The Number of COVID Patients Without Symptoms Is Growing, CDC Says
The number of people with coronavirus who don't have symptoms is more than the CDC initially believed.
For months people have wondered how common asymptomatic cases of the coronavirus are. Understanding the pervasiveness of people with COVID-19 who don't exhibit symptoms is essential to mitigating the spread since it's those people who are most likely to unknowingly infect others. The Centers for Disease Control and Prevention (CDC) has warned about asymptomatic spread even before they had a strong understanding of how much of an issue it was. But now, the CDC says that almost half of those infected with coronavirus are asymptomatic (40 percent, to be exact).
In May, the CDC created five "COVID-19 Pandemic Planning Scenarios" using data to estimate a range of possible trajectories for the coronavirus in the U.S. At that point, the CDC's "best estimate" was that 35 percent of cases were asymptomatic. Now, they've updated their predictions using new data through June 29. The CDC's "current best estimate" is that about 40 percent of people infected with the coronavirus show no symptoms of the disease, a notable 5 percent increase.
And that's not where the bad news ends. While in May, the CDC predicted that 40 percent of all coronavirus transmissions were coming from people without symptoms, they now say 50 percent of all cases stem from those who don't show any signs of the virus, either because they're asymptomatic or pre-symptomatic (meaning they eventually develop symptoms but don't have them at the time of transmission).
The question of asymptomatic spread has been a hot topic recently, ever since a World Health Organization (WHO) official claimed in June that it "seems to be rare that an asymptomatic person actually transmits onward to a secondary individual." However, WHO later walked back on that comment. "Whatever proportion of the disease is transmitting from asymptomatic individuals … is unknown," another official said the following day. But, he added, "that is occurring. I'm absolutely convinced that that is occurring."
There is also a bright spot in the CDC's updated assessments. The agency's current best estimate for the infectiousness of asymptomatic individuals—relative to symptomatic individuals—is now 75 percent, down from 100 percent in May.
While the CDC is using data to estimate these numbers, they emphasize that the true number of asymptomatic cases remains uncertain. "Asymptomatic cases are challenging to identify because individuals do not know they are infected unless they are tested, which is typically only done systematically as a part of a scientific study," says the CDC. And for more information on the spread of the coronavirus, check out This Is Who's Transmitting Over 50 Percent of COVID Cases, Study Finds.