Tuesday October 16 2012
Teen sexual behaviour 'unchanged by HPV vaccine'
‘Sex is not a side effect of HPV vaccine’, reports the Daily Mail, while The Guardian tells us that ‘HPV vaccine not linked to sexual promiscuity in girls.’
The study appears to be prompted by concerns that the human papilloma virus (HPV) vaccine would lead to an upsurge in teenage sexual promiscuity.
The HPV vaccine is part of the national vaccination programme in England and is usually given to girls in year 8 (then aged 11-12 years) to help prevent cervical cancer.
Some strains of HPV, which can be spread through sexual contact, can trigger abnormal cell growth which can eventually lead to the development of cervical cancer.
The news is based on a US study that aimed to investigate the association between the human papilloma virus (HPV) vaccine and sexual activity-related outcomes among 1,398 girls. The researchers compared a group of 11 and 12 year olds who had the HPV vaccine to a group the same age that had not. Over the course of the next three years, they investigated whether there were differences between the groups in those that had been tested for, or diagnosed with pregnancy or a sexually transmitted infection (STI), or had been counselled about contraceptives.
The study found no association with increased sexual activity outcomes such as pregnancy, STI diagnosis, or a combination of these and sexual health or contraceptive counselling. A separate UK study published in July had similar findings.
Below the age of 16, you are not able to legally consent to sex. However, the reality is that it does happen, and teenagers would well advised to get both educated and vaccinated. For more information, see are you ready for sex?
Where did the story come from?
The study was carried out by researchers at Kaiser Permanente and Emory University in Atlanta, US. No external funding is reported by the study, although three of the study’s four co-authors report having received funding from pharmaceutical company Merck, makers of the US vaccine.
The study was published in the peer-reviewed medical journal Pediatrics.
The researchers say no studies that avoid the risk of bias from certain study designs (cross-sectional studies) have looked at this research question before.
Newspapers reported the results of the study fairly, though the Daily Mail seems to be suffering from a form of memory loss that commonly afflicts newspaper journalists. In the current article it mentions 'critics who claim the vaccine acts as a 'gateway' to sex’, without mentioning some of it’s own previous headlines, which included ‘GPs attacked for giving jab that campaigners say encourages underage sex’.
What kind of research was this?
This was a retrospective cohort study looking at sexual activity-related outcomes among girls after adolescent HPV vaccination.
Cohort studies are useful for looking at possible associations between various factors (such as HPV vaccination) and health outcomes (including sexual activity-related outcomes, such as pregnancy or STIs). They enable researchers who follow large groups of people for many years to look back at events which occur after the exposure (to a vaccine), but they cannot, on their own, establish cause and effect. A retrospective study relies on data on exposures or outcomes collected in the past (through medical records or as part of another study), or on people remembering what happened to them in the past.
Data used in this way may not be as reliable as data collected prospectively (when the data is collected specifically for the study, as events happen) as it relies on the accuracy of records made at the time and on people’s recall of events in the past, which can be inaccurate (referred to as recall bias). However, as the vaccines were given by a large US healthcare provider, the records in this case are likely to be reasonably reliable.
What did the research involve?
The study included 1,398 girls aged from 11 to 12 years, who were enrolled in the Kaiser Permanente Georgia health plan in metropolitan Atlanta in 2006/2007. Of these girls, 493 received at least one dose of the HPV vaccine (three doses are recommended) during the study period and 905 girls, who acted as the comparison group, received other recommended vaccines that did not include the HPV vaccine.
Both groups of girls were involved in the study through to 2010 and it examined whether they had been:
- tested for, or diagnosed with, pregnancy
- an STI
- counselled about contraceptives
The researchers specifically looked at girls of this age as it was the recommended age for HPV vaccination. The researchers also noted that this group were chosen to focus on girls who ‘were less likely to have already entered sexual activity’. The study period was chosen as it was during the first 18 months of the HPV vaccine becoming available.
The researchers analysed their results and adjusted for health-seeking and demographic characteristics for any differences seen at baseline between the groups. They excluded contraceptive counselling given to girls for painful menstruation or for acne.
What were the basic results?
The average age of girls who were tested, diagnosed, or counselled, was similar between the two groups: 14.4 years in the HPV group and 14.6 years in the comparison group.
The key finding of this study was that girls who received HPV vaccine did not have significantly higher incidence rates of pregnancy, STI infection testing, diagnosis, or contraceptive counselling compared to girls who did not receive HPV vaccine:
- adjusted incidence rate ratio: 1.29, 95% confidence interval [CI]: 0.92 to 1.80:
- incidence rate difference 1.6/100 person years, 95% confidence interval: -0.03 to 3.24
The confidence intervals here indicating that any small difference in the groups could have occurred by chance.
How did the researchers interpret the results?
The researchers conclude that HPV vaccination given at the recommended ages for girls (11 and 12 years) was not associated with an increased rate of sexual activity–related outcomes.
In a press release issued by Kaiser Permanente lead researcher Robert Bednarczyk said, ‘our study found a very similar rate of testing, diagnosis and counselling among girls who received the vaccine and girls who did not. We saw no increase in pregnancies, sexually transmitted infections, or birth control counselling – all of which suggest the HPV vaccine does not have an impact on increased sexual activity’.
Overall, this study provides some evidence that HPV vaccination given to adolescent girls aged 11 and 12 years is not associated with increased sexual activity-related outcomes over the following three years. The researchers note that their findings are based on the assumption that adverse outcomes (negative outcomes) after initiation of sexual activity would be followed by seeking healthcare.
In other words, this research was unable to identify girls who initiated sexual activity and did not seek reproductive healthcare, indicating that the research may have missed some girls who were sexually active.
The researchers also note that as only 11 and 12 year old girls were included in the study, it may be difficult to generalise these findings to groups outside of this age range and that further studies are needed for different age ranges.
In conclusion, this research does not alter the current advice in the UK for girls to receive the HPV vaccination. The vaccine is advised in an attempt to reduce the number of cervical cancer cases in the UK. This conclusion is supported by a similar recent UK study of HPV vaccination of older girls – see ‘Further reading’ for more information
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on twitter.