Spread of the coronavirus by asymptomatic patients is “very rare,” the World Health Organization said Monday, calling into question research that suggested asymptomatic cases could be spreading the disease on a large scale.
“From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual,” said Dr. Maria Van Kerkhove, who leads the WHO’s diseases and zoonosis unit, during a press briefing in Geneva, where WHO is headquartered.
“We have a number of reports from countries who are doing very detailed contact tracing,” Van Kerkhove continued. “They’re following asymptomatic cases. They’re following contacts. And they’re not finding secondary transmission onward. It’s very rare.”
Van Kerkhove said that while additional research and data is necessary to determine how much the coronavirus can spread through people with no symptoms, governments should focus on those who are experiencing symptoms, making sure they isolate and tracing their contacts with other people.
“If we actually followed all of the symptomatic cases, isolated those cases, followed the contacts and quarantined those contacts, we would drastically reduce” the scope of the pandemic, Van Kerkhove remarked.
An April 1 Centers for Disease Control and Prevention suggested that asymptomatic patients could be a hidden factor causing the spread of pathogen causing the respiratory illness in others.
“These findings also suggest that to control the pandemic, it might not be enough for only persons with symptoms to limit their contact with others because persons without symptoms might transmit infection,” the CDC report said.
In May, the CDC estimated that around a third of coronavirus cases are asymptomatic and as much as 40 percent of coronavirus person-to-person transmissions occur before individuals experience any symptoms.
The WHO said its initial assumption was that asymptomatic individuals are equally contagious as those with symptoms.
In March, the majority of U.S. states issued lockdown and stay at home orders, shutting down large swaths of the economy largely to prevent asymptomatic people as well as those with mild coronavirus symptoms from unknowingly spreading the virus.