It spreads quickly
There’s still a lot we don’t know about Covid-19, but one thing is certain: It spreads like wildfire. The global tally now stands at more than 10.7 million infected, although the World Health Organization believes the true number is much higher, with one estimate stating 5 per cent to 8 per cent of the population has been infected.
One of the most important things to understand about the virus is how it spreads. Just like the flu, the new coronavirus can spread via sneezing and coughing. But some experts also worry that you can catch Covid-19 from someone talking, singing, shouting, or even just breathing heavily. “All the research is very, very new,” says Dr Teresa Murray Amato, an emergency medicine specialist. “We’re learning how to fly the plane while building it at the same time.”
Here’s what we know so far about how the virus itself flies—literally—between people and whether talking, especially loudly, to others, can really increase the risk of infection.
Covid-19 spreads from person to person
At the most basic level, experts believe that Covid-19 passes primarily between people who are in close contact with each other. As a respiratory virus, it lodges in the back of the throat and behind the nose then burrows into the bronchial tubes which lead to the lungs, explains Dr William Schaffner, an infectious disease specialist. A cough or sneeze from an infected person propels the virus, which hitches itself to respiratory droplets, into the air. Covid-19 is most easily transmitted when two people are within 1.8 metres of each other and inside, even if a person has no symptoms, a March 2020 study in Science China Life Sciences shows. Touching a contaminated surface then touching your eyes, nose or mouth can also spread the virus, though probably not as much. “To the best of our knowledge, these are the only two ways you can get infected with the virus,” says Dr Greg Poland, an expert with the Infectious Diseases Society of America (IDSA).
Respiratory droplets vs aerosol particles
Experts are now trying to figure out whether the virus spreads through respiratory droplets alone, or respiratory and aerosolized droplets. What’s the difference? Respiratory droplets are bigger and heavier than aerosolized particles so gravity pulls them earthward quickly, minimizing the time you could be exposed. Aerosolized particles, on the other hand, are smaller and lighter and float around for longer and travel farther, making them potentially infectious for longer, according to a March 2020 study in the New England Journal of Medicine (NEJM).
“Think of it as a sliding scale based on droplet size,” says Dr Poland, who is also a professor of medicine and infectious diseases at the Mayo Clinic, director of the Mayo Vaccine Research Group and editor-in-chief of the journal Vaccine. “The larger the droplet, like if I cough or sneeze, those generally fall out of the air in about 1.8 m to 3 m or less. Models show that aerosolized particles will spread in a cloud of about eight metres and linger in the air not for a minute or two but for 30 minutes or so.” An April 2020 NEJM study recorded that SARS-CoV-2 (the virus that causes Covid-19) aerosol bits stayed viable in the air for three hours, although its infectiousness did decrease.