The Science Behind A 14-Day Quarantine After Possible COVID-19 Exposure
To stop the spread of the coronavirus, health officials have a favorite refrain: After being in a city or region where there have been a lot of COVID-19 cases, spend 14 days in quarantine even if you feel perfectly fine — don’t leave your house. Coming from New York? 14-day quarantine. Arriving in Hawaii? 14-day quarantine. Been in Italy or China or Iran recently? 14-day quarantine.
“That’s a long-standing public health practice, and it’s called ‘traveler’s quarantine,’ ” explains Lindsay Wiley, a professor at American University’s Washington College of Law. “Fourteen days is not a made-up number here — it’s based on what we know so far about COVID-19, and it’s possible that over time we’ll see that number change as we learn more [about the virus].”
The 14-day rule is widespread because public health agencies around the world work together on these guidelines. In the U.S., the Centers for Disease Control and Prevention sets the quarantine period, and its counterpart organizations do so abroad, all in concert with the World Health Organization.
If you’re one of the many people who are being asked to quarantine for a fortnight, you might be asking: Why 14 days, exactly?
The answer has to do with how viruses invade cells and replicate.
Once a virus infects someone — a host — it takes some time for the virus to make enough copies of itself that the host begins to shed the virus, through coughs or sneezes, for instance. (That’s the way the host helps the virus spread to other people — who are then new hosts.) This is the virus’ incubation period. For us hosts, it’s generally the time between when we’re first infected and when we start shedding the virus, which may be a little before we start experiencing symptoms.
“The incubation period varies from virus to virus and sometimes from host to host,” says Rachel Graham, a virologist at the University of North Carolina’s Gillings School of Global Public Health.
For the virus that causes COVID-19 — its official name is SARS-CoV-2 — researchers have found that the typical incubation period is about five days. About 97% of the people who get infected and develop symptoms will do so within 11 to 12 days, and about 99% will within 14 days.