Strains of HPV Decrease Due to HPV Vaccination, Study Finds
The findings reinforce the effectiveness of the HPV vaccine in preventing cervical cancer.
Two strains of human papillomavirus (HPV) originally targeted by vaccination since 2006 have declined since its introduction, according to an analysis of cervical precancers over a period of 7 years.
Investigators from the CDC Human Papillomavirus (HPV) Vaccine Impact Monitoring Project (HPV-IMPACT) sought to determine whether HPV types 16 and 18, which are responsible for approximately 70% of cervical cancers worldwide, are also decreasing. These 2 types have been targeted by the quadrivalent HPV vaccine, which was most typically administered in the United States between 2006 and 2015, and by the 9-valent vaccine that is the only vaccine currently administered in the United States.
The team analyzed more than 10,000 achieved specimens collected between 2008 and 2014 from women aged 18 to 39 diagnosed with grade 2 or 3 cervical intraepithelial neoplasia or adenocarcinoma in situ (CIN2+), precancerous conditions which can arise from persistent HPV infection and can lead to cervical cancer. Samples for 37 HPV types were then tested, and authors analyzed the proportion and estimated the number of cases by HPV types over time.
The findings of the investigation, published in Cancer Epidemiology, Biomarkers & Prevention, suggest that HPV vaccination reduced the incidence of infections that could lead to cervical cancer. The researchers found that the number of cases of CIN2+ reported to HPV-IMPACT declined by 21%. The estimated number of cases attributed to HPV 16/18 declined from 1235 in 2008 to 819 cases in 2014.
Furthermore, the study found:
- Among women who were vaccinated, the proportion of CIN2+ cases that were HPV 16/18-positive declined from 55.2% to 33.3%.
- Among unvaccinated women, the proportion of CIN2+ cases that were HPV 16/18-positive declined from 51.0% to 47.3%.
- Among those with unknown vaccination status, from 53.7% to 45.8%.
According to the press release, some vaccinated women were most likely HPV 16/18-positive because they were infected with these HPV types before they were vaccinated.
Researchers noted there were exceptions to declines in the proportion of CIN2+ cases that were HPV 16/18-positive in the oldest group, aged 35 to 39 years, due to their lack of eligibility for vaccination. Hispanic and Asian women also did not see a decline in the proportion, with the authors’ assumption that the women in those groups may have been less likely to be vaccinated. However, as of 2016, HPV vaccine uptake was robust in Hispanic and Asian teens; therefore, racial and ethnic disparities are expected to diminish, according to the press release.
According to the press release, 49.5% of girls and 37.5% of boys aged 13 to 17 are up-to-date on all recommended doses of the HPV vaccine. Nancy McClung, PhD, RN, epidemic intelligence service officer at the CDC in Atlanta, suggested that clinicians should continue to strongly recommend the HPV vaccine for all preteens at age 11 or 12, and effectively answer parents’ common questions about the vaccine.
“This is clear evidence that the HPV vaccine is working to prevent cervical disease in young women in the United States,” said Dr McClung. “In the coming years, we should see even greater impact as more women are vaccinated during early adolescence and before exposure to HPV.”