HPV vaccine 'not linked to risky sexual behaviour in teenage girls'

Tuesday October 16 2018

"HPV vaccine does not make girls more likely to have risky sex," the Mail Online reports.

The current NHS human papilloma virus (HPV) vaccine is routinely offered to teenage girls in the UK.

It protects against 4 types of the sexually transmitted infection HPV, including the types that cause most cervical cancers.

The first dose of the HPV vaccine is offered to girls aged 12 and 13 in school year 8. The second dose is normally offered 6 to 12 months after the first (in school year 8 or year 9).

But there have been concerns among some groups that having the vaccine could be associated with increased sexual promiscuity.

One argument is the vaccine could increase the possibility of risky sexual behaviour because vaccinated girls may (mistakenly) think they're no longer at risk of getting a sexually transmitted infection (STI).

The Mail's headline was prompted by a survey carried out in British Columbia, Canada, where the vaccine was introduced in 2008.

Researchers compared sexual health surveys from 2003, 2008 and 2013, and found self-reported sexual activity actually decreased over the period.

For example, in 2003 21% of 15-year-old girls said they'd had sex, compared with 18% in 2013.

There was also a fall in the percentage of girls saying they'd had sex before the age of 14 and an increase in the use of condoms.

So the results find no evidence of an increase in promiscuity after the vaccine was introduced.

But the study has 2 key limitations.

Firstly, it can't prove that the introduction of the vaccine is in any way linked with the changes seen.

The decrease in self-reported sexual activity may just be down to increased sexual health awareness.

Secondly, we have no idea whether these results from British Columbia apply to the UK.

What we do know is that the HPV vaccine can save lives.

Find out more about the HPV vaccine

Where does the study come from?

The study was carried out by researchers from the University of British Columbia.

It was funded by the Canadian Institutes of Health Research.

The study was published in the peer-reviewed Canadian Medical Association Journal.

The Mail's coverage is accurate. But it could have made it clearer that the sexual health behaviour of teenagers in 1 region of Canada may not be representative of a similar population in the UK.

The news website does point out that the fall in sexual activity among teenage girls could be due to wider social trends that have little or nothing to do with HPV vaccination.

What kind of research was this?

This cross-sectional study looked at a series of adolescent health surveys that are completed in schools in British Columbia, Canada, every 5 or 6 years.

They wanted to see if sexual health behaviour had changed following the introduction of the HPV vaccine.

The licensed vaccines in Canada are Cervarix, Gardasil and Gardasil-9. All 3 protect against HPV 16 and 18.

Gardasil, the vaccine used in the UK, also protects against types of HPV associated with genital warts and other cancers, such as vulval and anal cancer.

As the researchers say, there are concerns that the HPV vaccine may encourage earlier sexual intercourse and having more partners.

This in turn may lead some parents to discourage their daughters from getting the vaccine.

What did the research involve?

The BC Adolescent Health Survey has been conducted since 1992 and is said to cover 1.4 million students enrolled in schools across the region.

The participation rate is said to be about 75% each year.

The anonymous survey covers sociodemographic information, health behaviours and exposure to risks.

It includes questions on sexual health behaviour, such as:

  • have you ever had sex
  • age when you first had sex
  • number of sexual partners within the past year
  • substance use before the last time you had sex
  • use of condoms last time you had sex
  • use of birth control pills last time you had sex
  • pregnancy

This study analysed surveys from 2003, 2008 and 2013.

The vaccine was introduced in September 2008, but as surveys are conducted from January to June of each year, only girls in the 2013 survey would have received the vaccine.

The study included a total of 302,626 girls, of whom 41% completed the 2003 survey, 33% the 2008 survey and 26% the 2013 survey. The average age of participants was 15.

This study only included girls who identified as heterosexual. Those identifying as lesbian or bisexual will be included in another study.

What were the basic results?

The number of girls saying they'd ever had sex fell over the years, from 21.3% in 2003 to 20.6% in 2008 and 18.3% in 2013.

Girls in 2013 (who'd had the vaccine) were around 10 to 20% less likely to report having had sex compared with girls in the previous 2 surveys.

Girls in 2013 were also around 25% less likely to report having had sex before the age of 14.

Use of condoms showed some sign of an increase, though the pattern was inconsistent: condom use was reported by 65.6% in 2003, 63.3% in 2008 and 68.9% in 2013.

Between 2003 and 2013 there was also a 9% increase in use of the oral contraceptive pill and a 42% decrease in reported pregnancies.

The number who said they'd had alcohol or taken other substances before sexual intercourse also decreased overall from 26% in 2003 to 19.3% in 2013.

How did the researchers interpret the results?

The researchers concluded: "Since the implementation of the school-based HPV vaccination program in BC, sexual risk behaviours reported by adolescent girls either reduced or stayed the same.

"These findings contribute evidence against any association between HPV vaccination and risky sexual behaviours."

Conclusions

The researchers' findings of no association between the introduction of the HPV vaccine and increased risky sexual health behaviour are encouraging.

The large number of participants in their study across each of the 3 years is a notable strength.

But the research has a number of important limitations.

The study may suggest that HPV vaccine isn't associated with increased promiscuity or risky behaviour.

But this doesn't mean that the introduction of the vaccine caused a decrease in more risky behaviour.

The decrease in risky behaviour that was observed may be due to increased sexual health awareness over time.

The researchers only looked at the results of 1 survey after the introduction of the vaccine.

This single assessment, 5 years after the vaccine was introduced, can't on its own provide sufficient evidence of the potential effects of the vaccine on health behaviour.

Ideally, follow-up over a number of years would be helpful to see if the pattern continues.

Because the surveys relied on self-reporting, there's always the possibility that some responses could be inaccurate.

It's even possible that increased sexual health awareness could make people more likely to give responses they feel they "should" be giving.

And the research was carried out in British Columbia, so we don't know that the results apply in the UK or elsewhere.

The NHS HPV vaccine is freely available to teenage girls aged between 12 and 18 years, and is routinely offered in school year 8 in England for girls aged 12 to 13.

It helps protect against cervical cancer, as well as a number of less common cancers.

Condoms remain the most effective way of protecting against STIs.

Analysis by Bazian
Edited by NHS Website