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 to 12 years compared to 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 pre-debut vs post-debut recipients than a lower immune response [among older recipients]," lead study author Didem Egemen, PhD, National Cancer Institute, Rockville, Maryland, told Medscape Medical News 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 October 21 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 (pre-debut group), and those who had been vaccinated after their sexual debut (post-debut 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% CI, 4% to 7%) in the unvaccinated group to 3% (95% CI, 1% to 6%) in the post-debut group and to less than 1% (95% CI, <1% to 1%) in the pre-debut group, Egemen and colleagues report
In real percentages, the prevalence of HPV 16 and 18 was 89% lower in the pre-debut group (P < .001) but only 41% lower in the post-debut 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 to 12 years (P = .08).
In the current study, 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% to 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.
Vaccination Rates Increasing
Asked to comment on the findings, Rebecca Perkins, MD, professor of obstetrics and gynecology at Boston University Chobanian and Avedisian School of Medicine, Boston Medical Center, Massachusetts, pointed out that the investigators evaluated data from 2011 to 2018. "We know that HPV vaccination rates have increased over that period and continue to increase," she emphasized in an email to Medscape Medical News.
Physicians also know that more persons are being vaccinated between the ages of 9 and 12 than was the case at the beginning of this study. "This is good news," she said, "as it means that more adolescents now in 2022 are benefiting fully from vaccination than they were in 2011," she added.
At the same time, Perkins acknowledged that many persons are still missing out on the chance to receive the vaccine on time — which means they are missing out on the chance to prevent cancer.
"Making sure that all adolescents receive vaccination between the ages of 9 to 12 has the potential to prevent up to 40,000 cancers every year in the US, [including] the most common HPV-related cancers, such as cervical cancer in women and tongue and tonsillar cancer in men," Perkins noted.
"Thus, it's critical that doctors and parents get the message that you can't vaccinate too early, only too late," she emphasized
Edgman and Perkins report no relevant financial relationships.
JAMA Netw Open. Published online October 21, 2022. Full text
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Cite this: HPV Vaccine Effectiveness Dependent on Age at Receipt - Medscape - Nov 07, 2022.