Studies on the effectiveness of using a mask during the pandemic have very variable and unreliable results. There is even less information about its effectiveness in the case of flu.
With the early arrival of flu season and recommendations from NHS (United Kingdom National Health Service) authorities that people with symptoms wear masks in public, the question arises: will Do masks really work against the flu?
The short answer is that the evidence are still surprisingly weak. Studies carried out before the COVID-19 pandemic generally found that masks made little or no difference to the spread of influenza in everyday settings. There is little reason to believe this has changed, although the COVID-19 pandemic has taught us more about when masks can be useful in reducing the spread of respiratory illnesses.
This is important because flu cases started to increase earlier than usual this year and are higher than expected for this time of year.
Although the number of people hospitalized with a diagnosis of influenza is still at moderate levels, the number of daily hospitalizations is increasing. There are real concerns that we are heading for a particularly harsh winter. This year, the Australia suffered its worst flu season in at least 20 years.
The main strain of flu currently circulating in the UK is a type of flu A known as H3N2 – subclade K. This strain probably first emerged in the US, from where it spread globally, prolonging the flu season in Australia and New Zealand and causing an early start to the flu season in Europe.
Crucially, this strain is quite different from the one used in the vaccine this year. This means the vaccine may be less effective at preventing infection, although it should still help protect against serious illness.
In this context, Daniel Elkeles, chief executive of NHS Providers, told Times Radio that if you are coughing and sneezing, “you should wear a mask when in public spacesincluding on public transport, to reduce the chances of transmitting the virus to other people”.
Government guidance is less direct, with a spokesperson saying that people should consider wearing a mask in these circumstances, not that they have to wear one.
Before the COVID-19 pandemic, several studies had already investigated the benefits of using face masks against respiratory viruses, including the flu. The most thorough review concluded that, overall, masks made little or no difference in the spread of influenza, both at home and in public places.
They also concluded that N95 masks (high filtration, tight-fitting masks) were no better than surgical masks in everyday situations. However, the authors were only able to identify a single low-quality study to support this conclusion.
A review of the effectiveness of masks in spreading respiratory infections before COVID-19 found a similar, weak overall effect. But the individual studies in the review often had very different results from each other.
Lower quality studies were more likely to suggest that masks worked
Some studies have suggested a strong protective effectwhile others showed a greater risk of infection when people wore masks. Better quality studies, such as randomized trials, have generally found little or no benefit. In contrast, lower-quality studies were more likely to suggest that masks worked.
The COVID-19 pandemic has added new evidence. The most recent robust review of masks and COVID-19 in the community concluded that mask use was associated with a reduced risk of COVID-19 transmission outside of healthcare settings. There was insufficient evidence to comment on the relative effectiveness of N95 respirator masks compared to standard surgical masks in public spaces, but in hospitals, the body of evidence indicated little difference between the two mask types.
These real-world studies are in stark contrast to laboratory studies, which have generally found masks to be highly effective at reducing the amount of virus released by people into the air and have demonstrated that N95 masks, when properly fitted, are more effective than surgical masks for COVID and flu.
In the flu study, researchers reported that a well-fitting N95 mask reduced the amount of flu virus released into the air by more than 94%. However, a poorly fitted N95 mask did not perform better than a standard surgical mask – a crucial finding that suggests that the discrepancy between laboratory and real-world effectiveness may be related to How people actually wear masks.
The COVID lesson
Some of the most compelling evidence of the effectiveness of masks in preventing COVID came from the UK Office for National Statistics (ONS) COVID infection survey. In this study, up to 150,000 people were tested every two weeks for the virus, regardless of whether they had symptoms or not. During part of the period, the study also collected data on the use of masks.
An analysis of data from the ONS study concluded that, in adults, the constant use of a mask at work or in closed spaces – or both – was associated with a approximately 20% reduction in the risk of contracting COVID-19 during the period when the delta variant was the dominant strain of the virus.
But after the appearance of the omicron variant, there was little or no reduction in risk for those wearing a mask.
In children, mask use was associated with a lower risk reduction of testing positive for COVID-19 and, during the omicron variant period, there was even a small increase in risk.
The evidence on the effectiveness of flu masks is even less clear, suggesting little or no benefit. Even so, they should still be encouraged for people at risk of developing serious illness in closed, crowded environments – especially if they have not yet been vaccinated.
If someone has the flu, the It’s better to stay at home. If you need to go out into closed and crowded environments, you should also wear a mask. Mask use should not be encouraged in children, given the lack of clear benefits and the potential for inappropriate use.
For most people, the general evidence do not support the routine use of masks. It also makes no sense for the general public to wear N95 masks, as these masks need to be well-fitting to be effective. However, wearing a mask is a personal decision, and people should have the freedom to decide what makes them feel most comfortable.
