Coronavirus pandemic: WHO stumbles and some scientists see a pattern
At a press conference on Monday, a WHO official said that transmission of the coronavirus by people without symptoms is “very rare.” After the investigators’ concerted rejection, officials rejected the claim on Tuesday and said it was a “misunderstanding.”
But it is not the first time that the WHO assessment seems to be lagging behind scientific opinion.
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The agency delayed the endorsement of masks for the general public until Friday, alleging that there was very little evidence that they prevented transmission of the virus. Virtually all scientists and governments have been recommending masks for months.
The WHO has repeatedly said that tiny air droplets, or sprays, are not a significant factor in the spread of the pandemic, although a growing body of evidence suggests that they may be.
“The WHO has been out of step with most of the world on the issue of drops and sprays,” said Michael Osterholm, an infectious disease expert at the University of Minnesota.
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These scientific disagreements have broad political implications. Many countries, including the United States, adopted closure strategies because they recognized that isolating only people who were sick might not be enough to contain the epidemic.
If the virus is transmitted by small droplets in the air, people should continue to avoid congregating in poorly ventilated spaces, even if they practice rigorous hand hygiene.
The WHO has traditionally taken a cautious approach to evaluating scientific evidence. But the pace of research has changed: Scientists are now rushing to publish preliminary research, even before other experts can examine its results in depth.
The avalanche of findings can bring breakthroughs, like a vaccine, in record time. But the onslaught has also created confusion, including retractions from high-profile results.
“On the one hand, I want to reduce the WHO slack a bit, because it’s hard to do in an evolving pandemic,” said Dr. Ashish Jha, director of the Harvard Global Health Institute. “At the same time, we trust that WHO will provide us with the best data and scientific evidence.”
WHO’s thinking on asymptomatic transmission does not appear to have changed much since February, when the WHO Joint Mission to China reported that “the proportion of truly asymptomatic infections is unclear, but appears to be relatively rare and does not appear to be a factor important transmission. ”
Later, studies estimated that this number could reach 40%; The current best estimate from the Centers for Disease Control and Prevention is 35%. The research led many countries, including the United States, to endorse everyone’s use of masks.
But on Monday, Dr. Maria Van Kerkhove, WHO technical leader for the response to the coronavirus, said “it still seems rare for an asymptomatic person to be transmitted to a secondary individual.”
His statement elicited an immediate reaction from the scientists, who noted that study after study had shown transmission of the virus from people before they felt symptoms.
The reaction prompted WHO to clarify its position in a live session organized on Facebook and Twitter. Van Kerkhove said his comment was based on only two or three studies.
“I was answering a question; I was not establishing a WHO policy or anything like that,” he said. Van Kerkhove said his statement was also based on unpublished evidence that some countries have shared with the WHO.
But critics, including its own officials, said the organization should be transparent about its sources. “The first and main responsibility of WHO is to be the scientific leader,” said Lawrence Gostin, director of the WHO Collaborating Center on Global and National Health Law.
“And when they come up with things that the scientific establishment clearly contradicts without any justification or citing studies, it significantly reduces their credibility.”
A key point of confusion is the difference between people who are “pre-symptomatic” and will develop symptoms and those who are “asymptomatic” and never feel sick. Van Kerkhove suggested that his comments were about truly asymptomatic people.
A widely cited article published in April suggested that people are most infectious up to two days before the onset of symptoms, and estimated that 44% of new infections were the result of transmission from people who still had no symptoms.
The WHO refers to these people as pre-symptomatic. “Okay, technically okay,” said Jha. “But for all intents and purposes, they are asymptomatic, have no symptoms.”
Van Kerkhove said that by using the two terms, WHO officials are trying to be very clear about the group of people they refer to.
“Unfortunately, this is not how everyone uses it,” he said. “I had no intention of making things more complicated.”
The WHO continues to maintain that large respiratory drops expelled by sneezing or coughing are the main route of transmission and minimize the possible role of aerosols, smaller particles that can remain in the air.
But evidence is mounting that aerosols can be an important route.
“What they haven’t recognized is that activities like coughing and talking, even breathing in some cases, are also aerosol-producing procedures,” said Linsey Marr, who studies airborne virus transmission at Virginia Tech.
WHO officials said they knew that breathing and talking could lead to aerosols, but questioned its importance in spreading the virus.
“To date, transmission by this type of aerosol route has not been demonstrated,” said Dr. Benedetta Allegranzi, WHO technical leader on the coronavirus.
But the WHO defines airborne transmission in a very limited way, some scientists said. Airborne transmission also includes the possibility that the virus is in the air for shorter distances and is then inhaled.
“They have a very early view of the 20th century, very unsophisticated about what aerosols and airborne transmission are,” said Dr. Don Milton, an expert in public health aerobiology at the University of Maryland.
Until the 1950s, Milton said, tuberculosis was thought to be spread by prolonged close contact. “We now know that it is only transmitted by aerosols,” he said.
Some scientists suspect that the WHO position on masks and sprays may stem less from scientific research than from concerns about supplies of personal protective equipment for medical workers.
The organization currently recommends respirator masks that would block aerosols only for healthcare workers who perform medical procedures that produce aerosols.
Van Kerkhove said the WHO’s guidance was based only on science and not on any supply considerations. While EPP shortages are a problem, he said, “it doesn’t change what we recommend.”
All experts said it was not that the WHO was wrong on all counts, but that given the implications of their statements, they should be more cautious in concluding that transmission by air or by people without symptoms is not significant.
“We don’t know,” said Milton. “But they don’t know either.”
Some experts said that when the WHO uses the phrase “no evidence” to indicate uncertainty, it is in fact conveying certainty about the absence of a phenomenon.
Van Kerkhove admitted that point.
“That is a fair statement,” he said. “There is a lot of research that needs to be done to really understand this, and we are open to the fact that there is new research every day.”