Viruses covered in “envelopes” have the most trouble surviving outside a living cell. On surfaces, the surrounding light, heat, and dryness break down the envelope, killing the virus. (Porous surfaces pull moisture away from viruses that land on them, accelerating the destruction of the envelope.) Most rhinoviruses have such envelopes; so do some influenza viruses. Norovirus doesn’t, enabling it to last longer in the environment.
Then there’s the new coronavirus. Its survival on surfaces is similar to that of the SARS virus, to which it’s related. On plastic, after eight hours only 10% of what researchers deposited was still there, according to a study published on Tuesday in the New England Journal of Medicine. But the virus didn’t become undetectable until after 72 hours. On stainless steel, the numbers began plummeting after just four hours, becoming undetectable by about 48 hours. On copper and cardboard, virus was undetectable by eight hours and 48 hours, respectively.
The fewer the virus particles on a surface, the lower the chances that someone touching it will become infected. But because the virus that causes COVID-19 is, like other microbes, so durable, throughly washing hands after touching surfaces that anyone else might have touched — or not touching them in the first place — is the first line of defense against infection.
This story was originally published by STAT, an online publication of Boston Globe Media that covers health, medicine, and scientific discovery.