At least 50% of COVID-19 infections come from people who do not show symptoms: study

A new study from the University of Chicago found that only 1 in 5 to 1 in 7 cases of the virus were symptomatic during the initial wave of the COVID-19 outbreak in New York. The research team found that asymptomatic cases contribute significantly to the transmission of the community, which accounts for at least 50% of the driving force behind SARS-CoV-2 infection. The results are on February 10 in the Proceedings of the National Academy of Sciences.

When the COVID-19 epidemic arrived in the US, investigators noted that it was very difficult to estimate what proportion of people infected with SARS-CoV-2 would develop symptoms, in part because of the initial challenges. with the test capability.

“Without testing the capacity data, it is very difficult to estimate the difference between cases that were not reported due to a lack of tests and cases that were actually asymptomatic,” said first author Rahul Subramanian, a Ph.D. . student in epidemiology at UChicago. “We wanted to disrupt the two things, and since New York City was one of the first cities to report the daily number of tests completed, we were able to use the numbers to estimate how many COVID-19 cases were symptomatic.”

Although there are a number of existing models that use epidemiological data to estimate unmarked case numbers and transmission rates, it is the first peer-reviewed model that contains data on daily testing ability and changes in testing rate over time to get a more accurate picture of which part of the SARS-CoV-2 infections are symptomatic in a large American city.

“The inclusion of this data in the model showed that the percentage of individuals symptomatic of COVID-19 is between 13% and 18%,” said senior author Mercedes Pascual, Ph.D., the Louis Block Professor of Ecology and Evolution by UChicago. “And regardless of uncertainty in all other parameters, we can see that more than 50% of the transmission in the community is of asymptomatic people – those who are asymptomatic and pre-symptomatic.”

Although this data analysis does not indicate how contagious asymptomatic individuals are, nor does it explain the new variants of the virus currently spreading in the US, the model provides additional support for the importance of following public health guidelines to address the transmission of the virus by the community to reduce individuals shows symptoms.

“Even if people without symptoms do not transmit the virus at high doses, it accounts for something like 80% of all infections,” says co-author Qixin He, now an assistant professor at Perdue University. “This relationship is quite surprising. It is crucial that everyone – including individuals who do not show symptoms – meet the guidelines for public health, such as wearing a mask and social distance, and that mass tests are made easily accessible to everyone.”

The investigators say these results also show that public health agencies need to make their test protocols and numbers publicly available to incorporate this data into existing transmission models.

“Making this information available is just as important as reporting the number of cases,” Pascual said. “Otherwise, we have a difference between the number and type of cases reported over time and the underlying transmission dynamics. These data are critical to epidemiological modeling.”