Experts from the Bruno Kessler Foundation in Trento, Italy, in collaboration with colleagues affiliated to the ATS Lombardy COVID-19 Task Force and various research institutions, conducted a study assessing what percentage of people who have contracted SARS-CoV-2 are likely to experience any symptoms. This preliminary study does not yet appear in a peer-reviewed journal, but its authors have made their findings available online, on the preprint platform arXiv.
The rate of likely asymptomatic carriers of the coronavirus could have important implications for viral transmission, the study authors point out. “This work allows us to clearly show the difficulties in identifying infections with surveillance since the majority of these are not associated with respiratory symptoms or fever,” says study co-author Stefano Merler, who specializes in mathematical modeling of infectious disease transmission.
The researchers analyzed data on 5,484 individuals from the Lombardy region of Italy who had been in contact with people with a new coronavirus infection. Of these, 2,824 individuals had laboratory-confirmed SARS-CoV-2 infections. Looking at the data, the investigators found that, of the 2,824 individuals with known coronavirus infections, only 876 (31%) had presented any symptoms. Looking at data on age, the researchers calculated that, among people aged 20 years and under, a probable 81.9% would present no symptoms following infection with the coronavirus.