A Policy Perspective

The governments’ responses to the COVID pandemic have so far differed significantly worldwide. Swift actions to the initial outbreak were undertaken in China, as reflected by nearly simultaneous implementation of various aggressive mitigation measures. On the other hand, the response to the pandemic was generally slow in the western world, and implementation of the intervention measures occurred only consecutively. Clearly, the responsiveness of the mitigation measures governed the evolution, scope, and magnitude of the pandemic globally (Figs. 1 and 2).

Curbing the COVID-19 relies not only on decisive and sweeping actions but also, critically, on the scientific understanding of the virus transmission routes, which determines the effectiveness of the mitigation measures (Fig. 5). In the United States, social distancing and stay-at-home measures, in conjunction with hand sanitizing (Fig. 5, path a), were implemented during the early stage of the pandemic (March 16) (20). These measures minimized short-range contact transmission but did not prevent long-range airborne transmission, responsible for the inefficient containing of the pandemic in the United States (Figs. 1 and 3). Mandated face covering, such as those implemented in China, Italy, and NYC, effectively prevented airborne transmission by blocking atomization and inhalation of virus-bearing aerosols and contact transmission by blocking viral shedding of droplets. While the combined face-covering and social distancing measures offered dual protection against the virus transmission routes, the timing and sequence in implementing the measures also exhibited distinct outcomes during the pandemic. For example, social distancing measures, including city lockdown and stay-at-home orders, were implemented well before face covering was mandated in Italy and NYC (Fig. 5, path b), and this sequence left an extended window (28 d in Italy and 32 d in NYC) for largely uninterrupted airborne transmission to spread the disease (Figs. 2 and 3).

The simultaneous implementation of face covering and social distancing (Fig. 5, path c), such as that undertaken in China, was most optimal, and this configuration, in conjunction with extensive testing and contact tracing, was responsible for the curve flattening in China (Fig. 1). Also, there likely existed remnants of virus transmission after the implementation of regulatory measures, because of circumstances when the measures were not practical or were disobeyed and/or imperfection of the measures. Such limitations, which have been emphasized by the WHO (1), spurred on controversial views on the validity of wearing face masks to prevent the virus transmission during the pandemic (30). However, it is implausible that the limitations of mitigation measures alone contributed dominantly to the global pandemic trend, as exemplified by the success in China. Our work suggests that the failure in containing the propagation of COVID-19 pandemic worldwide is largely attributed to the unrecognized importance of airborne virus transmission (1, 20).

Mitigation paradigm. Scenarios of virus transmission under the distancing/quarantine/isolation measure only (path a), the measures with distancing/quarantine/isolation followed by face covering (path b), and the measures with simultaneous face covering and distancing/quarantine/isolation (path c). The short-dashed arrows label possible remnants of virus transmission due to circumstances when the measure is not possible or disobeyed and/or imperfection of the measure.

Conclusions

The inadequate knowledge on virus transmission has inevitably hindered development of effective mitigation policies and resulted in unstoppable propagation of the COVID-19 pandemic (Figs. 1–3). In this work, we show that airborne transmission, particularly via nascent aerosols from human atomization, is highly virulent and represents the dominant route for the transmission of this disease. However, the importance of airborne transmission has not been considered in establishment of mitigation measures by government authorities (1, 20). Specifically, while the WHO and the US Centers for Disease Control and Prevention (CDC) have emphasized the prevention of contact transmission, both WHO and CDC have largely ignored the importance of the airborne transmission route (1, 20).

The current mitigation measures, such as social distancing, quarantine, and isolation implemented in the United States, are insufficient by themselves in protecting the public. Our analysis reveals that the difference with and without mandated face covering represents the determinant in shaping the trends of the pandemic worldwide. We conclude that wearing of face masks in public corresponds to the most effective means to prevent interhuman transmission, and this inexpensive practice, in conjunction with extensive testing, quarantine, and contact tracking, poses the most probable fighting opportunity to stop the COVID-19 pandemic, prior to the development of a vaccine.

