Flawed reasoning: The claim implies that masks are ineffective or useless against COVID-19, otherwise non-mask wearers should be dead. However, protective equipment can be recommended or necessary even against diseases that are not systematically deadly. The claim also forgets to consider that the use of masks reduces the propagation of the virus among the population and thus indirectly limits the risk of exposure of non-mask wearers.
FULL CLAIM: If masks were effective and necessary, non-mask wearers should be dead by now
REVIEW
In August 2020, a post circulating on social media, which received millions of views, questioned how people who are not wearing face masks in the midst of the COVID-19 pandemic have still remained alive. Using the rhetorical technique of “just asking questions”, this claim suggests that masks are ineffective or useless against COVID-19. This reasoning is based on the premise that a protective device is only efficient and necessary if 100% of people not using it dies. Such logic is actually flawed and inconsistent with the available knowledge about the disease.
Firstly, it is easy to see that protective equipment can be useful even though not using it will not automatically result in someone’s death. For instance, not everybody who gets on a motorcycle without wearing a helmet dies, even though wearing such protection is effective and highly recommended.
Secondly, not everyone exposed to SARS-CoV-2 is bound to get infected. We can obtain an estimate of how infectious a virus is by looking at a parameter called the secondary attack rate. The secondary attack rate is the proportion of people who are infected after coming into contact with an infected person. Therefore, a 100% secondary attack rate means that everybody who interacts with an infected person would also be infected.
As we might expect, the secondary attack rate will vary depending on the type of interaction. For example, the household secondary attack rate, focusing on persons sharing the same household with the infected patient, tends to be higher than the secondary attack rate including all types of interaction. Muge Cevik, a researcher in infectious disease at the University of Saint Andrews, shared on Twitter several published estimates of secondary attack rates. While varying between studies, the reported secondary attack rates in households were roughly between 10 and 20% while the secondary attack rates considering all kinds of contacts were even lower.
An analysis of hundreds of COVID-19 cases in Shenzhen as well as their close contacts yielded a household secondary attack rate of 11.2%[1]. Similar analysis in Guangzhou gave a secondary attack rate of 17.1% among people sharing the same address as an infected person[2]. In a superspreading event in the US, a particularly high 53.3% secondary attack rate was calculated. These numbers mean that a person in contact with an infected patient will not necessarily get infected by the virus.
Thirdly, even when a person gets infected, death will not necessarily ensue. The infection fatality ratio (IFR) compares the number of deaths to the overall number of infections. Determining the IFR is not easy because not all the COVID-19 infections and COVID-19 related deaths are known in absence of systematic testing and autopsy. Furthermore, it is easy to see that the probability of dying highly depends on the demographics and the capacity and reactivity of the local health system. In addition, the IFR varies greatly among the population with the most vulnerable groups such as the elderly presenting a higher IFR. However, a team from the Pasteur Institute estimated the IFR in France to 0.5%[3], meaning that among 1000 infected persons, 5 patients died on average. The Centers for Disease Control and Prevention in the U.S. (CDC) recently updated their epidemiological predictions. Their best estimate provides an IFR for the U.S. of 0.65%. The CDC further estimates that 40% of infections remain asymptomatic.
Altogether, this shows that being exposed to SARS-CoV-2 does not give a 100% chance of getting infected, and getting infected does not always result in death. Therefore, it is well within expectations that most people who do not wear masks are still alive, and this cannot be used to make conclusions about the usefulness or efficiency of masks.
Furthermore, masks not only protect oneself from being infected but also limit the risks of infecting others. As a result, people with uncovered faces indirectly benefit from a reduced virus transmission due to others wearing masks, analogous to the herd immunity effect. Indeed, Health Feedback previously explained that currently available scientific data support the fact that wearing masks reduces the risk of SARS-CoV-2 propagation by decreasing respiratory droplets exhalation and inhalation. Analyzing the spread of COVID-19 in Wuhan, Italy and New York City, researchers found that face covering masks reduced the number of infections[4].
REFERENCES
- 1 – Bi et al. (2020) Epidemiology and transmission of COVID-19 in 391 cases and 1286 of their close contacts in Shenzhen, China: a retrospective cohort study. The Lancet Infectious Diseases.
- 2 – Jing et al. (2020) Household secondary attack rate of COVID-19 and associated determinants in Guangzhou, China: a retrospective cohort study. The Lancet Infectious Diseases.
- 3 – Salje et al. (2020) Estimating the burden of SARS-CoV-2 in France. Science.
- 4 – Zhang et al. (2020) Identifying airborne transmission as the dominant route for the spread of COVID-19. Proceedings of the National Academy of Sciences.
