Is 1 Dose Enough for HPV Vaccination?

The demand for vaccines that protect against human papillomavirus (HPV) outpaces supply in many countries.

In December 2019, the problem was recognized to the extent that the World Health Organization (WHO) Strategic Advisory Group of Experts on immunization went as far as recommending the suspension of vaccination of boys until all girls who need the vaccine can get it.

In this context, the possible efficacy of administering just 1 dose of prophylactic HPV vaccine has become a question of clinical importance. The team behind a new retrospective study published in Cancer has provided more evidence that a single HPV vaccine dose may be effective in preventing cervical cancer.

The retrospective matched cohort study was conducted using data taken from Optum’s Clinformatics DataMart Database.

The investigators used the Optum database to identify female patients between 9 and 26 years of age who had received 1 or more doses of quadrivalent HPV vaccine between January 2006 and June 2015.

All patients included in the analysis had a Papanicolaou test a >1 year after their matched case’s final dose.

Cox proportional hazards models were used to compare the number of HPV vaccine doses each patient received with the incidence of preinvasive cervical disease and high-grade cytology. At 5-year follow-up, the Kaplan-Meier method was used to estimate cumulative incidence rates.

The study ultimately included 133,082 female patients, 66,541 of whom were vaccinated and 66,541 whom were unvaccinated.

In female patients between 15 and 19 years of age, the hazard ratio for high-grade cytology among the 3-dose group was 0.84 (95% confidence interval [CI], 0.73-0.97).

The hazard ratios for preinvasive cervical disease were 0.64 (95% CI, 0.47-0.88), 0.72 (95% CI, 0.54-0.95), and 0.66 (95% CI, 0.55-0.80) for the 1-, 2-, and 3-dose groups respectively.

In female patients aged 15-19 years, HPV vaccination with any number of doses was associated with a lower risk of preinvasive cervical disease.

“The unadjusted event rate at year 5 for the unvaccinated group was 2.65%, whereas the rates for the 1, 2, and 3 dose groups were 1.62%, 1.99%, and 1.86%, respectively,” study authors wrote.

The study team reported that there was a similar degree of association between the varying doses of quadrivalent HPV vaccine and the presence of preinvasive cervical lesions. They encouraged future studies to confirm their findings.

They also pointed out, however, that HPV-related disease remains a significant burden. Among women who receive the vaccine at an older age, there is a higher likelihood of already having been exposed to HPV.

“Efforts should focus on not only the need to initiate the HPV vaccine but also the need for beginning and continuing cervical cancer screening among young women who are vaccinated at older ages,” the investigators of the study concluded.