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A top World Health Organization official clarified on Tuesday that scientists have not determined yet how frequently people with asymptomatic cases of Covid-19 pass the disease on to others, a day after suggesting that such spread is “very rare.” The clarification comes after the WHO’s original comments incited strong pushback from outside public health experts, who suggested the agency had erred, or at least miscommunicated, when it said people who didn’t show symptoms were unlikely to spread the virus. (Joseph, 6/9)

A comment by a WHO official on Monday — calling such asymptomatic transmissions “very rare” — touched off a furious scientific debate over the unresolved question and attracted widespread criticism of the organization. Less than 24 hours later, the WHO convened a special news conference to walk back its comments, stressing that much remains unknown. But the comment from Monday had already spread widely and been seized upon by conservatives and others to bolster arguments that people do not need to wear masks or maintain social distancing precautions. (Wan and Berger, 6/9)

Another distinction Van Kerkhove made in clarifying Tuesday is that she was referring to truly asymptomatic people, and not people who are presymptomatic, meaning they do not have symptoms at the moment but will later. Presymptomatic people and those with mild illness that someone might not even notice can transmit the virus, meaning that someone should not assume the absence of symptoms means they are not infectious. "People who are not showing symptoms can still spread the disease; it's just that they're likely pre-symptomatic rather than truly asymptomatic," tweeted Jeremy Konyndyk, senior policy fellow at the Center for Global Development. "Keep wearing those masks. Keep distancing." (Sullivan, 6/9)

But the ripple effects of her initial comments already had public health specialists perplexed. For months, scientists have said that even people without obvious symptoms can transmit the virus, and that these asymptomatic people carrying the disease are potentially part of the global pandemic. (Johnson, 6/10)

Some public health experts noted Kerkhove’s failure to support her claim with published studies, while others rushed to her defense. “It makes sense,” Dr. Faheem Younus, chief of infectious diseases at the University of Maryland Upper Chesapeake Health, said on Twitter. “Each cough may emit ~3000 and sneeze ~40,000 droplets from a symptomatic patient. The risk is much less with asymptomatic.” (Rodriguez, 6/9)

The controversy comes at a tumultuous time for the WHO. President Donald Trump said last month blasted the agency's coronavirus response and said the U.S. would withdraw its support. A Trump administration official confirmed U.S. funding to the WHO has been suspended. Several prominent Republicans jumped on Van Kerkhove’s initial statements as evidence the United States could safely, and completely, reopen. “Good News! People who catch coronovirus but have no symptoms rarely spread the disease. Translation: sending kids back to school does not require millions of test kits,” Sen. Rand Paul (R-Ky.) tweeted on Monday. His tweet has been shared more than 11,000 times and liked at least 25,000 times as of Tuesday afternoon. (Ehley, 6/9)

Another big question is what proportion of people are truly asymptomatic and never progress to having any symptoms and what proportion reported as asymptomatic actually have mild disease. "We're 6 months into a pandemic, there's a huge amount of research that's being done, but we don't have that full picture yet," Van Kerkhove said. (Schnirring, 6/9)

Studies show people with the coronavirus are most infectious just at the point when they first begin to feel unwell, World Health Organization (WHO) experts said on Tuesday. This feature has made it so hard to control spread of the virus that causes COVID-19 disease, but it can be done through rigorous testing and social distancing, they said. “It appears from very limited information we have right now that people have more virus in their body at or around the time that they develop symptoms, so very early on,” Maria van Kerkhove, a WHO epidemiologist and technical lead on the pandemic, told a live session on social media. (Nebehay, 6/9)

Even as the World Health Organization leads the worldwide response to the coronavirus pandemic, the agency is failing to take stock of rapidly evolving research findings and to communicate clearly about them, several scientists warned on Tuesday. In a news briefing on Monday, a W.H.O. official asserted that transmission of the coronavirus by people without symptoms is “very rare.” Following concerted pushback from researchers, officials on Tuesday walked back the claim, saying it was a “misunderstanding.” (Mandavilli, 6/9)