HPV Vaccine: How Many Doses Are Really Needed?

Two doses of the quadrivalent human papillomavirus (HPV) vaccine reduced the risk of genital warts, in particular among women who were younger than 17 years upon receiving the first vaccination, according to a population-based study in JAMA.

Two doses of HPV vaccine provided up to 71% protection against genital warts, while the standard 3-dose schedule provided protection up to 82%, the authors reported. 

Pertinent Points

- Two doses of quadrivalent HPV vaccine offered a rate of protection against genital warts of up to 71% in girls aged 10 to 16 at the time of their first dose, compared with a rate of up to 82% associated with the standard 3 doses.

- The number of cases prevented by receiving the third dose was relatively small at 59 per 100,000 person-years.

Although 3 doses produced the maximum reduction of risk, researchers found that 2 doses was associated with an incidence rate ratio of 0.29 for genital warts (95% CI, 0.21-0.40) among girls who were between ages 10 and 16 years at the time of their first dose. For girls who received 3 doses, the incidence rate ratio was 0.18 (95% CI, 0.15-0.22).

"Our results suggest that we should continue with the recommended three doses, but open up for a future two-dose schedule after more studies have been conducted regarding the protection against genital warts and initial stages of cervical cancer," said Lisen Arnheim Dahlström, of the department of medical epidemiology and biostatistics at Karolinska Institutet.

For the study, researchers reviewed the association between the number of doses of HPV vaccination and genital warts among 1 million girls and women aged 10 to 24 years living in Sweden and who were followed up between 2006 and 2010. The study used the Swedish nationwide population-based health data registers.

The authors suggested additional study is needed to understand the relationship between the number of vaccine doses and cervical cancer risk. While the primary goal of vaccination against HPV is to prevent cervical cancer, the researchers used an analysis of genital warts related to HPV types 6 and 11 as the earliest measurable preventable disease outcome for the quadrivalent HPV vaccine.

Among 20,383 new cases of genital warts, 322 happened after the girl received at least one dose of HPV vaccine, the researchers reported. One dose was associated with an incidence rate ratio of 0.31 (95% CI, 0.20-0.49), corresponding to an incidence rate difference of 384 cases per 100,000 person-years (95% CI, 305-464), compared with no vaccination.

Furthermore, the researchers reported that the number of cases prevented by receiving the third dose was relatively small at 59 per 100,000 person-years (95% CI, 2-117).

References:

Herweijer E, Leval A, Ploner A, et al. Association of varying number of doses of quadrivalent human papillomavirus vaccine with incidence of condyloma. JAMA. 2014;311:597-603.