Study: This is when you’re the most infectious with COVID-19

A recent study has put the spotlight on why it’s important to isolate immediately after you begin to have COVID-19 symptoms.

Researchers at the University of St. Andrews in the U.K. have confirmed that people infected with the disease caused by the coronavirus are most likely to be highly infectious within the first five days of symptoms developing.

The findings were published Thursday in The Lancet Microbe journal.

“This is the first systematic review and meta-analysis that has comprehensively examined and compared viral load and shedding for these three human coronaviruses. It provides a clear explanation for why SARS-CoV-2 spreads more efficiently than SARS-CoV and MERS-CoV and is so much more difficult to contain,” lead author Dr. Muge Cevik said in a statement.

Researchers primarily focused on people who were hospitalized and infected with the coronavirus, meaning the results only pertain to the isolation period and people confirmed to have COVID-19, according to a press release.

Key factors involved in understanding when patients are the most likely to be infectious are viral load, viral RNA shedding and isolation of the live virus.

Included in the analysis were 98 studies with at least five participants, randomized controlled trials and cohort studies. SARS-CoV-2 — the novel coronavirus — was the focus of 79 studies while 73 only focused on people who were hospitalized. Eight studies focused on SARS-CoV and MERS-CoV infection was the focus of 11 studies.

Scientists found that the SARS-CoV-2 viral load reaches its height at the beginning of the disease’s course, between the onset of symptoms and day five. On average, viral RNA shedding into the upper respiratory tract and lower respiratory tract lasted 17 and 14.6 days respectively. Viral RNA shedding is the length of time someone sheds genetic material.

Comparatively, the viral shedding for SARS-CoV and MERS-CoV peak at 10-14 days and 7-10 days after symptoms begin. This shows why the transmission of the viruses “can be effectively reduced by immediate identification, isolation and quarantine of people who show symptoms of the disease,” the press release said.

“Our findings are in line with contact tracing studies which suggest the majority of viral transmission events occur very early, and especially within the first 5 days after symptom onset, indicating the importance of self-isolation immediately after symptoms start,” Cevik said. “We also need to raise public awareness about the range of symptoms linked with the disease, including mild symptoms that may occur earlier on in the course of the infection than those that are more prominent like cough or fever.”