Covid-19’s duration varies widely depending on severity, but now we know the rough range

In the early weeks of the Covid-19 crisis, little was known about the wide range of possible symptoms and the typical progression of the disease. Now, more than three months into the coronavirus outbreaks, doctors and researchers are finally getting a handle on the typical duration of the illness and how it plays out.

It all starts when a person is infected by SARS-CoV-2. The virus, entering most often through the mouth, nose, or eyes, gets into the respiratory system and incubates before announcing itself through symptoms. This incubation is a bit like a chicken egg developing before it hatches.

Covid-19 is known to take anywhere from two to 14 days before it triggers symptoms, with a median of four to five days, according to the U.S. Centers for Disease Control and Prevention. There are known exceptions, up to 19 days. During incubation, a person can be infectious. It’s not yet known how early the period of infectiousness starts, but this period of “viral shedding” is thought to typically begin two to three days before symptoms start, and reach a maximum around day five for mild cases and around day 10 for severe cases, according to one small study on early data, published in the journal Nature.

When the virus does take hold, the onset of symptoms is typically gradual, so a person may not realize they have Covid-19 for up to three weeks after they’ve contracted it.

A person might start out with mild or moderate symptoms. “Then on days 5 to 9 it can really explode in those people who are destined to develop severe disease.”

“For those three weeks, that individual can spread the virus, because they may not be sick, or they may not feel too sick,” says Mark Cameron, PhD, an immunologist and medical researcher in the School of Medicine at Case Western Reserve University in Ohio. “So you’ve got a perfect storm scenario for the spread of this virus.”

While there is no typical case, there are a range of scenarios, illustrated in the graphic below.

• At its most brief, the virus might incubate for just two days, and a person might have a mild case of Covid-19 lasting just two weeks, for a total duration of 14 days from infection.
• In more severe cases, a person might suffer anywhere from three weeks (light orange in the graphic) to six weeks.
• Among those who die, the final outcome can come as quickly as two weeks after symptoms start, or up to eight weeks later. Add a possible 14-day incubation period, and the longest likely scenario, then, is 10 total weeks from the time of infection to a person’s death.

How symptoms progress

For Covid-19 patients who have symptoms, the effects can vary widely. The most common symptom among those who have been diagnosed is fever, followed by cough, then fatigue, and in more severe cases, shortness of breath and other symptoms. But some people never experience more than mild cold- or flu-like symptoms. Some people lose their sense of smell with Covid-19 while experiencing no other symptoms, doctors are reporting. Some 80% of diagnosed cases involve only mild to moderate symptoms.

The progression can come in phases. A person might start out with mild or moderate symptoms, explains Robert Salata, MD, a professor of medicine in epidemiology and international health at Ohio’s Case Western Reserve University. “Then on days five to nine it can really explode in those people who are destined to develop severe disease.”

Negative tests are no guarantee the effects of the illness are over, either.

“For severe cases, and cases that end up in the hospital, we’re seeing quite a significant time lag between symptoms first arriving and the patient weakening and requiring hospital care,” says Caroline Buckee, associate professor of epidemiology at Harvard T.H. Chan School of Public Health.

Scientists don’t know all factors involved in severe cases, but they do know that underlying health conditions, including heart disease, diabetes, and respiratory issues, raise the risk of a severe case.

It’s also possible that the “viral dose” matters in determining whether a case becomes severe or not. That means someone who is exposed to a lot of the virus for an extended period of time, such as a health care worker, is at greater risk than someone inhaling a small amount.

How do we know when someone is virus-free?

Much remains to be studied about when symptoms are gone and a person “feels better” versus when they are no longer infectious, especially among people who have mild or no symptoms.

In most diagnosed cases, a swab test looking for the virus performed seven days after the onset of symptoms will be positive, Salata says. A test 10 days after symptom onset will typically come back negative, suggesting the person is virus-free. But there have been outlier cases of people testing positive up to 37 days after symptom onset, he says.

Half of people treated for mild Covid-19 infections harbored the coronavirus up to eight days after symptoms disappeared, according to a March 27 study in the American Journal of Respiratory and Critical Care Medicine.

Negative tests are no guarantee the effects of the illness are over, either.

“We have seen individuals with some lingering respiratory symptoms, including cough, even though they tested negative,” Salata says. The presumption when these conflicting signs appear is that the person is symptomatic but no longer infectious, he says, but that’s not known for certain.

A vaccine for Covid-19 is thought to be many months away. Meantime, a ray of hope: Multiple clinical trials underway now, at Case Western and several other institutions, should soon reveal treatments that can decrease the severity of Covid-19 symptoms in some people and, importantly, shorten the duration of both symptoms and infectiousness.

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