May 11: MIT Medical answers your COVID-19 questions. Got a question about COVID-19? Send it to us at CovidQ@mit.edu, and we’ll do our best to provide an answer.
Can we get the virus by handling our deliveries, which are usually packed in bags or boxes upon their arrival? We are aware that the virus lives for many hours and/or days on different surfaces but we also know that experts say that the virus is generally spread from person to person. Can you clarify?
It’s theoretically possible to pick up the virus from a surface, but you’re right that it is usually spread from one person to another. Here’s why:
Since COVID-19 is caused by a respiratory virus carried in respiratory droplets, transmitting the virus directly from one person to another is a simple, one-step process: An infected individual expels viral-laden respiratory droplets while another, nearby individual breathes them in. To try to prevent this type of transmission, we wear face coverings and try to maintain at least a six-foot distance between others and ourselves.
In contrast, becoming infected from a contaminated surface, like a recently delivered bag of groceries, requires the successful completion of a complex, multi-step process: An area of the bag becomes contaminated with a sufficiently infectious amount of virus; you come in direct contact with that contaminated area; you transfer a sufficient number of viral particles to your hands; and, finally, you use your hands to transfer that virus directly to your mucus membranes.
Let’s look at this process in a little more detail. First, to contain a sufficiently infectious number of viral particles, the bag would have to have been contaminated relatively recently. Although studies have found detectable levels of the virus remaining on surfaces for a significant amount of time, a “detectable” amount is not necessarily the same as an infectious amount. We don’t know how many viral particles are required to transmit an infection, but we do know that this virus degrades rapidly outside the body. Regardless of surface type, the half-life of the virus — the time required for half of the viral particles to die — is measured in a matter of hours, not days.
And even if your grocery bag has an infectious amount of virus on it, those particles would likely be concentrated in only one or two small areas. So, the next step requires some precision. You would need to come into direct contact with the contaminated spot, or spots, on the bag, and you would also need to pick up a sufficiently infectious amount of virus when you do.
But you can’t get sick just from getting viral particles on your hands. To contract the virus, you would then need to transfer those viral particles — again, in sufficient number — to your mucus membranes, either by touching your mouth or your nose (or maybe your eyes) with your contaminated hands.
So, yes, it may be possible to get sick this way, but it’s clear why this is not the primary way the virus is spread. And this mode of transmission is completely preventable: Just wash your hands immediately after touching any surface that has any possibility of being contaminated. Remember, you can’t get the virus just by touching it. You also have to get it from your hands to your respiratory system, and that connection is readily broken with soap and water.