Have face masks become less effective at managing COVID?

With fresh concerns surrounding rising flu, Strep A and COVID Omicron sub-variant XBB.1.5 cases, health officials across the UK are scratching their heads over one key question: should we all be wearing masks again?

While the UK Health Security Agency (UKHSA) has advised adults who are displaying symptoms of flu or COVID to wear a face covering, some public figures have advised all healthy adults to wear a mask in certain settings. For instance, in a briefing on 9 January, Scottish First Minister Nicola Sturgeon stated: “We continue to advise those over the age of 12 should wear face coverings when on public transport or in public indoor spaces.”

However, as COVID begins to stabilise in the UK, some scientists have questioned how effective face masks are at controlling current case numbers.

“Masks were really helpful early in the pandemic. And for people to argue that masks weren't is seriously wrong," Prof Paul Hunter from the Norwich Medical School of the University of East Anglia tells BBC Science Focus.

"But there is evidence that masks were an essential part of our control measures up until the point that we’d effectively vaccinated as many people as we were going to. What we’ve seen this year is that their protection has evaporated.”

Where's the evidence for this? Primarily, the claim hinges on data collected by the Office of National Statistics (ONS) between November 2021 and May 2022 that monitored how likely people who did and didn’t wear a face mask would test positive for COVID.

These figures indicate that throughout the end of 2021, children and adults who declared they “always” wore a face covering at work or school were less likely to test positive for COVID-19 compared to those who “never” or “sometimes” wore a mask. As you may expect. However, from January to May 2022, this trend faded. The likelihood that somebody who never or sometimes wore a mask would test positive was extremely similar to the chance a person who always wears a face mask would test positive.

In other words, from January to May 2022, the risk of getting a COVID infection was nearly the same for those who did and didn’t wear a mask. And it’s from these data that scientists like Hunter have suggested factors other than face masks, like the population’s immunity levels, play a bigger role in determining levels of COVID in the population.

Does everyone agree with this finding?

No, scientists aren't all in agreement. Some have said there isn’t enough data, highlighting how the ONS figures on mask-wearing were last collected in May 2022 – eight months ago.

This means, they say, the study can’t reveal too much about today’s circumstances, particularly as the virus has mutated significantly over this period, with the emergence of new Omicron sub-variants.

“You can draw a general conclusion from these data. But I think an informed conclusion would be unwise because of the complexity of the situation. The virus has changed quite substantially over that period – we’re not looking at the same one through the pandemic,” explains Hugh Pennington, emeritus professor at The University of Aberdeen’s School of Medicine, Medical Sciences and Nutrition.

Then there’s the question of how accurately the data actually reflect people’s mask-wearing behaviour. For instance, there's no way of being certain if the survey participants wore a mask as much as they told the ONS. While these issues are inevitable with this kind of study, some still think such flaws are significant enough to suggest that masks may still be effective.

As Pennington says: “The data is certainly very interesting, but it’s actually quite difficult to interpret and confirm because you can't do controlled trials. You can’t, for instance, infect somebody with the virus and put them in a room with people who are and aren’t wearing masks and see what happens. The ONS data is quite broad brush, let’s put it like that.”

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The ONS themselves say that different variables can affect behaviours and the likelihood of testing positive for COVID – factors which aren’t represented in the data. For instance, the data doesn’t reveal if somebody’s workplace asked them to wear a mask in response to an outbreak. The survey also doesn’t record if participants have jobs that may expose them to more COVID than usual.

An ONS spokesperson told BBC Science Focus:“These figures also come after the compulsory face mask wearing and other measures were relaxed, which may also impact our statistics.

“At the moment, we no longer produce the model that generates the statistics in question. In May 2022 we undertook a review and decided to pause the use of this model. However, we continually review our output and we may resume publication should it be needed.”

But why would wearing face masks not be as effective at controlling case numbers?

It’s a good question. After all, the material and structural integrity of the masks haven’t changed. So what’s going on?

According to Hunter, while non-pharmaceutical interventions – think mask-wearing and school closures – had a large impact at the start of the pandemic, their effect has lessened as the outbreak approaches a point called endemic equilibrium. This is where case numbers remain at a relatively low and constant level, with most people being infected with the virus at least once previously and receiving at least one COVID vaccine shot.

“Case numbers will fluctuate slightly over time, but then settle to this equilibrium,” Hunter explains. “We’re at the point where the number of infections in the population is actually driven by how rapidly we're losing immunity from either the vaccine or previous infections, not by what we're doing to protect ourselves against the virus."

