Do I have to wear a mask if I don't have any symptoms?
Text updated on 2020-09-20
Yes, because you can be contagious even without symptoms. I'm wearing a mask to block the SARS-CoV-2 virus!
Yes. Even if a person has no symptoms, they can be infected with the SARS-CoV-2 coronavirus and be contagious. That person may be asymptomatic, which means they may have COVID-19 but no symptoms, or pre-symptomatic (have COVID-19 but not yet symptoms), or post-symptomatic: (previously had COVID-19 and no longer have any symptoms). In all three cases, the person may exhale viral particles that can infect others. Epidemiological studies have shown that about half of all infections are caused by people who do not have symptoms.
Putting on your mask is a civic act: together, we reduce the spread of the virus and the contamination of vulnerable people.
The mask reduces the amount of seasonal human coronavirus and influenza viruses in expired droplets and aerosols.Leung, N.H.L., Chu, D.K.W., Shiu, E.Y.C. et al. Respiratory virus shedding in exhaled breath and efficacy of face masks. Nat Med (2020).
Five people were infected by an asymptomatic carrier.Bai, Y., Yao, L., Wei, T., Tian, F., Jin, D. Y., Chen, L., & Wang, M. (2020). Presumed asymptomatic carrier transmission of COVID-19. Jama.
Cases of transmission by pre-symptomatic carriers.Wei, W. E., Li, Z., Chiew, C. J., Yong, S. E., Toh, M. P., & Lee, V. J. (2020). Presymptomatic Transmission of SARS-CoV-2-Singapore, January 23-March 16, 2020. Morbidity and Mortality Weekly Report, 69(14), 411.
The viral load in asymptomatic patients is similar to that in symptomatic patients.Zou, L., Ruan, F., Huang, M., Liang, L., Huang, H., Hong, Z., ... & Guo, Q. (2020). SARS-CoV-2 viral load in upper respiratory specimens of infected patients. New England Journal of Medicine, 382(12), 1177-1179.
A pre-symptomatic person infected two people following a business meeting that lasted more than a day. One of the contaminated individuals then contaminated two other colleagues following 2 (and 4) brief contacts at the workplace when she was not yet symptomatic.Rothe, C., Schunk, M., Sothmann, P., Pretzel, G., Froeschl, G., Wallrauch, C., ... & Seilmaier, M. (2020). Transmission of 2019-nCoV infection from an asymptomatic contact in Germany. New England Journal of Medicine, 382(10), 970-971.
By measuring viral shedding in 94 patients with an infectivity profile, COVID-19 was confirmed in the laboratory, and by analyzing 77 contaminant-contaminated transmission pairs, it was estimated that 44% (95% confidence interval, 30-57%) of the infections occurred during the presymptomatic stage.He, X., Lau, E. H., Wu, P., Deng, X., Wang, J., Hao, X., ... & Mo, X. (2020). Temporal dynamics in viral shedding and transmissibility of COVID-19. Nature medicine, 26(5), 672-675.
In this modeling study, it is considered that cases of SARS-CoV-2 contamination originate in 46% of cases from presymptomatic (before presenting symptoms) persons, in 38% of cases from symptomatic persons, in 10% of cases from asymptomatic persons (who never present symptoms) and in 6% of cases from indirect transmission via the environment. Estimates for the last two routes are speculative.Ferretti, L., Wymant, C., Kendall, M., Zhao, L., Nurtay, A., Abeler-Dörner, L., ... & Fraser, C. (2020). Quantifying SARS-CoV-2 transmission suggests epidemic control with digital contact tracing. Science, 368(6491).