Monday, June 8, 2020

UPDATE: WHO official says coronavirus carriers without symptoms rarely spread it to others; other experts say it's too early to say that; WHO now says scientists don't know actual rates of asymptomatic transmission

This article has been updated to reflect the World Health Organization's clarification that scientists have not yet determined how frequently people with asymptomatic cases of covid-19 pass it on to others. 

By Melissa Patrick
Kentucky Health News

Coronavirus patients without symptoms rarely spreads the virus to others, World Health Organization officials said at a news conference Monday (at about 31:35 on the YouTube video above).

"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, head of WHO's emerging diseases and zoonosis unit.

After strong pushback from public health experts, Van Kerkhove acknowledged at a WHO question and answer session Tuesday that scientists still don't know the actual rates of asymptomatic transmission, adding that when she said such spread is "very rare" she was referring to a very small subset of studies as well as data that has not been published, and stressed that her comments did not represent a new policy or direction.

"The majority of transmission that we know about is that people who have symptoms transmit the virus to other people through infectious droplets, "Van Kerkhove said. "But there are a subset of people who don't develop symptoms, and to truly understand how many people don't have symptoms, we don't actually have than answer yet."

The New York Times reports that a range of scientists said this assertion does not reflect current scientific research. “All of the best evidence suggests that people without symptoms can and do readily spread SARS-CoV-2, the virus that causes covid-19,” scientists at the Harvard Global Health Institute said in a statement on Tuesday.

They added, “Communicating preliminary data about key aspects of the coronavirus without much context can have tremendous negative impact on how the public and policymakers respond to the pandemic.” they said "a widely cited paper published in April suggested that people are most infectious about two days before the onset of symptoms, and estimated that 44 percent of new infections are a result of transmission from people who were not yet showing symptoms."

Current coronavirus policies are largely based on early evidence that indicated the virus could spread from asymptomatic carriers.

Guidance from the Centers for Disease Control and Prevention published April 1 cited "potential for presymptomatic transmission" as a reason for social distancing, including avoidance of congregate settings as a way to reduce the spread of the virus.

“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 study said.

But if asymptomatic transmission proves to not be an issue, this will have a huge impact on future policies, especially as Kentucky continues to re-open its economy and grapples with how to open its schools in the fall.

State Health Commissioner Steven Stack has said people in public should wear masks because one-fourth to one-half of people with the virus don't know they have it, and they can spread it even though they lack symptoms.

Stack didn't attend Gov. Andy Beshear's daily coronavirus briefing Monday. Beshear said he had not seen the report, and "That'll be something we have to look at and analyze." He said a cough from an asymptomatic person can spread the virus, and a mask can prevent that.

The governor said he would continue to wear a mask as long as he thinks it can protect someone else "whose body might not be able to handle this disease," not just from the science, but "in part based on faith, being my brother or sister's keeper, or faith that I know it can at least reduce it some."

Columbia University pediatrician and infectious-disease specialist Irwin Redlener told Brian Williams of MSNBC that the WHO should not have made a public statement on such a critcial issue until more research has been done.

Redlener said the statement failed to distinguish between people who are asymptomatic, who may never develop symptoms, and those who are pre-symptomatic, who develop symptoms later. Also, "People are not reliable reporters of whether they have symptoms," wrote Andy Slavitt, who headed the Centers for Medicare and Medicaid Services in the Obama administration. He said a research article in Nature "suggests people shed the virus most when people have the mildest of symptoms."

Van Kerkhove acknowledged that more research is needed to "truly answer this question" and some studies have indicated that the virus can spread via asymptomatic patients, but this is not the main way it is being transmitted.

“We have a number of reports from countries who are doing very detailed contact tracing,” Van Kerkhove said. “They’re following asymptomatic cases. They’re following contacts. And they’re not finding secondary transmission onward. It’s very rare.”

Van Kerkhove stressed the importance of contact tracing symptomatic patients as the best way to reduce the spread of the disease.

“What we really want to be focused on is following the symptomatic cases,” Van Kerkhove said. “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.

Meanwhile, Katherine Eban writes for Vanity Fair that negotiations have begun to reverse President Trump's withdrawal of the United States from the WHO. 

No comments:

Post a Comment