New study: 59% of COVID cases stem from asymptomatic spread

A new study by the Journal of the American Medical Association (JAMA) found that 59% of COVID cases stemmed from asymptomatic spread. This includes 35% from people who infect others before they show symptoms and 24% from people who never develop any symptoms. The key findings were a part of an ongoing study to determine what percentage of the current pandemic were made more complicated due to individuals showing no COVID symptoms spreading the virus to others.

“The bottom line is controlling the COVID-19 pandemic really is going to require controlling the silent pandemic of transmission from persons without symptoms,” Jay Butler, one of the study authors and the CDC (Centers for Disease Control and Prevention) deputy director for infectious diseases, told The Washington Post.

“Those findings are now in bold, italics and underlined,” he said. “We’ve gone from 11-point font to 16-point font.”

In every scenario tested, the model consistently found more than half of all transmissions were caused via symptomatic individuals.

“In addition to identification and isolation of persons with symptomatic COVID-19, effective control of spread will require reducing the risk of transmission from people with infection who do not have symptoms,” the study stated. “These findings suggest that measures such as wearing masks, hand hygiene, social distancing, and strategic testing of people who are not ill will be foundational to slowing the spread of COVID-19 until safe and effective vaccines are available and widely used.”

Sources: JAMA, CDC and the Washington Post