Early HPV vaccination provides the best protection
The HPV vaccine is most effective against high-grade cervical lesions if given before the age of 17, according to a new register-based study from Karolinska Institutet and the Public Health Agency of Sweden. The results, which are published in the International Journal of Cancer, show that the vaccine is effective at preventing high-grade lesions.
There are over 100 strains of the human papillomavirus (HPV). They are spread through physical contact, such as via sexual intercourse, and are highly infectious. At some point during our lives, most of us are infected with one or more HPV types, at least twelve of which are classed as high risk, since infection can cause cancer. Earlier population studies show that HPV vaccination is effective against both condyloma (an STD) and cervical lesions.
Cervical cancer is caused by HPV infection, with HPV types 16 and 18 responsible for some 70 per cent of cases. The same viral types are also behind a high proportion of cervical lesions, which can develop into an invasive cancer if left untreated. HPV types 16 and 18 are included in the HPV vaccine that has been used in Sweden since 2007. In 2012, an HPV vaccine was included in the national childhood vaccination programme, and girls between the ages of 10 and 12 are offered free vaccination through the school health service.
The researchers behind this new study have examined the effect of the HPV vaccine on high-grade lesions, with a particular focus on grade 2 and 3 cervical intraepithelial neoplasia (CIN), which can be a prodrome of cancer. The study included all females, 1.4 million individuals all told, between the ages of 13 and 29 living in Sweden at some point during 2006–2013, of whom just over 236,000 had been vaccinated. Details on vaccination, histologically confirmed high-grade lesions (CIN2 and CIN3) and other such data were collected using national healthcare registries.
Before the age of 17
Comparing the risk of high-grade lesions between the vaccinated and unvaccinated women, the researchers discovered that in those who were vaccinated before the age of 17, the effectiveness of the vaccine against high-grade lesions was 75 per cent. The protective effect dropped to 46 per cent for those vaccinated between the ages of 17 and 19, and again to 22 per cent for those vaccinated at or after the age of 20.
“Our conclusion is that the vaccine protects against serious prodromes of cervical cancer, with the greatest effect being when it’s given before the age of 16,” says principal investigator Lisen Arnheim Dahlström at Karolinska Institutet’s Department of Medical Epidemiology and Biostatistics.
The researchers will continue to study the effects of HPV vaccination on the population in the long term. One important line of inquiry is whether the vaccination programme has the expected effect against cervical cancer. The high-grade lesions examined in this new study can eventually develop into cancer, but it will be some years before the researchers can study the protection provided against cervical cancer.
The study was financed with grants from the Swedish Foundation for Strategic Research and the Strategic Research Area (SFO) in Epidemiology, Karolinska Institutet.
Text: Karin Söderlund Leifler (in translation from Swedish)
Quadrivalent HPV vaccine effectiveness against high-grade cervical lesions by age at vaccination: A population-based study
Eva Herweijer, Karin Sundström, Alexander Ploner, Ingrid Uhnoo, Pär Sparén, Lisen Arnheim-Dahlström
International Journal of Cancer, version of record online 9 March 2016, doi: 10.1002/ijc.30035