He adds: “As more and more people get the infection and recover, the risk changes. Many of the people you may infect are immune, so they don’t actually get infected.”

Another big change in the spread of COVID since the pandemic's beginning: the SARS-CoV-2 virus itself. Hunter theorises the emergence of the highly-transmissible Omicron variant also negates the protection offered by face masks.

“Omicron is so infectious that it will spread no matter what we do,” he says. “The reduction in transmission that you get with mask-wearing isn't going to be enough.”

Earlier in the pandemic, studies indicated that wearing a face covering can, given the correct material and fit, reduce the wearer’s chance of a COVID infection. However, as the protection is limited, epidemiologists like Hunter argue that face masks effectively only delay infection – particularly with the Omicron variant now in general circulation.

As Keith Neal, emeritus professor in the epidemiology of infectious diseases at the University of Nottingham, explains: “The key issue is that COVID is going to be around for years. And the best defence is vaccination and prior infection to some degree. If everyone wore masks, the rate of COVID infections would probably fall slightly. But eventually everyone is going to keep on catching it, depending on who they meet.”

Some research has also demonstrated how masks may only delay inevitable infections. For instance, this conclusion was reached in a US study that explored the probability children would seek care for COVID, comparing schools with and without mask mandates across 1832 counties. Initially, schools with mask mandates were less likely to seek care for COVID, but the difference in numbers between the two groups disappeared in a few weeks.

Hunter says: “I think – and this is a theory – that children who have never worn masks in schools are more likely to have had an infection earlier on. So by now, they are more likely to be a lot more immune than children who have always worn masks. At this point, the extra immunity balances out reduced exposure.

“And if you’ve been religiously wearing a mask, you are less likely to have had COVID by now. You are less likely, therefore, to have got what’s called hybrid immunity – immunity from a previous infection and vaccine. That is the best immunity you can have.”

Neal also points to how the benefits of community mixing may outweigh the need for face masks: “Early in the pandemic, while we were waiting for vaccines, masks were needed to flatten the curve and stop the use of the NHS Nightingale hospitals. Now, the benefits of social mixing and mental health should be considered.

“Take Strep A and IGAS. We don’t know why it’s spread so much, but it’s been suggested that people’s immunity has been weakened due to a lack of mixing. The benefits of masks to the community are much less than it was because COVID is less of a threat.”

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While he views infection as largely inevitable, Hunter does recommend that some groups should still wear a face covering in public.

“If I was much older or had a health condition that put me at risk, I would continue to wear a mask because it may reduce the chance that I get infected. And there is also evidence that if you're wearing a face mask and you still get infected, you get less sick," he says.

“The reasons why aren’t clear. But it could be because you may get a lower dose of the virus if exposed to it and you're wearing a mask – and the higher the dose, generally the more sick you become.

He adds: “I think face masks continue to have an important role. I just don't think the evidence supports mask mandates as being effective. But it’s still important for certain people, particularly the vulnerable, to continue wearing face masks.”

However, other scientists argue that all adults should wear masks in certain settings to protect themselves and others.

“I think the public health advice has to be in favour of masks,” says Prof Christopher Dye, epidemiologist and public health expert at the University of Oxford, and former director of strategy at the World Health Organisation (WHO). “You really don’t want to get infected so you can protect yourself from future infections. Even now it’s not a good idea to get COVID.

“There’s a risk it doesn’t get easier with later infections. You can get it three times and the third time could be the time you get a really nasty infection with unpleasant consequences. There are millions of people with extensive and extended symptoms from this virus.

“There’s no real need to wear a mask in an open high street, but in enclosed, high-risk settings, it is simply sensible.”

He adds: "I think the way to maintain immunity is through vaccine development and vaccine immunity. And I still don’t think gaining immunity through natural infection as a deliberate strategy is a good idea. Those most at risk are vulnerable and older people. And we need to look after them."

Doubtlessly, there is a debate on the benefits of wearing a face mask in public indoor settings if you don’t have flu or COVID symptoms yourself. But most scientists do suggest wearing a mask in indoor public settings if you are displaying symptoms, as per UK Health Security Agency (UKHSA) guidance.

“It's really just very straightforward. It’s got nothing to do with going back to lockdown rules. It's purely risk reduction – like how you don’t sneeze directly into somebody's face when they're looking at you. If you’ve got respiratory symptoms and you have to go out, wearing a mask is a public service!” says Pennington.