You Can Catch COVID From Someone This Many Days After Their Symptoms Begin

New research from the CDC shows how long cases are infectious.

The coronavirus spreads easily from person-to-person, and experts are still trying to fully grasp all there is to know about transmission. One of the biggest points of discussion is exactly when an infected person can spread COVID-19 to other people. Not only can an ill person infect someone else, but studies have also found that people can spread the virus before they are symptomatic and even if they never experience any symptoms at all. And now, new research from the Centers for Disease Control and Prevention (CDC) reveals that you can catch COVID from someone up to 20 days after their symptoms begin.

The CDC released their report on the infectious time period of COVID-19 on July 22. One of the studies the CDC used to determine this timeframe—which was pre-released on June 9 and has not yet been peer-reviewed—observed 129 hospitalized COVID-19 patients and found that the range of days for viral shedding in these patients was anywhere from zero to 20 days after symptoms first appeared. However, the probability of someone spreading the virus 15 days after symptom onset dropped below five percent.

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People can start being infectious before they develop symptoms, but once they do, the CDC says that the infectious period of the virus starts to decline. And typically, patients with mild or moderate COVID-19 cases don't remain infectious after 10 days following symptom onset. So who can spread the coronavirus for up to 20 days? Those with a severe COVID-19 case, according to the CDC.

"A limited number of persons with severe illness may produce replication-competent virus beyond 10 days that may warrant extending duration of isolation and precautions for up to 20 days after symptom onset," the CDC report states. "Recovery of replication-competent virus between 10 and 20 days after symptom onset has been documented in some persons with severe COVID-19 that, in some cases, was complicated by immunocompromised state."

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However, this is not the first time the CDC suggested that immunocompromised people may be able to spread COVID-19 longer than others. In a report from May 14, the organization stated that immunocompromised people "may remain infectious for a longer period of time than others with COVID-19" but emphasized that they could not confirm that until more research was conducted. And it ended up being backed up by the June 9 study, of which 30 out of the 129 patients were immunocompromised.

"Infection prevention and control guidelines should take into account that patients with severe or critical COVID-19 may shed infectious virus for longer periods of time compared to what has been reported for in patients with mild COVID-19," the study states. The CDC has recently updated its quarantining guidelines to say that infected people can leave self-isolation 10 days after first discovering symptoms. However, these finds suggest that those with more serious symptoms should consider staying in quarantine for a full 20. And for more on transmission, check out If You're This Age, You're Most Likely to Infect Loved Ones With COVID.

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