Social Distancing, Masks Provide Significant Protection Against COVID-19

Investigators demonstrated that protection from COVID-19 transmission increases with physical distancing in an approximately linear proportion.

Using concepts of fluid dynamics and known factors in airborne transmission of coronavirus disease 2019 (COVID-19), investigators have confirmed that social distancing and mask-wearing measures provide significant protection.

In a study published in Physics of Fluids, investigators proposed the Contagion Airborne Transmission (CAT) inequality model designed to be accessible to the wider public, not just scientists and researchers. Although not all factors in airborne transmission are known, the model could be used to assess relative risks, since situational risk is proportional to exposure time.

The model is inspired by the Drake equation in astrobiology and develops a similar factorization based on the concept that airborne transmission occurs if a susceptible person inhales a viral dose exceeding the minimum infectious dose. Using this model, investigators demonstrated that protection from transmission increases with physical distancing in an approximately linear proportion.

“If you double your distance, you generally double your protection,” said author Rajat Mittal, PhD, in a press release. “This kind of scaling or rule can help inform policy.”

In addition to investigating whether distancing offers more protection, researchers also analyzed the protections offered by wearing masks. According to the press release, even simple cloth masks provide significant protection and could reduce the spread of COVID-19.

“We also show that any physical activity that increases the breathing rate and volume of people will increase the risk of transmission,” Mittal said. “These findings have important implications for the reopening of schools, gyms, or malls.”

The CAT model includes variables that can be added at each of the 3 stages of airborne transmission. They include the generation, expulsion, and aerosolization of the virus-containing droplets in an infected individual; the dispersion and transport via ambient air currents; and the inhalation of droplets or aerosols and the deposition of the virus in the respiratory mucosa of a susceptible person.

According to the press release, the investigators hope to continue analyzing face mask efficiency and the transmission details in high-density outdoor areas. The model based on CAT inequality could apply beyond COVID-19 as well, in the airborne transmission of other respiratory infections, such as the flu, tuberculosis, and measles.


Estimating risk of airborne COVID-19 with mask usage, social distancing [news release]. EurekAlert; October 26, 2020. Accessed October 28, 2020.

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