Viral load and contact heterogeneity predict SARS-CoV-2 transmission and super-spreading events

SARS-CoV-2 is difficult to contain because many transmissions occur during pre-symptomatic infection. Unlike influenza, most SARS-CoV-2-infected people do not transmit while a small percentage infect large numbers of people. We designed mathematical models which link observed viral loads with epidemiologic features of each virus, including distribution of transmissions attributed to each infected person and duration between symptom onset in the transmitter and secondarily infected person. We identify that people infected with SARS-CoV-2 or influenza can be highly contagious for less than 1 day, congruent with peak viral load. SARS-CoV-2 super-spreader events occur when an infected person is shedding at a very high viral load and has a high number of exposed contacts. The higher predisposition of SARS-CoV-2 toward super-spreading events cannot be attributed to additional weeks of shedding relative to influenza. Rather, a person infected with SARS-CoV-2 exposes more people within equivalent physical contact networks, likely due to aerosolization.

Automated summary

SARS-CoV-2 is difficult to contain due to pre-symptomatic transmissions, with a small percentage of infected individuals causing large outbreaks. Infected individuals with SARS-CoV-2 or influenza may be highly contagious for less than a day, typically corresponding to peak viral load. Super-spreader events of SARS-CoV-2 occur when infected individuals shed virus at a very high load and have numerous contacts, potentially due to aerosol transmission.