Let’s not be in a hurry to remove the mask indoors. Let’s see how transmission evolves and how hospitalisations evolve. Especially after the withdrawal of the rest of the measures, including gauging, testing and isolation.
Salvador Peiró 29/3/2022 11:00 CEST
The risk of covid-19 transmission is much higher indoors than outdoors.
“Sooner rather than later”. This is the phrase most frequently used by representatives of the different health administrations when asked about the date for the withdrawal of the obligatory use of masks indoors. However, despite the fact that after two years of the pandemic there is a desire to do so, they avoid setting final dates.
They are right to do so. During this time we have also learned to be a little more cautious. Indoor masks have an important role to play in containing transmission and the current situation still leaves a lot of uncertainties. In any case, it is an important measure that requires some reflection.
Key issues before removing facemasks indoors
The risk of covid-19 transmission is much higher indoors than outdoors. Moreover, this risk is not homogeneous and varies depending on factors such as air renewal (natural or mechanical ventilation), capacity, activities carried out indoors (higher in places where people talk loudly or sing) or the time spent in such environments.
Facemasks are extremely effective in reducing the transmission of covid-19 indoors. The higher the filtering capacity and the better the fit, the greater the effectiveness.
Similarly, the danger is particularly high in some environments (collective centres where many people live together) and more worrying when they include people with a higher risk of developing severe covid (homes, health and social care centres).
In indoor spaces with large numbers of people (leisure and cultural venues, restaurants, places of worship, teachers, etc.) or where many people live together on a stable basis (residences, adult education centres, prisons, hostels, internment centres, etc.) there is a risk of super contagion events, which can significantly change the dynamics of transmission in one area, accelerating and spreading it to other areas.
Protection against infection
Transmission, and especially the risk of developing severe covid, is significantly reduced in immunised people. By vaccination, natural infection or both (hybrid immunity). This protection is greater in people who have received a booster dose.
This protection against infection, as it is much more durable against the development of severe disease, is reduced over time. It is also reduced with some variants (omicron) that have some ability to evade the defence offered by vaccines or by infection with other variants (again, referring to infection rather than the risk of severe covid).
Although everyone can develop the most severe form of the infection, the risk is much higher in some groups (elderly, immunocompromised, with some specific co-morbidities or unvaccinated who have not been previously infected).
Although several experts believe that masks may cause some problems (especially learning and social interaction problems in younger children), there are no quality studies that show health or social problem associated with their use.
If the transmission in the general population is high, it is very difficult to prevent it from permeating to vulnerable groups or settings. Neither in Spain, nor in neighbouring countries, and even using extreme isolation measures, has it been possible to avoid high mortality in homes for the elderly.
The mandatory use of masks indoors, which is undoubtedly uncomfortable, is not a particularly disruptive measure for the economy. Less so than capacity limits or other restrictions. And, although several experts believe that it may cause some problems (especially learning and social interaction problems in young children), there are no quality studies that show any health or social problems associated with its use.
The current situation in Spain
After an extraordinary 6th wave in terms of volume of infection and after a relatively rapid decline, transmission in Spain seems to be stagnating around 14-day cumulative incidence figures of over 400 reported cases per 100,000 inhabitants. These are high figures. Quite high. Moreover, with the current “testing” strategy, the actual number of cases will be much higher than those reported
With the new testing strategy, the difference between reported and actual cases will increase further and, in practice, case incidence will lose its (already limited) usefulness as a benchmark indicator for the adoption (or de-adoption) of covid-19 strategies.
The incidence of new cases (rather than the “bed occupancy rate”), hospitalisation and ICU admissions – with some distortion by not differentiating whether these are admissions “for” or “with” covid – have for many weeks now been the benchmark indicators to inform disease strategies. They also appear to be stagnating, albeit in numbers that should not prevent adequate care for covid and non-covid patients.
On the other hand, we do not have information on population adherence to indoor mask use (or compliance with isolations). It is likely to be high in some settings (schools, airports, public transport). It is just as likely to be very low in other settings. And the end-of-measures and end-of-mask announcements, which have been repeated so often in recent weeks, must not be helping to maintain adherence to their use.
Finally, we have a very high proportion of people with a full regimen and people with recall doses. These proportions are particularly high in older people, who are the ones who produce the most severe cases.
In addition, we have to reckon with a huge proportion of people – vaccinated or not – who have passed the infection during the 6th wave. Recorded cases approximate 25-30% of the population. But actual cases are likely to be double these figures.
Particularly relevant are the infection rates in unvaccinated adults. This relatively small population group has caused a disproportionate number of severe cases during the sixth wave and most of them are likely to have some protection from infection already. It is unlikely that they will again cause half of the covid admissions to ICUs.
So when do we remove the mask indoors?
In the most likely scenarios for the coming weeks – without the presence of new disruptive variants due to a high vaccine escape capacity – a certain upturn in the transmission is to be expected due to the actual reduction of restrictive measures (although due to the downward adjustment of the test the official data say otherwise).
But the population has significant protection against severe disease and this upturn should not translate into a significant increase in severe cases. This situation would allow, at least in theory, to suspend the mandatory use of masks indoors and also, as already announced, to bring the approach to covid closer to that of other upper respiratory tract infections, where testing or isolation is unusual.
But transmission figures are still very high. And highly variable. From communities with incidences of 900 per 100,000 to others with 200 per 100,000. From communities with clearly rising incidence to others still falling. And locally these variations are even greater. Some localities are even in a very complicated situation. Are the same measures going to be applied in places with extraordinarily different epidemiological realities?
How will transmission monitoring be operationalised when new – and welcome – changes in the epidemiological surveillance system are announced for next year? What measures can be taken to ensure that the most vulnerable populations are affected as little as possible by the upturns? How will the social communication of what is, in practice, a transfer of much of the responsibility for transmission to individual behaviours is carried out?
When the transmission is high, it is very difficult to prevent it from reaching old people’s homes (now 6 months after booster doses) and vulnerable groups. Although the proportion of severe covid cases is much lower now than before omicron and the third doses, rates like the current ones will still result in significant proportions of hospitalisations and deaths in these groups.
In short, let’ ‘s not be in a hurry to remove the mask indoors. Let’s see how transmission evolves and how hospitalisations evolve. Especially after the withdrawal of all other measures, including gauging, testing and isolation. Let’s put in place new transmission monitoring systems (e.g. regular sampling) and let’s continue to monitor residences. Let’s move forward, but let’s take it slow.
If transmission drops further, we could start with school children. Perhaps also in some settings (catering) where the use of masks is less than negligible. Other things may have to be left to the end (long-distance transport). Or different measures may have to be taken depending on the risk traffic lights that we use for so few things. Rather than introducing or removing measures, the reasonable thing to do might be to prepare a plan for a gradual withdrawal, by sectors, and provided that certain conditions are met.
Salvador Peiró is an epidemiologist and researcher in the Health Services and Pharmacoepidemiology Research Area of the Foundation for the Promotion of Health and Biomedical Research of the Valencian Community (FISABIO), Valencia.