One unique characteristic of COVID-19 is that someone could be a carrier of the virus but not know it because they don’t show any symptoms. Those people are known as asymptomatic.
The Centers for Disease Control and Prevention define an asymptomatic case as an “individual infected with SARS-CoV-2 who does not exhibit symptoms during the course of infection,” but the CDC estimates that asymptomatic individuals are just as contagious as individuals who display symptoms. The center estimates that 35% of infections are asymptomatic.
Asymptomatic cases are different than—albeit similar to—when someone is presymptomatic, which the CDC defines as “an individual infected with SARS-CoV-2 who has not exhibited symptoms at the time of testing, but who later exhibits symptoms during the course of the infection.”
The CDC estimates that 40% of COVID-19 transmissions happen before people feel sick. For example, 46.5% of the 712 passengers and crew members on the Diamond Princess cruise ship who were infected with COVID-19 were asymptomatic at the time of testing, according to CNN.
CNN explains that asymptomatic people easily spread COVID-19 because the virus has a long incubation period. While the seasonal flu’s incubation period is one to four days, COVID-19’s is three to 14 days, with symptoms typically appearing “within four or five days after exposure,” according to Harvard Medical School.
“We know that a person with COVID-19 may be contagious 48-72 hours before starting to experience symptoms,” Harvard Health Publishing said. “Emerging research suggests that people may actually be most likely to spread the virus to others during the 48 hours before they start to experience symptoms.”
On June 8, the World Health Organization threw experts into confusion when officials from the organization said that “coronavirus patients without symptoms aren’t driving the spread of the virus,” according to CNBC News. They also said it is “rare that an asymptomatic person actually transmits onward to a secondary individual.”
But the WHO walked back that statement the next day and said there had been a “misunderstanding,” according to the Washington Post.
“I wasn’t stating a policy of WHO or anything like that,” Maria Van Kerkhove, head of the WHO’s emerging disease and zoonosis unit, said. “We do know that some people who are asymptomatic, or some people who do not have symptoms, can transmit the virus on.”
Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, told ABC’s Good Morning America that the WHO’s original statement was incorrect.
“We know from epidemiological studies they can transmit to someone who is uninfected even when they’re without symptoms,” Fauci said. “So to make a statement to say that’s a rare event was not correct.”
Because research still shows that anyone can contract the virus and then spread it unknowingly, anyone going out in public should wear a mask and practice social distancing.