Do facemasks limit the contamination/spread of respiratory viruses?
To limit the spread of respiratory diseases, facemasks can be used by:
– healthy people, avoiding thus contamination by infected individuals
– infected people, limiting the spread of viruses to susceptible individuals
The use of masks is intuitively logical, as it provides a barrier, preventing the spread of droplets or aerosol containing viral particles. In fact, studies have shown that surgical masks or respirators are able to retain a large part of the viruses expelled by infected people. Under ideal conditions, which include the periodic replacement of surgical masks and receiving training for proper aseptic techniques, masks can be effective in partially containing the transmission of infectious agents. However, in the real world, where regular people without specific training must in addition to acquiring an arsenal of surgical masks, remember to thoroughly wash their hands before wearing a mask, not touching the mask with their hands, not removing it to have a cup of coffee or enjoy a meal and then put them back on (these masks must be removed and replaced with new ones), the efficiency of the masks drops tremendously.
The effectiveness of the use of masks as a tool to prevent the spread of respiratory diseases among regular people (unlike health workers, who receive specific training and have many masks at their disposal) has been tested in several “clinical trials”. Such experiments have been carried out over the past 15 years, some better conducted than others. A recent study, published in 2020, compiled the results obtained in the best randomized clinical trials (RCTs) on this topic (MacIntyre and Chughtai 2020). Randomized means that the individuals who participated in these studies were divided into subgroups, made up of masked and unmasked (control group) at random, but balanced in relation to general health condition, sex etc. RCTs are the golden standard of clinical trials. There are several observational (cohort) studies about mask efficacy, but we are not going to cover them. In contrast to RCTs, observational studies are not randomized. In these type of study, we observe differences in outcomes that occur after treatment decisions have been made without ensuring that patients in different treatment arms have similar unbiased characteristics. Hierarchically speaking, RCTs are more reliable than observational studies.
In addition, it should be said that in the biomedical sciences, studies that report negative results are less likely to be published than those with positive results. Given the considerable high investment made in RCTs (they are more difficult to design and are more expensive), even RCTs with negative results are more likely to be published than their observational counterparts.
Seven RCTS have been carried out in which healthy individuals in the community wore masks and another 3 studies in which a mask was worn by infected individuals. Each of these studies typically involved many tens or even hundreds of people.
It should be noted that in all of these studies, the use of masks took place in the context of closed places, be they households, student housing or hospitals. In none of these cases the use of masks in public and open places has been tested. There is a good reason for this, as we will see later on. Some of these studies tested the efficacy of masks only, others tested the efficacy of masks + hygiene measures, such as frequent hand washing.
In order to conclude on the efficacy of masks as able to prevent the spread of respiratory viruses, there must be a significantly lower number of secondary infections (people who contract the virus from an infected household member) in the masked group than in the control group.
In most studies in which masks were used by healthy people with the intention of protecting them, susceptible individuals, by means of a mask, no statistically significant protective effect was observed (5 out of 7 studies). That is, in these studies there was no clear difference between the masked group and the control group. In two studies, a small statistically significant difference was observed. In one of those (Cowling et al. 2009), there were 3 groups: the control group, the hands hygiene group and the hands hygiene + mask group. The hands hygiene group displayed an odds ratio of 0.46 compared to the control group. This means that the chance of those wearing masks getting contaminated was 0.46 times lower than that of the control group. In other words, the chance of the unmasked group to contract the disease was 1/0.46 = 2.17 times higher. The hand hygiene + masks group showed an odds ratio of 0.33, that is, mask wearing decreased the risk by 0.13. Therefore, the chance of the hands hygiene + mask group for becoming sick was 3 times lower than that of the control group, while the chance of the hands hygiene group (without masks) to get infected was 2.17 times less than that of the group control. Clearly, the greatest benefit was frequent hand washing, while mask wearing conferred a secondary contribution. Furthermore, according to this study, both interventions had a positive effect if they were applied by the susceptible individuals within the first 36 hours from the onset of symptoms of the infected individuals with who they were in contact.
Of the 7 studies mentioned above, this is the one that had the most statistically significant results regarding the use of masks. The other studies displayed either negative results, or positive outcomes but without statistical significance or other limitations. To see the references cited in this article and a summary of their results can be found here.
