4 Out of 5 People With COVID-19 Will Develop Symptoms: Study

TUESDAY, Sept. 22, 2020 (HealthDay News) -- Folks shrugging off the risk of COVID-19 because they don't think the virus will do them much harm might want to think again.

As many as four out of five people infected with the new coronavirus likely will suffer some symptoms of COVID-19, a new analysis shows.

Only about 20% of infected people remain symptom-free while they carry the new coronavirus, according to a review of 79 COVID-19 studies. These studies involved just over 6,600 people, of whom 1,287 remained asymptomatic.

These results support the moves that have been taken to impede the spread of SARS-CoV-2, said Dr. Len Horovitz, a pulmonary specialist with Lenox Hill Hospital in New York City.

"Masks, social distancing, hand-washing and avoiding crowds -- we know these are the four things that really will mitigate the spread," Horovitz said.

The new figure of around 20% is at the low end of previous estimates of asymptomatic COVID-19 cases, said Dr. Susan Kline, a professor of infectious diseases with the University of Minnesota in Minneapolis.

"I thought it was somewhere between about 15% and 50%," Kline said. "I think this is a nice paper because it has pulled in a lot of different articles and then they show how all their estimates vary and they point out some of the differences in the way the studies were set up."

However, Kline sees the glass as half-empty rather than half-full.

"I would say 20% is still a fairly large number," Kline said. "I don't think it really changes our guidance that everyone should wear a mask, which was primarily to prevent those with asymptomatic infection from spreading it to others, especially in public places."

But Horovitz and other experts said the jury's still out on how many COVID-19 patients truly remain asymptomatic throughout their infection.

Horovitz noted that these studies were conducted between March and June, when widespread testing for COVID-19 in the United States remained largely unavailable.

"When you talk about asymptomatic patients you really have to talk about the number of tests that have been taken, because if you're under-testing people, you're not going to uncover the asymptomatic people," Horovitz said.

But after more widespread testing over a greater period of time in the United States, Horovitz believes that "the asymptomatic rate seems to be more like 40% than 20%."

It's also possible some people aren't asking for the test because their symptoms resemble a less worrisome condition, said Dr. Amesh Adalja, a senior scholar with the Johns Hopkins Center for Health Security in Baltimore.

"Many people who think they are asymptomatic are misattributing mild symptoms to something other than COVID," Adalja said. "Nevertheless, the new study doesn't change public health guidance but underscores the need to more fully understand the factors that are involved in whether symptoms develop."

The true answer of how many people don't suffer symptoms when they have COVID-19 will be answered when widespread testing is available in the United States and around the world, Horovitz said.

The new review was published online Sept. 22 in the journal PLOS Medicine.

More information

The U.S. Centers for Disease Control and Prevention has more about COVID-19.