Vaccinating teenage girls to protect against a virus that causes cervical cancer doesn’t increase risky sexual behaviours, as some parents have feared, indicates a new study in the Canadian Medical Association Journal. 

The human papilloma virus (HPV) causes an estimated 70 per cent of cervical cancers, and most anal and genital warts.

Since 2006, an HPV vaccine has been licensed in countries including Canada to protect against four types of the virus. But there have been concerns that the vaccine might give girls and women a false sense of security, and encourage promiscuity.

HPV vaccination of girl

Canadian researchers their study is the largest look at the association between HPV vaccination and clinical indicators of sexual behaviour. (Jessica Rinaldi/Reuters)

Researchers from Montreal and Kingston, Ont. followed a group of more than 260,000 girls. About half were eligible to receive HPV shots when Ontario introduced a vaccination program to Grade 8 students in 2007 and 2008.

Dr. Leah Smith of the department of epidemiology, biostatistics and occupational health at McGill University in Montreal and her team examined data on vaccine receipt, as well as on indicators of sexual behaviour, specifically pregnancy and non-HPV-related sexually transmitted infections.

HPV vaccination and eligibility for the program did not increase the risk of pregnancy or the STIs among females aged 14 to 17, the researchers found.

"We present strong evidence that HPV vaccination does not have any significant effect on clinical indicators of sexual behaviour among adolescent girls," the study’s authors conclude in Monday’s CMAJ issue.

"These results suggest that concerns over increased promiscuity following HPV vaccination are unwarranted and should not deter from vaccinating at a young age."

They found nearly six per cent of the girls, who were followed over about four years,  become pregnant or contracted a sexually transmitted infection (STI). Overall, 10,187 pregnancies and 6,259 cases of STIs were documented.

The researchers say it’s the largest study on the association between HPV vaccination and clinical indicators of sexual behaviour.

Uptake of HPV vaccination in females ranges from 60 per cent to 85 per cent, according to Immunize Canada, which promotes the understanding and use of vaccines recommended by a federal committee.

In 2012, researchers published a study of nearly 1,400 girls in Atlanta directly comparing vaccinated and unvaccinated females, and reported similar results.

Public controversy has focused on direct measures of sexual behaviour such as the number of sexual partners or condom use, the researcher said. Instead, they measured pregnancy and sexually transmitted infections to determine the health consequences of risky sexual behaviour, which they say are arguably at least as important in public-health terms than the direct measurements.

The most common side-effect of the vaccination is pain at the injection site, fainting or dizziness.

No deaths or diseases have been causally linked to either of the two HPV vaccines, Gardasil or Cervarix, said Jane Kim, an associate professor of Health Decision Science at the Harvard School of Public Health in Boston, who was not part of the new study.

The study was funded by the Canadian Institutes of Health Research, with support from the Institute for Clinical Evaluative Sciences.

With files from Reuters