A model developed by CDC researchers estimates that 59% of coronavirus cases in the United States are spread by asymptomatic carriers. Transmissions from individuals who have not yet begun to exhibit signs of infection account for 35% of that total, while transmissions from people who never develop symptoms make up the other 24%.

A model developed by CDC researchers estimates that 59% of coronavirus cases in the United States are spread by asymptomatic carriers. Transmissions from individuals who have not yet begun to exhibit signs of infection account for 35% of that total, while transmissions from people who never develop symptoms make up the other 24%. “The bottom line is controlling the COVID-19 pandemic really is going to require controlling the silent pandemic of transmission from persons without symptoms,” said Jay C. Butler, CDC’s deputy director for infectious diseases. He emphasized the continued importance of existing “community mitigation tools” such as hand hygiene, mask wearing, social distancing, and coronavirus testing—even for people who do not feel sick. The model, which assumed that asymptomatic carriers were 75% as contagious as people with obvious signs of infection, is published in JAMA Network Open.