The introduction of an HPV vaccination program in Norway resulted in a significant decrease in vaccine and nonvaccine genotypes in both vaccinated and unvaccinated adolescent girls, according to findings published in The Journal of Pediatrics.
“In Norway, the HPV vaccine has been offered in a school-based immunization program with single-cohort delivery to 12-year old girls since 2009,” Berit Feiring, MScPharm, of the department of infectious disease epidemiology and modeling at the Norwegian Institute of Public Health, and colleagues wrote. “In contrast to most Western countries, no catch-up vaccination of older girls was initially offered.”
According to Feiring and colleagues, previous clinical trials in women between the ages of 16 and 26 years showed vaccination was more effective in HPV-naive populations than in all vaccinated groups. These results, according to the researchers, exemplify that vaccination does not protect as effectively against current infection.
To better understand the effects of the Norwegian vaccination program, Feiring and colleagues examined the rates of HPV among two groups of girls born in 1994 and 1996 who did not receive the vaccine and one group born in 1997 who received vaccination against HPV. Urine samples were tested for 37 different genotypes of the infection.
Of the 17,749 samples analyzed, the rate of any HPV type decreased by 42% when girls were vaccinated (95% CI, 37%-47%). A larger decrease — 81% — was observed in the vaccinated group against vaccine genotypes when compared with those born in 1994 (95% CI, 76%-85%).
Reduced rates of vaccine-type HPV were also observed in those who were unvaccinated, with a 54% decrease observed in girls in the 1997 cohort who were unvaccinated (95% CI, 39%-66%) and a 90% decrease in girls in the 1997 who were vaccinated (95% CI, 86%-92%) when compared with girls in the 1994 group.
The researchers observed a reduction in vaccine-type HPV in those within the 1997 group who were vaccinated (77%) compared with unvaccinated girls in this group (95% CI, 65%-85%). Girls within this group also had a reduction in the prevalence of nonvaccine type HPV. Feiring and colleagues noted that these include low-risk type, possibly/probably high-risk types and high-risk types 31, 33, 39, 45, 51 and 59.
“The early impact of the HPV immunization program in this largely HPV-naive Norwegian population seems more beneficial than anticipated upon introduction of the vaccine in 2009, but more effectiveness studies in HPV-naive populations are needed to confirm the findings,” they wrote. “With the growing amount of evidence for sustained long-term protection of the HPV vaccine, we feel optimistic that the observed reduction in HPV prevalence in urine samples may translate into a future decline in the incidence of precancerous lesions and cervical cancer in Norway.” – by Katherine Bortz
Disclosures: The authors report no relevant financial disclosures.