It is also important to emphasize that sound science should be effectively communicated to policy makers and should constitute the prime foundation in decision-making amid this pandemic. Implementing policies without a scientific basis could lead to catastrophic consequences, particularly in light of attempts to reopen the economy in many countries. Clearly, integration between science and policy is crucial to formulation of effective emergency responses by policy makers and preparedness by the public for the current and future public health pandemics.

References

1. ↵

2. World Health Organization

, Coronavirus disease (COVID-2019) situation reports. https://www.who.int/emergencies/diseases/novel-coronavirus-2019/situation-reports/. Accessed 9 May 2020. Google Scholar

1. ↵

2. A. R. Fehr,

3. S. Perlman

, Coronaviruses: An overview of their replication and pathogenesis. Methods Mol. Biol. 1282, 1–23 (2015). CrossRefPubMedGoogle Scholar

1. ↵

2. J. S. Kutter,

3. M. I. Spronken,

4. P. L. Fraaij,

5. R. A. Fouchier,

6. S. Herfst

, Transmission routes of respiratory viruses among humans. Curr. Opin. Virol. 28, 142–151 (2018). CrossRefGoogle Scholar

1. ↵

2. J. W. Tang et al.

, Airflow dynamics of human jets: Sneezing and breathing - potential sources of infectious aerosols. PLoS One 8, e59970 (2013). Google Scholar

1. ↵

2. N. H. L. Leung et al.

, Respiratory virus shedding in exhaled breath and efficacy of face masks. Nat. Med. 26, 676–680 (2020). CrossRefPubMedGoogle Scholar

1. ↵

2. V. Stadnytskyi,

3. C. E. Bax,

4. A. Bax,

5. P. Anfinrud

, The airborne lifetime of small speech droplets and their potential importance in SARS-CoV-2 transmission. Proc. Natl. Acad. Sci. U.S.A., doi:10.1073/pnas.2006874117 (2020). Abstract/FREE Full TextGoogle Scholar

1. ↵

2. R. Zhang et al.

, Formation of urban fine particulate matter. Chem. Rev. 115, 3803–3855 (2015). CrossRefPubMedGoogle Scholar

1. ↵

2. R. Tellier

, Aerosol transmission of influenza A virus: A review of new studies. J. R. Soc. Interface 6 (suppl. 6), S783–S790 (2009). CrossRefPubMedGoogle Scholar

1. ↵

2. O. V. Pyankov,

3. S. A. Bodnev,

4. O. G. Pyankova,

5. I. E. Agranovski

, Survival of aerosolized coronavirus in the ambient air. J. Aerosol Sci. 115, 158–163 (2018). Google Scholar

1. ↵

2. M. Richard,

3. R. A. M. Fouchier

, Influenza A virus transmission via respiratory aerosols or droplets as it relates to pandemic potential. FEMS Microbiol. Rev. 40, 68–85 (2016). CrossRefPubMedGoogle Scholar

1. ↵

2. T. P. Weber,

3. N. I. Stilianakis

, Inactivation of influenza A viruses in the environment and modes of transmission: A critical review. J. Infect. 57, 361–373 (2008). CrossRefPubMedGoogle Scholar

1. ↵

2. N. van Doremalen et al.

, Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N. Engl. J. Med. 382, 1564–1567 (2020). CrossRefPubMedGoogle Scholar

1. ↵

2. A. W. H. Chin et al.

, Stability of SARS-CoV-2 in different environmental conditions. Lancet 1, E10 (2020). Google Scholar

1. ↵

2. K. A. Rychlik et al.

, In utero ultrafine particulate matter exposure causes offspring pulmonary immunosuppression. Proc. Natl. Acad. Sci. U.S.A. 116, 3443–3448 (2019). Abstract/FREE Full TextGoogle Scholar

