However, out-of-pocket vaccination costs influenced vaccine uptake, and researchers observed substantial disparities across socioeconomic status.
“Prophylactic HPV vaccination programs [have been] launched with aim to prevent cervical cancer as well as other HPV-related cancers,” Lisen Arnheim-Dahlström, PhD, research associate at the department of medical epidemiology and statistics at Karolinska Institutet in Stockholm, and colleagues wrote. “As the current vaccinated cohorts in Sweden are still too young to assess effectiveness of vaccination against precancerous lesions or invasive HPV-related cancers, condyloma acuminata, also referred to as genital warts, with a shorter incubation time after HPV infection, is ideal to study as a first evaluation of HPV vaccine effectiveness.”
Sweden introduced opportunistic HPV vaccination in 2007. The effort allowed girls ages 13 to 17 years the chance to receive the vaccination at a reduced price.
To evaluate the efficacy of HPV vaccines at various vaccination ages, Arnheim-Dahlström and colleagues examined a cohort of females aged 10 to 44 years living in Sweden who were linked to multiple population registers to identify genital warts incidence in relation to HPV vaccination.
Self-selection for vaccination in relation to condylomata risk was examined by studying condylomata rates over time among unvaccinated individuals. The researchers estimated incidence rate ratios of condylomata using time-to-event analyses adjusting for attained age and parental education. They also stratified the results by age at first vaccination.
Arnheim-Dahlström and colleagues reported that 124,000 women were vaccinated between 2006 and 2010, 90% of whom were in the subsidized target group. Higher parental education level was found to be a strong determinant of vaccination (RR=15.45; 95% CI, 14.65-16.30).
In females aged at least 20 years, condylomata rates declined among unvaccinated women, indicating that HPV vaccines were preferentially used by women at high condylomata risk. Vaccination effectiveness for women vaccinated younger than age 20 years was 76%; however, women vaccinated before aged 14 years demonstrated the highest vaccine effectiveness, with a 93% decrease in condyloma.
The HPV vaccine has been part of Sweden’s general vaccination program since 2012, making it available for free to all girls ages 10 to 12 years old. Catch-up vaccinations also are offered to those aged 13 to 18 years.
“Our study supports the notion that the vaccine should be given at young age,” Arnheim-Dahlström said in a press release. “When the vaccine was offered at a reduced price, the distribution was very unequal. Now that the vaccine is free and offered through the schools, it will be more evenly distributed in the population.”
In addition, the researchers reported that it was 15 times more common for daughters of academically educated parents to vaccinate themselves than for the daughters of less-educated parents. The educational level of the mother exhibited the most significant effect — girls were eight times more likely to be vaccinated if their mother was academically educated and four times more likely if the father was academically educated.