The HPV vaccine and cervical screening: how many tests do you need?

It’s coming up on 10 years since the human papillomavirus (HPV) vaccine was first introduced in the UK as a way to curb a cancer-causing infection.

HPV is a common virus. Most adults have it at some point in their lives and the infection usually clears itself up without causing any problems. But for some types of HPV, not clearing the virus can lead to cervical cancer – in fact this is linked to all cases of the disease in the UK.

That’s why the vaccine, which protects against infection with certain forms of the virus, was introduced in 2008 and is routinely offered to girls aged 11-13.

In the next few years those from the first group to be vaccinated as part of the established vaccination programme will receive their first invitation to cervical screening. So a key question researchers have been asking is: can vaccinated women attend cervical screening less frequently?

Now, new research from Cancer Research UK-funded scientists at Queen Mary University of London (QMUL) estimates what the optimum number of screens might be.

The study, published in the International Journal of Cancer, suggests vaccinated women may only need 3 cervical screens in their entire life, rather than the 12 that are standard for all UK women today.

If I’ve been vaccinated, why might I need fewer screens?

Cervical screening looks for abnormal cells in the cervix that can develop into cancer.

This is done by taking a sample of cells, and sending them to a lab where they are tested to see if they are normal (cytology). Testing for HPV is carried out on abnormal cells, to see if they may be becoming cancerous. But soon the order of the tests will switch, and the cells will be tested for HPV infection first, and only those that have the virus will be examined for signs the cells aren’t normal.

This change to HPV primary testing will happen across England, Scotland and Wales by December 2019.

Both the HPV vaccine and cervical screening are intended to prevent cervical cancer. The vaccine works by preventing infections that cause about 70% of cervical cancers. Screening works by finding abnormal cells that sometimes develop into cancer and removing or destroying them.

– Professor Peter Sasieni, QMUL

“Both the HPV vaccine and cervical screening are intended to prevent cervical cancer,” says Professor Peter Sasieni, lead researcher on the latest study. “The vaccine works by preventing infections that cause about 70% of cervical cancers. Screening works by finding abnormal cells that sometimes develop into cancer and removing or destroying them.”

So if both the vaccine and the screening programme protect against cervical cancer, regularly checking for infection in vaccinated women could be overkill. Because these women are already protected by the vaccine, Sasieni believes that less frequent screening “is enough to prevent the vast majority of cervical cancers”.

In the latest study, Sasieni’s team used data to estimate what would happen if vaccinated women never received any screening, then tested what would happen in their computer model if different screening scenarios were introduced. They compared these numbers to predict the benefits of different frequencies of screening, this showed that a total of 3 screens at ages 30, 40 and 55 offered the same protective benefit as the 12 screens a woman can receive in the current programme.

The vaccine protects against infection with the 2 forms of the virus most strongly linked to cervical cancer, but there are many other types. This is why vaccinated women still benefit from screening – they are just likely to need less of it.

Research like this also addresses a key challenge for screening: how to get the best balance between protection and unnecessary procedures.

I haven’t been vaccinated. Do I still need to go for screening?

Women who haven’t had the vaccine don’t get the protection against HPV infection and so their risk of cervical cancer isn’t reduced. This means that they will need more screens over the course of their lives than vaccinated women to detect abnormal cells and protect against cervical cancer.

But this latest study suggests even these women could get equivalent protection from fewer screens once HPV testing is offered upfront in 2019. Once that change in testing happens, Sasieni’s team think 7 lifetime screens for unvaccinated women would be enough.

“Screening works,” he says, “women who go for regular screening are extremely unlikely to die from cervical cancer.”

“In the future, the HPV infection may become much less common in everyone, because vaccination will have stopped the spread of infection. But we are still a long way from that time.”

So in the meantime, make sure you’re registered with your GP to receive your screening invitation.

Questions that still need to be answered

This study takes lots of information about the protection from the vaccine and the effectiveness of screening to make mathematical predictions about how often a vaccinated woman might need to be screened. But this regularity of screening hasn’t been tested in real life.

The UK governments also haven’t yet made any decisions about changes to the screening programme to account for the protection the vaccine offers, or the impact changing to up-front HPV testing will have on how frequently women are invited.

So, for now, women aged 25-49 will still be invited every 3 years for screening, and every 5 years for those aged 50-64.

We need to think how we change a one-size-fits-all screening programme to a programme that is adapted to different needs

– Professor Peter Sasieni

There are still lots of questions about how to change the screening programme in real life to get the most benefit for everyone, without compromising the protection against cancer. “There is a challenge for the programme of how to adapt rapidly to take advantage of the latest innovation while ensuring that safety is maintained,” says Sasieni.

We now have two groups of women who need different amounts of screening. “We need to think how we change a one-size-fits-all screening programme to a programme that is adapted to different needs,” says Sasieni. This will come with some logistical challenges that need to be considered in any decisions about changes to the screening programme.

Sasieni adds that the screening programme needs to be able to “tailor screening to each woman’s needs”.

We also don’t know how being invited less often might affect the likelihood a woman attends screening at all. If you only get an invitation every 10-15 years, would that make you more or less likely to go? And because women might hypothetically only be attending 3 screens in their lifetime, missing one could have a big impact.

So, is this good news or bad news?

While there are still lots of details to be ironed out, the findings of this study are great news for women. They also point to potential benefits for the NHS too, as resources could be saved through less screening.

The bottom line is all women can receive protection from cervical cancer, either through the screening programme alone, or in combination with HPV vaccination. So if you’ve been vaccinated or not, it’s still important to go for screening.

There’s also the distant goal of screening no longer being necessary, because HPV vaccination makes the risk of being infected so low. This study points to the benefits that vaccination could bring, but some flexibility in the screening programme will be needed soon to help get the maximum benefit for women.

Sophia Lowes is a health information officer at Cancer Research UK