The concern that SARS-CoV-2 could be spread by people without symptoms originally came from a single case report. It was alleged that an asymptomatic woman from China had spread the virus to 16 other contacts in Germany. Later reports showed that, at the time of contact, this woman was taking medication for flu-like symptoms, invalidating the evidence provided for the theory of asymptomatic transmission. As with other common respiratory viruses, SARS-CoV-2 spreads by being exhaled, coughed or sneezed into the air. The largest droplets fall quickly and settle on the ground whilst the most lightweight particles, known as aerosols, may remain suspended in the air for days. Once the virus is present in the environment, it spreads by finding its way into the respiratory tract of new hosts in a large enough quantity (known as the ‘viral load’ or ‘infectious dose’) to infect them. The theory of fomite transmission (touching contaminated surfaces and then touching the face) is not supported by scientific evidence.
…In asymptomatic individuals, the viral load is typically very low and the infectious period is also short in duration. They may still exhale virus particles, which another person may encounter. However, the overall likelihood of transmitting the disease to others is negligible. Thus asymptomatic cases are not the major drivers of epidemics. As Dr Anthony Fauci of the US National Institute of Allergy and Infectious Diseases stated in March 2020: ‘In all the history of respiratory-borne viruses of any type, asymptomatic transmission has never been the driver of outbreaks. The driver of outbreaks is always a symptomatic person.’