HPV vaccine 'safe and effective', says review

Wednesday May 9 2018

"HPV vaccine for schoolgirls gets full marks," reports ITV News.

Almost all cases of cervical cancer, which usually takes many years to develop, are caused by the human papilloma virus (HPV). HPV causes the cells in the cervix to slowly go through a series of pre-cancerous changes that can eventually turn into cancer.

The HPV vaccine helps protect against cervical cancer by preventing the cells of the cervix from changing into pre-cancerous cells.

In this latest review, researchers pooled results from 25 trials worldwide involving more than 70,000 girls and young women. After looking at the evidence, the researchers reported that the HPV vaccine provides excellent protection against development of pre-cancerous cells in the cervix.

In the UK, cervical cancer affects more than 3,000 women a year, with most cases diagnosed between the ages of 25 and 29. In 2016, 815 women died of cervical cancer. A programme began 10 years ago to vaccinate schoolgirls aged 12 to 13 against HPV.

This review found that vaccinating girls before they have HPV works best, cutting their chances of getting pre-cancerous cells linked to the most dangerous strains, HPV16 and HPV18, by 99%. Vaccinating women aged 26 and over, and those who have already been infected, also cuts their chances of pre-cancerous cells but not as dramatically.

The researchers found no increased risk of miscarriage or other serious adverse events in the years following vaccination.

Find out more about the HPV vaccine.

Where did the story come from?

The study was carried out by researchers from the Belgian Cancer Centre and the University of Antwerp, both in Belgium, and Lancashire Teaching Hospitals NHS Trust in the UK as part of the worldwide Cochrane Collaboration of research. It was funded by the National Institute of Health Research, European Cancer Network, Belgian Foundation Against Cancer, IWT (a Belgian science and technology institute) and the CoheaHr Network (part of the European Commission).

It was published by the Cochrane Collaboration and is free to read online.

The UK media celebrated the news that the vaccine is safe and works well, with ITV News asking: "Is it now time for boys to get it too?"

Boys are currently not routinely offered the vaccine, although some people have pressed for the programme to be extended. While boys do not get cervical cancer, they can pass HPV on to unvaccinated girls. The virus can also cause less common cancers of the throat, anus and penis.

What kind of research was this?

This was a systematic review and meta-analysis of randomised controlled trials. This is the best way to find out whether a treatment works.

Carrying out a meta-analysis means researchers can pool evidence from smaller trials to come up with a more reliable result.

What did the research involve?

Researchers looked for randomised controlled trials that compared the HPV vaccine with a dummy vaccine (placebo) and measured how many girls or young women had pre-cancerous cells (called cervical intraepithelial neoplasia) at grade 2 or above.

They also wanted to assess the vaccine's effectiveness against the most dangerous strains, HPV16 and HPV18, which are thought to cause around 70% of all cervical cancers. The UK vaccination programme protects against both.

The 26 studies included 73,428 girls and women, mostly aged 15 to 26, with follow-up periods from 0.5 to 8 years. The researchers looked separately at results for:

  • girls or women who had no HPV infection when vaccinated
  • women aged over 26
  • the 2 different types of HPV vaccine, which protect against different strains

As well as looking for evidence of pre-cancerous cells, they checked for differences in rates of serious adverse events and pregnancy outcomes between women given the HPV vaccine and women given a placebo.

Unfortunately, results for cervical cancer were not available.

All the studies were assessed for risk of bias and, while all but one were funded by the vaccine manufacturers, the review's authors said most of the trials were at low risk of bias.

What were the basic results?

Results were clearest for girls and young women who had not been infected with HPV at the time they were vaccinated. These findings are likely to be the most relevant for girls in the UK, who receive the vaccine at an age where they are unlikely to have come into contact with HPV.

For non-infected girls and women:

  • chances of having pre-cancerous cells (CIN grade 2) linked to HPV16 or HPV18 reduced from 164 per 10,000 to 2 per 10,000 – a reduction in relative risk (RR) of 99% (RR 0.01, 95% confidence interval [CI] 0.00 to 0.05)
  • chances of having higher-grade pre-cancerous cells (CIN grade 3) linked to HPV16 or HPV18 reduced from 70 per 10,000 to 0 per 10,000 – a reduction in risk of 99% (RR 0.01, 95% CI 0.00 to 0.10)
  • chances of having pre-cancerous cells (CIN grade 2) linked to any strain of HPV reduced from 287 per 10,000 to 106 per 10,000 – a reduction in risk of 63% (RR 0.37, 95% CI 0.25 to 0.55)
  • chances of having higher-grade pre-cancerous cells (CIN grade 3) linked to any strain of HPV reduced from 109 per 10,000 to 23 per 10,000 – a reduction in risk of 79% (RR 0.21, 95% CI 0.04 to 1.10)

The rate of deaths was similar among vaccinated and non-vaccinated women – 11 per 10,000 in the control group and 14 per 10,000 in the vaccine group – and no deaths were linked to the vaccine.

The HPV vaccine did not increase the risk of miscarriage or pregnancy termination. However, there was not enough information to be sure about the risks of stillbirth or babies born with malformations.

How did the researchers interpret the results?

The researchers said: "There is high-quality evidence that HPV vaccines protect against cervical pre-cancer in adolescent girls and women who are vaccinated between 15 and 26 years of age."

They added that "protection is lower" when women are already infected with HPV at the time of vaccination.

Conclusion

This review provides reassurance for women and girls who have received the HPV vaccine, and for parents of girls due to receive it.

It found the vaccine does a good job of protecting against the most dangerous strains of HPV, which are passed on through sex and skin-to-skin contact of the genital areas.

The majority of the trials included in the review involved girls and women aged 15 to 26, which is slightly older than those vaccinated in the UK programme.

However, what made the key difference for the vaccine's effectiveness was whether or not women already had HPV when they were vaccinated. By vaccinating girls at age 12 to 13, the chances of them being already infected are lower, which should increase the effectiveness of the vaccination programme.

HPV vaccination has been shown in this study to reduce the chances of women getting pre-cancerous cells in the cervix, but we need to see longer-term results to be sure this translates into a reduced chance of cervical cancer.

Most young women aged 14 to 25 in the UK should now have received the vaccine, meaning rates of cervical cancer may drop in the coming decades. In the meantime, women should continue to attend screening appointments for cervical cancer when invited.

Find out more about the HPV vaccine.

Analysis by Bazian
Edited by NHS Website