Is COVID-19 Transmitted by Respiratory Droplets or Aerosolized Droplets?

SPRINGFIELD — There is a new international debate surrounding COVID-19 and the spread of the infection.

The Centers for Disease Control and Prevention (CDC) and other health organizations have long thought that the novel coronavirus is spread mainly from person to person between people who are in close contact within one another (about six feet). This spread is through respiratory droplets produced when an infected person coughs, sneezes, or talks. These droplets can land in the mouths, noses or eyes of people who are nearby or be inhaled into the lungs. Some recent studies have suggested that COVID-19 may be spread by people who are not showing symptoms.

Now, in a letter sent to the World Health Organization (WHO) signed by more than 200 scientists, they claim that aerosolized droplets floating in the air can cause infection. They urged WHO to react to what they claim is “mounting evidence.”

“They are raising the specter that COVID-19 could theoretically be transmitted by the airborne route,” said Dr. Sarah Haessler, lead epidemiologist and infectious-disease specialist for Baystate Health.

Aerosols are small particles that can remain suspended in air for longer periods of time than most respiratory secretions and are small and light enough to sometimes travel longer distances. Certain viruses, such as smallpox and measles, and bacteria, such as the agent that causes tuberculosis, are expelled as aerosols and can therefore be transmitted by the airborne route.

Most respiratory viruses are transmitted by the droplet route, which means they are expelled as larger particles that are heavier and fall to the ground in a span of three to six feet from an infected person. This is where the social-distancing recommendation of six feet derives, Haessler noted. For these agents, a facemask is appropriate protection (along with eye coverings, gloves, gowns, etc., especially for healthcare workers).

“In the hospital, we use a special type of respirator mask called N95, which is required for protection when treating patients whose viruses can become aerosolized,” she explained.

According to Haessler, the letter to WHO mainly represents the opinion of laboratory scientists and researchers, many of whom are from particle science and other engineering-type disciplines and basic — but, importantly, not clinical — science positions.

“While it may be accurate that, under certain laboratory conditions, the COVID-19 virus can form aerosols, there is scant data to present to suggest that this infection is generally transmitted that way,” she said. “In fact, the preponderance of actual clinical and epidemiologic information — including data from our own experiences at Baystate over the past four months of the pandemic — strongly suggest that this virus is primarily transmitted by respiratory droplets.”

Haessler has reassurance for the public who may have read about the debate and the letter sent to WHO, and who are worried about their protection from the virus.

“Universal masking, hand hygiene, and social distancing are still the main ways to prevent the spread of COVID-19, since clinical data strongly suggests the virus is mainly transmitted through respiratory droplets, as we have known since the early beginnings of the novel coronavirus data,” she said. “To further stop the virus and protect yourselves and others, remember to wear a mask when around others, keep a safe distance from others, cover your coughs and sneezes, and wash your hands often.”