A study published a few days ago in the journal BMJ Global Health concludes that the use of masks at home is effective and recommended to stop the spread of COVID-19. However, the success of this prevention measure would depend on the moment in which the use of the masks begins: they must be worn before the infected person begins to manifest symptoms of COVID-19. Other protection measures such as frequently cleaning the house with a disinfectant are as effective, around 77%.
Avoiding crowds and maintaining physical distancing measures, as well as the use of masks in public transport and other places where it is not possible to maintain this distance, have been shown to be effective measures to stop the transmission of the virus. However, it is not entirely clear whether wearing a mask indoors is equally effective. To verify this, the researchers called 460 people from 124 families in Beijing who had lived with someone infected with SARS-CoV-2 and asked them about their lifestyle habits during the pandemic. The results revealed that in 41 of the 124 families the virus had been transmitted between several of its members, making a total of 77 infected adults and children. Families who used to clean their homes with disinfectant daily, who ventilated and who kept a distance of one meter were less likely to transmit the virus, even in larger families.
Should authorities recommend the use of masks at home?
“The results of the study are not robust, it has several limitations both in the design and in the statistical analysis,” explains Antonio Lazzarino, researcher in the Department of Epidemiology and Public Health at the Global University of London, to Science Media Center . “The main limitation is that it is designed at the family level and not at the individual level. This means that the authors have not considered the individual risk of becoming infected with or without masks: what they did was to evaluate whether families with a habit of wearing a mask had a greater or lesser risk of contracting COVID-19 ”. That is to say: surely the families that use the mask at home are also less likely to be infected for other reasons that have nothing to do with it. For example, it is likely that they are people who keep physical distance with more discipline on the street, or who have confined themselves before to avoid being infected.
“In addition, it is a retrospective study based on a questionnaire, so it can potentially be affected by recall bias,” adds Lazzarino. “The type of mask used is not distinguished either, whether it was surgical, cloth … Ultimately, this work alone would not be enough to make recommendations of any kind .”
For Babak Javid, a researcher at the Tsinghua University School of Medicine (Beijing), however, the study yields some interesting data: “We still do not know with certainty the transmission routes for COVID-19. This work highlights a number of factors: first, that most transmission occurs before patients show symptoms. Waiting for people to develop symptoms will not help to break the chain of transmission ”, reflects the expert. “Second, there is a current debate about whether the transmission is by aerosol. These data suggest that this would not be the case, since the isolation of the primary case within the home by simple physical distancing was associated with a substantial decrease in the risk of transmission. Third, the use of masks, even within homes, can reduce transmission, but only if used before the primary case shows symptoms. This has obvious pragmatic implications, and this measure would be difficult to apply, but suggests that masks are more useful in preventing transmission from presymptomatic individuals. Finally, the use of detergents and disinfectants also had a protective effect : this suggests that some transmission of COVID-19 is due to contamination of surfaces and, again, has far-reaching implications at the public health level ”.
