly among women who were unvaccinated between 2006 and 2017.
A surveillance study of human papillomavirus (HPV) trends in the years following introduction of the 4-valent and 9-valent vaccines found evidence of their effectiveness, as well as herd protection, which is the resistance to the spread of a contagious disease within a population resulting from a sufficiently high proportion of individuals who are immune to the disease.
Researchers recruited female participants who were 13 to 26 years of age from hospital-based and community health clinics from 2006 to 2017, the years after the introduction of HPV vaccines. Participants were included only if they had had oral-genital or genital-genital contact with a male or female partner.
Researchers collected four waves of data: wave 1 (2006 to 2007, n=371), wave 2 (2009 to 2010, n=409), wave 3 (2013 to 2014, n=400), and wave 4 (2016 to 2017, n=400). For 98% of participants, vaccination status was defined as having received at least one HPV vaccine dose confirmed through a state immunization registry or electronic health record; for the remainder, vaccination status was confirmed by self-report. Results were published by Pediatrics on Jan. 22.
Vaccination rates increased from 0% to 84.3% over the study period. Detection of the HPV types in the 4-valent vaccine decreased from 35% to 6.7% (80.9% decline; odds ratio [OR], 0.13 [95% CI, 0.08 to 0.22]) among women who were vaccinated and from 32.4% to 19.4% (40% decline; OR, 0.50 [95% CI, 0.26 to 0.97]) among women who were unvaccinated. Estimated vaccine effectiveness was 90.6% in wave 3 and 80.1% in wave 4. An exploratory analysis also found a significant decrease in the five additional HPV types targeted by the 9-valent vaccine among women who were vaccinated.
The significant decline in 4-valent vaccine-type HPV in women who were vaccinated and the high degree of vaccine effectiveness shown by the comparison of women who were vaccinated and those who were not suggests high vaccine effectiveness in a real-world setting, even among those who received only one dose rather than completing the series, the study authors said.
However, they cautioned that “the findings should not be interpreted as suggesting that current recommendations for a 2- or 3-dose series and vaccinating before sexual initiation are not necessary.” An exploratory analysis showed that getting one dose rather than all three was associated with 3.2 times the adjusted odds of vaccine-type HPV infection (P=0.04) and that young women who had sex before vaccination were more likely to be positive for vaccine-type HPV (8.8% vs. 3.8%, P=0.0021).
“Our findings of a decrease in vaccine-type HPV among women who were vaccinated extend the findings of those studies conducted over different time frames and in different populations and settings, and they support the real-world effectiveness of the 4-valent vaccine, especially in younger age groups and countries with high vaccination coverage,” the authors wrote.