“From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual,” Dr. Maria Van Kerkhove, head of the WHO’s emerging diseases and zoonosis unit, said at a news briefing (pdf).
“We have a number of reports from countries who are doing very detailed contact tracing,” she added. “They’re following asymptomatic cases. They’re following contacts. And they’re not finding secondary transmission onward. It’s very rare.”
She added that government responses should focus on people who have symptoms—including isolating them, and tracing down people who they may have come into contact with.
Undertaking this response can “drastically reduce” the reach of the CCP (Chinese Communist Party) virus, Van Kerkhove said.
The latest comments from the WHO suggests that asymptomatic spread is not the main way the CCP virus is being transmitted, and may in part assuage concerns that asymptomatic patients could be among the key drivers of the global spread of the virus.
It appears that Van Kerkhove was referring to asymptomatic cases only—where individuals never show symptoms—and not presymptomatic cases—where individuals don’t show symptoms at the time of being tested for the CCP virus, but develop symptoms later.
Van Kerkhove acknowledged that additional research is necessary to determine the prevalence of asymptomatic spread and how infectious asymptomatic patients are.
The latest report by the U.S. Centers for Disease Control and Prevention (CDC) on COVID-19 appears to suggest a stance that contradicts Van Kerkhove’s comment, saying that “a large number of persons with asymptomatic or mildly symptomatic infections were not detected by the health system and … these persons meaningfully contributed to ongoing community transmission.”
The U.S. Centers for Disease Control and Prevention (CDC) estimated in May that about 35 percent of COVID-19 cases are asymptomatic, and about 40 percent of transmissions happen before people show any symptoms.
Symptoms of COVID-19, the disease caused by the CCP virus, include fever, cough, shortness of breath or difficulty breathing, fatigue, muscle or body aches, headache, loss of taste or smell, a sore throat, congestion or runny nose, nausea or vomiting, and diarrhea, according to the CDC. It adds that patients may be infected and presymptomatic for two to 14 days after exposure to the virus.
The CDC notes that while anyone can experience mild to sever symptoms, those who are older and those with severe underlying medical conditions, such as heart or lung disease or diabetes, “seem to be at higher risk for developing more serious complications from COVID-19 illness.”
The majority of U.S. states had implemented lockdown and stay-at-home orders in March, largely to curb the spread of the CCP virus by mobile presymptomatic and asymptomatic COVID-19 patients, or those who remain in the community with mild symptoms.
The CDC in early April cited the “potential for presymptomatic transmission” as something that “underscores the importance of social distancing, including the avoidance of congregate settings” in reducing the spread of COVID-19.
“[T]o 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 said in its report at the time.
The CCP virus has spread to most countries around the world, claiming over 400,000 lives with over 7 million infections reported, according to government data collated by Johns Hopkins University.