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DENVER (NEXSTAR MEDIA WIRE/KDVR) – Studies of COVID-19 are in the early stages, and while many researchers say there are still unknowns, experts have learned a lot about the virus since March – now, researchers from the U.K. have released new data they say shows when people are most contagious after catching COVID-19.

The study, from researchers at the University of St. Andrews in Scotland, looks at viral load and viral shedding data – which help determine transmissibility – and found that those levels peak from around the time of the first symptoms to the fifth day after infection.

“When a person is infected with a virus, the virus multiplies in the body and can be released into the environment through sneezing, coughing or even speaking. This release is called “shedding” and viral shedding is how COVID-19 is spread from person to person,” writes the Mayo Clinic.

Since the outbreak began, it has remained unclear exactly how long infected individuals continue to shed the virus.

The St. Andrews team, led by Dr. Muge Cevik, looked at data from 98 studies on patients with three types of coronavirus – SARS-CoV-2, SARS-CoV and MERS-CoV. Seventy-nine of the studies were on patients with SARS-CoV-2, or COVID-19, but all had to have at least five participants, randomized controlled trials and cohort studies.

Viral shedding for the other two coronaviruses, known commonly as SARS and Middle East Respiratory Syndrome, doesn’t peak until a week or later after symptoms begin, allowing people to identify an infection and self-isolate before unknowingly passing it along. “This finding probably explains the efficient spread of SARS-CoV-2 compared with SARS-CoV and MERS-CoV,” the researchers stated.

With COVID-19, some patients never experience symptoms and others are already shedding the virus at a high rate just as symptoms start to arrive, the study says, making it easier to unknowingly pass the virus to someone else.

According to studies from the CDC, the coronavirus can continue to shed from a recovered person for up to 3 months after illness onset, but the new U.K. study determined that the live virus was found in patients for a much shorter time period.

“Our findings suggest that, although patients with SARS-CoV-2 infection might have prolonged RNA shedding of up to 83 days in upper respiratory tract infection, no live virus was isolated from culture beyond day 9 of symptoms despite persistently high viral RNA loads,” according to the paper.

The CDC has said that the available data from the studies indicates that someone with mild to moderate COVID-19 symptoms will no longer be infectious 10 days after the onset of symptoms.

A person with more severe to critical illness or a person severely immunocompromised will likely remain infectious no longer than 20 days after symptom onset, according to the CDC.

Once recovered, the CDC says a person can continue to shed detectable COVID-19 RNA in upper respiratory specimens for up to 3 months after the onset of the illness, even though the concentrations of COVID-19 are much lower than when the person is actually sick.

When it comes to someone who never develops symptoms, the CDC says isolation and other precautions can be discontinued 10 days after their first positive COVID-19 PCR test.

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