June 8 (UPI) -- Editor's note: On Tuesday, the World Health Organization's Maria Van Kerkhove clarified her remarks, calling the depiction of asymptomatic spread of COVID-19 as "rare" a "misunderstanding." Read the updated story here.
The spread of COVID-19 from people who have no symptoms appears to be "very rare," the World Health Organization said Monday.
Research shows that many patients, particularly young and otherwise healthy people, may carry the virus but have no symptoms or very mild symptoms, said Maria Van Kerkhove, head of WHO's emerging diseases and zoonosis unit, at a news briefing from Geneva, Switzerland.
"From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual," Van Kerkhove said. "A number of countries are not finding secondary transmission. It's very rare."
Patients who carry the virus but have no symptoms, or very mild symptoms, have been identified through contact tracing, Van Kerkhove said.
She acknowledged that a study of cases in Singapore showed that outbreaks appeared to spread from asymptomatic patients in clusters found in long-term facilities and in family units.
"We're trying to get more information from countries to answer this question," she said.
"What we really want to be focused on is following the symptomatic cases," Van Kerkhove added. "If we actually followed all of the symptomatic cases, isolated those cases, followed the contacts and quarantined those contacts, we would drastically reduce the outbreak."
COVID-19 is transmitted from person-to-person through vapor droplets from sneezing or coughing, the U.S. Centers for Disease Control and Prevention has said. Studies of clusters in nursing homes in King County, Wash., and elsewhere seemed to show that people without symptoms, or who would later develop symptoms, should be quarantined if they have been exposed.
"The potential for presymptomatic transmission underscores the importance of social distancing, including the avoidance of congregate settings, to reduce COVID-19 spread," the CDC said in April.
In countries like New Zealand, where the government said COVID-19 has been eliminated, health officials aggressively identified people with symptoms of the disease and isolated them.
After a 75-day lockdown, New Zealand has gone 17 days without detecting a new case within its borders and 12 days without a patient in hospital sickened, Prime Minister Jacinda Ardern announced Sunday.
Worldwide, the number of reported infections passed 7 million, Sunday, with more than 400,000 deaths.
The number of active cases in the United States reached 1.95 million Monday, with more than 110,000 deaths, according to the Johns Hopkins University online COVID-19 tracker.