4:13 PM, Feb 27, 2020


Ask Dr. Nandi: Could 50 percent of COVID-19 infections be spread by people who have no symptoms?

Posted at 10:48 PM, Jul 13, 2020

Could 50 percent of coronavirus infections be spread by people who have no symptoms? The answer is a yes, according to a published study by American and Canadian researchers.

Chief Health Editor Dr. Partha Nandi says the researchers looked at asymptomatic and presymptomatic transmission data. Remember asymptomatic means that you’re infected with the virus but that you have absolutely no symptoms and never feel sick. While presymptomatic refers to the time period when you’re infected but your symptoms haven’t yet started. Now, the research team entered this data into a mathematical model.

And they reproduced New York’s demography using 10,000 individuals. After simulating scenarios, their results showed that silent transmissions are responsible for more than half of COVID-19 outbreaks. And on top of that, they also pointed out that if you took all the people who had actually did have symptoms and isolated them, that silent transmission could still in fact cause and sustain outbreaks.

It is hypothetical and based on probabilities and approximations. But let’s take a look at another study that was published back in June. It focused on an Italian town where many of the residents were tested for the virus. And that study found that roughly 40% of people that tested positive did not have any symptoms.

The World Health Organization has previously said that asymptomatic transmission was likely “very rare.” But researchers pushed back, citing studies that have shown that this is in fact, possible. Now, the World Health Organization can lag behind because they tend to take a cautious approach. But, in their defense, scientific evidence is rapidly evolving because scientists around the world are racing to understand this virus. So in my opinion, here’s the key information you need to walk away with. When we’re all out and about whether working or running errands, you should assume that anyone around or near you could in fact be infected with the coronavirus but show no symptoms. So, I’m going to say this again - just like a broken record - please do your part to help slow transmission in our community. Stay 6 feet away from those who don’t live with you, wash your hands often, wear a mask, avoid crowded places, and any confined or enclosed spaces that have poor ventilation.

Additional Coronavirus information and resources:

Click here for a page with resources including a COVID-19 overview from the CDC, details on cases in Michigan, a timeline of Governor Gretchen Whitmer's orders since the outbreak, coronavirus' impact on Southeast Michigan, and links to more information from the Michigan Department of Health and Human Services, the CDC and the WHO.

View a global coronavirus tracker with data from Johns Hopkins University.

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See complete coverage on our Coronavirus Continuing Coverage page.