A common, and to some extent correct claim is that facemasks should be worn by everyone in order to prevent infected individuals (symptomatic, pre-symptomatic or asymptomatic) from contaminating susceptible individuals. Three studies were carried out that tested this possibility. One of these studies took place in France (Canini et al. 2010), involving 105 infected people. The authors of this paper concluded that there was no difference between the control group and the group in which infected people wore masks. In another study carried out in Saudi Arabia (Barasheed et al. 2014), during the annual Islamic pilgrimage, it was found that the group that wore masks infected 31% of the people accommodated in the same tent, while in the control tent, where the infected did not wear masks, that number rose to 53%. However, these data were based on reports from the study participants who reported their own symptoms. When the sick participants were tested for the presence of 5 types of viruses that could potentially cause these symptoms, the difference between the groups disappeared. Thus, the symptoms reported by the study participants could have been caused by other factors, other than the viruses supposedly spread by the infected individuals (with or without masks).
Finally, in a study conducted in China (MacIntyre et al. 2016), 245 infected patients were divided into 2 groups, with and without facemasks. The number of residents in the same household who contracted the disease was assessed either by symptoms reporting or laboratory testing. Infection rates measured by symptom reports showed a downward trend, but not statistically significant when the facemasks and control groups were compared. However, the advantage of the masked group was eliminated when the sick individuals were submitted to laboratory tests to detect the presence of viruses. In this case, there was no difference between the groups.
Two caveats must be stressed:
1- All studies mentioned above involved tests in which individuals wore surgical masks or respirators. None of them used cloth masks. There is a single RCT that tested the effectiveness of cloth masks in a hospital setting – (MacIntyre et al. 2015). Their conclusion is that these masks should NOT be used in these environments. The group of healthcare workers who wore cloth masks had a higher risk of contracting respiratory diseases than the control group that did not wear any masks. ADDENDUM: A new paper (published on 7/21/2020 and not yet peer-reviewed) showed that cloth masks were completely inefficient in containing SARS-CoV-2 particles (Loupa et al. 2020).
2- No study has tested the use of masks in open spaces to limit the spread of respiratory diseases in the outdoors. The reason for this is simple: the use of masks in open spaces is unnecessary and defies the laws of microbiology. Viruses released by an individual in an open environment either in the form of aerosol or small droplets are immediately diluted, considerably reducing what virologists call “infectious dose” (the number of viruses required to infect a healthy person). Microbiologists working with viruses know that one of the most efficient ways to stop a viral infection is to dilute the viruses and host cells, which is a good analogy to what happens in a dynamic open space – viruses spread (dilute) in the air as people walk by. In addition, in the presence of solar radiation, RNA viruses such as SARS-Cov-2 are inactivated in a matter of tens of minutes (Lytle and Sagripanti 2005). In other words, for a person to be infected by viruses expelled by others in an open environment, there must be a great proximity between them. Unless the infected person sneezes or coughs directly into the susceptible individual’s face, the risk of becoming infected outdoors is very low.
In conclusion, there is little reliable evidence that wearing masks, either by healthy people or by infected individuals, has any consistent benefit in preventing respiratory disease. The authorities should take these scientific data into account before decreeing the mandatory use of masks in public spaces. The use of masks in open places, where there is no agglomeration (minimum distance of 1 meter between people), as in streets, parks and beaches, defies basic laws of microbiology. In confined places such as buses, subways and markets, mask wearing may be recommended, but given the low level of evidence regarding mask protection, it should not be mandated.
Lastly, I would like to draw a parallel between traditional vaccines and masks. Vaccination is certainly the medical invention that saved most lives in history. Vaccination is so efficient and powerful that it has eradicated a terrible disease like smallpox. Vaccination also prevents super-contagious diseases such as measles and has been able to decrease the number of children affected by Polio to zero in Western countries.
However, the vast majority of the population should be vaccinated in order to achieve full protective capability. In the case of measles, “collective immunity”, also known as “herd immunity” is attained only when 93-95% of the population is vaccinated.
Despite the enormous benefits of vaccination, there is no punishment for parents who refuse to vaccinate their children. The worst that can happen is that one or the other school would refuse to enroll unvaccinated children. No fines, imprisonment or any other coercive measure.
So how is that facemasks, whose efficiency is at best controversial became mandatory in some countries under penalty of fine or prison, while vaccination, which definitely works and effectively protects our children (and adults too) is only optional?
UPDATE (19.11.20)
A Danish RCT with 6000 participants (4862 completed the study) with roughly 3000 in each test and control arms have found NO statistically significant effect of masks wearing by the general population on the transmission of Covid-19 (Bundgaard et al. 2020). This is the largest ever published study on the subject of masks prevention of respiratory diseases.
The trend continues: the better the study, the smaller the effect of masks of virus transmission.
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