Five years after HPV vaccine introduction: Significant decline in HPV prevalence
Research findings
|Updated
The first cohort of girls offered the HPV vaccine in the 7th grade has a significantly lower prevalence of human papillomavirus (HPV) than girls in older cohorts who were not eligible for HPV vaccination through the immunisation programme. This is shown in a study from the Norwegian Institute of Public Health published in 2018.
National surveillance programme
The study is part of the national surveillance of the HPV vaccination programme run by the Norwegian Institute of Public Health. Since 2011, girls from various birth cohorts have been invited to participate in the studies at the age of 17, 21 and 25.
In this study, HPV prevalence in urine samples from the first birth cohort of girls offered the HPV vaccine through the childhood immunisation programme in 7th grade (born in 1997), was compared with the prevalence in samples from girls born in 1994 and 1996 who were not eligible for the HPV vaccine. Both groups provided samples when they were 17 years old. In total, urine samples from almost 18,000 girls were analysed for 37 different types of HPV.
Significant reduction in HPV prevalence
The combined prevalence of the 37 different HPV types was 19.9 per cent among girls born in 1994 and 11.4 per cent among girls born in 1997.
The prevalence of the HPV types included in the vaccine (6, 11, 16, and 18) was 7.4 per cent among girls born in 1994 and 1.4 percent among girls born in 1997. For the 1997 cohort (including both vaccinated and unvaccinated girls), the prevalence of all HPV types combined was reduced by 42 per cent, while the types included in the vaccine were reduced by 81 per cent.
"These are very encouraging results and support findings in several studies from other countries regarding the effectiveness of the HPV vaccine," says the study's lead author, Berit Feiring at the Norwegian Institute of Public Health.
Vaccinated versus unvaccinated
We also compared the data from unvaccinated girls born in 1994 with data from vaccinated girls born in 1997. The prevalence of the HPV types included in the vaccine was 7.7 per cent among unvaccinated girls, while it was only 0.8 per cent among vaccinated girls. This represents a reduction of 90 per cent.
Among the unvaccinated girls born in 1997, the prevalence of the vaccine types was 3.5 per cent, which is 54 per cent lower than among unvaccinated girls born in 1994.
"The decline we see among girls who have not received the vaccine is due to herd immunity," explains Feiring.
The study also analysed urine samples from girls born in 1996. This birth cohort was not offered the HPV vaccine through the childhood immunisation programme. However, the prevalence of HPV had still decreased in these girls compared to girls born in 1994. Since girls born in 1996 are only one year older than the first vaccinated cohort, this decline may be interpreted as an expression of herd immunity.
Protection also against other HPV types than those covered by the vaccine
The study also shows a 68 per cent reduction in the combined prevalence of HPV types 31, 33, and 45. These HPV types are not included in the vaccine. This means that the vaccine also protects against other types of HPV than those included in the vaccine, indicating cross-protection.
Reductions were also observed for several other individual HPV types not included in the vaccine, including HPV 52 (51 per cent reduction) and HPV 58 (32 per cent reduction). Reduction in the prevalence of non-vaccine types was also observed among unvaccinated girls, indicating herd protection for non-vaccine types as well.
About the study
Approximately 20 per cent of the girls in the birth cohorts of 1994, 1996, and 1997 participated and delivered a urine sample at the age of 17. The urine samples were analysed for HPV at the National Reference Laboratory for HPV at Akershus University Hospital. Data on HPV vaccination were obtained from the National Immunisation Registry (SYSVAK) and linked to the HPV results in order to compare the results for vaccinated and unvaccinated girls. The HPV vaccine Gardasil, which includes HPV types 6, 11, 16, and 18, was used in Norway during the study period. The study is based on repeated cross-sectional studies.
Full article: Feiring B, Laake I, Christiansen IK, Hansen M, Stålcrantz J, Ambur OH, Magnus P, Jonassen CM, Trogstad L. Substantial decline in prevalence of vaccine-type and non-vaccine type HPV in vaccinated and unvaccinated girls 5 years after implementing HPV vaccine in Norway Journal of Infectious Diseases 2018; 16. July 2018
This is a translation of the news article published in Norwegian in 2018.
