March 23, 2020: News reports of a recent study on the new coronavirus, published last week in the New England Journal of Medicine, have prompted several questions from members of the MIT community. If COVID-19, can live for up to three days on some surfaces and may remain suspended in the air for as long as a half hour, how safe are home-delivered groceries? Mail? Take-out food?
How about fresh air? “Should I stop walking outdoors, even if I take precautions to be 6 feet away from a passerby?” one person asked us.
When it comes to surfaces, researchers found that the virus lives longest on plastic and steel, up to 72 hours. It lasted only four hours on copper but up to 24 hours on cardboard. But as horrifying as that might sound, it’s important to remember that not all the virus deposited on a given surface remains viable for the same length of time. Even on stainless steel and plastic, the half-life of the virus — the length of time it takes for half the microbes in a given sample to die — was 5.6 and 6.8 hours respectively. On cardboard it was less than four hours.
“While grocery bags, mail, and packages could, theoretically, have small amounts of infectious viral particles on them, the risk is relatively low,” says Medical Director Cecilia Stuopis. “If you’re worried, wash your hands after opening packages or mail. Likewise, any small risk from take-out containers can be mitigated by transferring the food to your own dishes, disposing of the packaging in which it was delivered, and washing your hands before eating.”
The risk from potentially aerosolized virus is also thought to be low. While the research showed the virus remaining airborne longer than originally thought, it also showed that it disperses quickly, meaning that unless you are physically close to an infected person who is coughing or sneezing, you are unlikely to be at risk from viral aerosols.
So, by all means, go for that walk! Exercise and fresh air is important for both physical and mental health, especially at a time when most of us are hunkering down in our homes for so many hours every day. Your risk of becoming infected by a stray bit of airborne virus while out on a walk and maintaining a safe distance from others is minimal.