Covid-19 Patients Are ‘Highly Infectious’ Within Five Days Of Showing Symptoms, Study Shows, Explaining Pandemic’s Rapid Spread


Covid-19 is a “short-lived” infection that lasts for only nine days after patients begin to show symptoms, according to a new study that shows patients to be “highly infectious” very early on in the illness, peaking within five days of showing symptoms—a time period so short that researchers believe it can explain why the pandemic has been so hard to contain and how it has managed spread so quickly. 

Key Facts

The research, published in Lancet Microbe, indicates that patients have high levels of “live” virus — which is capable of replicating and potentially infecting others — within the first five days of showing symptoms, with none detected after nine days.

These high levels of live virus suggest Covid-19 patients are “highly infectious” early on, highlighting the need for rapid contact tracing and isolation.

Though no live virus was detected after nine days, fragments of viral genetic material could, in some cases, be detected for weeks afterwards, leaving some tests used to determine infectiousness inaccurate.   

Dr. Muge Cevik, the study’s lead author, said that the findings suggest repeat PCR testing — the accurate laboratory test used to detect viral genetic material — may not be appropriate to determine whether someone is no longer infectious and able to stop self-isolating, as results “could remain positive for much longer and [do] not necessarily indicate they could pass on the virus to others.”

Crucial Quote

Cevik said: “The findings are in line with contact tracing studies which suggest the majority of viral transmission events occur very early, and especially within the first five days after symptom onset, indicating the importance of self-isolation immediately after symptoms start.” He urged the need to raise awareness about Covid-19 symptoms, which include loss of smell and taste, a high temperature and a new, continuous cough, so that individuals can be aware and self-isolate.

Surprising Fact

The “short-lived” infectiousness of Covid-19 offers an explanation as to why it has been so hard to contain when compared to other coronaviruses like MERS or SARS, researchers say. The viral load of Covid-19, i.e. how much live virus there is, peaks much earlier than these other coronaviruses, typically within the first five days. For MERS this is 7-10 and SARS 10-14 days after symptoms begin, giving public health officials much more time to track and isolate potential contacts. 

Further Reading

SARS-CoV-2, SARS-CoV, and MERS-CoV viral load dynamics, duration of viral shedding, and infectiousness: a systematic review and meta-analysis (Lancet Microbe)

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