The effectiveness of the human papillomavirus (HPV) vaccine against HPV types 16 and 18 is highly dependent on the age at which it is given. Prevalence rates have been shown to be significantly lower among girls who are vaccinated at the recommended ages of 9-12 years, compared with those who are vaccinated after their sexual debut, data from the National Health and Nutrition Examination Survey (NHANES) indicate.
“HPV vaccination does not have any therapeutic effect on HPV infections already acquired, which is more likely to explain the difference in prevalence between predebut versus postdebut recipients than a lower immune response [among older recipients],” lead study author Didem Egemen, PhD, National Cancer Institute, Rockville, Md., told this news organization in an email.
“Still, among older females, the immune response of the vaccine is likely to still be quite strong, and we would encourage vaccination [of female patients] if unvaccinated, as our paper showed that vaccination post debut will still reduce HPV 16/18 prevalence by half,” she added.
The research letter was published online in JAMA Network Open.
National sample evaluated
Using data from NHANES, a biennial, cross-sectional sample (cycles 2011 through 2018), the researchers identified female persons who were aged 26 years or younger in 2006, when HPV vaccination was introduced, and who were eligible for routine vaccination or “catch-up” vaccination (given between the ages of 13 and 26 years), as per recommendations from the Advisory Committee on Immunization Practices. The investigators then compared the prevalence of HPV types 16 and 18 among unvaccinated female patients, female patients who had been vaccinated prior to their sexual debut (predebut group), and those who had been vaccinated after their sexual debut (postdebut group).
They also estimated vaccine uptake among those who were eligible for routine vaccination, as well as the proportion of vaccinated female patients with respect to racial and ethnic subgroups.
In the overall cohort, the prevalence of HPV types 16 and 18 decreased by 6% (95% confidence interval, 4%-7%) in the unvaccinated group to 3% (95% CI, 1%-6%) in the postdebut group and to less than 1% (95% CI, <1%-1%) in the predebut group, Dr. Egemen and colleagues report.
In real percentages, the prevalence of HPV 16 and 18 was 89% lower in the predebut group (P < .001) but only 41% lower in the postdebut group (P = .29) compared with unvaccinated female patients. And compared with female patients who were vaccinated after their sexual debut, the prevalence of HPV 16 and 18 was reduced by 82% among those who had received the vaccine at the recommended ages of 9-12 years (P = .08).
In the current study, Dr. Egeman acknowledged that only 38% of ever-eligible female patients received the vaccine, although the prevalence increased to 56% when only female patients who were eligible for routine vaccination were taken into account. On the other hand, only 21% (95% CI, 14%-28%) of female patients eligible for routine vaccination received their first dose by age 12 years.
Indeed, the mean age on receipt of the first vaccination dose was 14.5 years (95% CI, 14.1-14.8 years), the authors note, and only 59% of girls received their first dose prior to their sexual debut. Additionally, among routine vaccination–eligible girls aged 12 years or younger in 2006, 33% were vaccinated before and 23% after their sexual debut, and the rest were not vaccinated.
Interestingly, differences in the age at which the HPV vaccine was received by race and ethnicity were negligible, the investigators point out.