1. ↵

2. G. Wu et al.

, Adverse organogenesis and predisposed long-term metabolic syndrome from prenatal exposure to fine particulate matter. Proc. Natl. Acad. Sci. U.S.A. 116, 11590–11595 (2019). Abstract/FREE Full TextGoogle Scholar

1. ↵

2. X. He et al.

, Temporal dynamics in viral shedding and transmissibility of COVID-19. Nat. Med. 26, 672–675 (2020). PubMedGoogle Scholar

1. ↵

2. D. Lewis

, Is the coronavirus airborne? Experts can’t agree. Nature 580, 175 (2020). Google Scholar

1. ↵

2. Y. Liu et al.

, Aerodynamic analysis of SARS-CoV-2 in two Wuhan hospitals. Nature, doi:10.1038/s41586-020-2271-3 (2020). CrossRefPubMedGoogle Scholar

1. ↵

2. L. Ferretti et al.

, Quantifying SARS-CoV-2 transmission suggests epidemic control with digital contact tracing. Science 368, eabb6936 (2020). Abstract/FREE Full TextGoogle Scholar

1. ↵

2. US Centers for Disease Control and Prevention

, Coronavirus Disease 2019 (COVID-19) - Social distancing, quarantine, and isolation. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/social-distancing.html. Accessed 9 May 2020. Google Scholar

1. ↵

2. L. Setti et al.

, SARS-Cov-2 RNA found on particulate matter of Bergamo in Northern Italy: First preliminary evidence. Environ. Res., doi:10.1016/j.envres.2020.109754 (2020).0013-9351 CrossRefGoogle Scholar

1. ↵

2. Z. An et al.

, Severe haze in northern China: A synergy of anthropogenic emissions and atmospheric processes. Proc. Natl. Acad. Sci. U.S.A. 116, 8657–8666 (2019). Abstract/FREE Full TextGoogle Scholar

1. ↵

2. L. A. Wallace,

3. S. J. Emmerich,

4. C. Howard-Reed

, Continuous measurements of air change rates in an occupied house for 1 year: The effect of temperature, wind, fans, and windows. J. Expo. Anal. Environ. Epidemiol. 12, 296–306 (2002). CrossRefPubMedGoogle Scholar

1. ↵

2. Q. Ye,

3. J. F. Fu,

4. J. H. Mao,

5. S. Q. Shang

, Haze is a risk factor contributing to the rapid spread of respiratory syncytial virus in children. Environ. Sci. Pollut. Res. Int. 23, 20178–20185 (2016). Google Scholar

1. ↵

2. Z. Gong et al.

, Probable aerosol transmission of severe fever with thrombocytopenia syndrome virus in southeastern China. Clin. Microbiol. Infect. 21, 1115–1120 (2015). Google Scholar

1. ↵

2. X. Wu et al

., Exposure to air pollution and COVID-19 mortality in the United States. https://projects.iq.harvard.edu/files/covid-pm/files/pm_and_covid_mortality.pdf. Accessed 9 May 2020. Google Scholar

1. ↵

2. S. Guo et al.

, Elucidating severe urban haze formation in China. Proc. Natl. Acad. Sci. U.S.A. 111, 17373–17378 (2014). Abstract/FREE Full TextGoogle Scholar

1. ↵

2. F. Zhang et al.

, An unexpected catalyst dominates formation and radiative forcing of regional haze. Proc. Natl. Acad. Sci. U.S.A. 117, 3960–3966 (2020). Abstract/FREE Full TextGoogle Scholar

1. ↵

2. J. Peng et al.

, Markedly enhanced absorption and direct radiative forcing of black carbon under polluted urban environments. Proc. Natl. Acad. Sci. U.S.A. 113, 4266–4271 (2016). Abstract/FREE Full TextGoogle Scholar

1. ↵

2. J. Howard et al.

, Face masks against COVID-19: An evidence review. https://doi.org/10.20944/preprints202004.0203.v2 (13 May 2020). Google Scholar