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AT A TIME when many people have taken to washing hands and sanitising the objects they hold dear—frequently—a pesky question has loomed. How long does the SARS-CoV-2 virus stick around? A new paper in the New England Journal of Medicine, one of the first to examine the lifespan of the virus on common surfaces, offers some answers.

Like the common cold, covid-19 spreads through virus-laden droplets of moisture released when an infected person coughs, sneezes or merely exhales. A team of researchers, including scientists from America’s National Institute of Allergy and Infectious Diseases, simulated how an infected individual might spread the virus in the air and on plastic, cardboard, stainless steel and copper. They then measured how long the virus remained infectious in those environments.

They found that SARS-CoV-2 stays more stable on plastic and steel than on cardboard or copper. Traces of the virus were detected on plastic and steel up to three days after contamination. SARS-CoV-2 survived on cardboard for up to one day. On copper, the most hostile surface tested, it lasted just four hours (see chart). In the air, the team found that the virus can stick around for at least three hours. In the air, as elsewhere, the virus’s ability to infect people diminished sharply over time. In the air, for instance, its estimated median half-life—the time it takes for half of the virus particles to become inactive—was just over an hour. And the levels of the virus that do remain in the air are not high enough to pose a risk to most people who are not in the immediate vicinity of an infected person.

These findings are likely to assuage some fears. Homebound consumers worried about contagion from cardboard delivery boxes may have less to worry about the next time Amazon rings (unless they are used to same-day delivery). At the same time, the findings will amplify concerns about airborne transmission, which some experts had not considered possible. The research may change the way medical workers interact with infected patients, who with close contact may transmit the virus onto protective gear.

Why the virus can survive longer on some surfaces rather than others still remains something of a mystery. Maybe it has to do with the consistency of the object playing host to the virus. Cardboard, of course, is much more porous than steel, plastic or copper. But the authors noted that there was more variation in their experiment for cardboard than for other surfaces, and the results should be interpreted with caution. No doubt consumers are used to treating their surroundings that way by now.

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