The WHO said asymptomatic transmission is 'very rare,' then said that was a 'misunderstanding.' Here's what you need to know.

• The WHO drew sharp criticism on Monday after saying that asymptomatic spread of the coronavirus is "very rare."
• In a follow up Q&A on Tuesday, the organization walked back the remarks, saying there was a "misunderstanding."
• It's still not clear how many truly asymptomatic patients (who never show signs of illness) might spread their disease to others.
• But a lot of people who are just coming down with the coronavirus are at their most infectious before they know they're sick, which is why the virus has spread so easily around the globe.

The World Health Organization is drawing confusion and outrage from many public health experts, after saying that asymptomatic spread of the novel coronavirus is "rare" during a regular press briefing on Monday.

"It still seems to be rare that an asymptomatic person actually transmits onward," epidemiologist Maria Van Kerkhove, WHO's technical lead for the coronavirus said. "We have a number of reports from countries who are doing very detailed contact tracing, they're following asymptomatic cases, they're following contacts, and they're not finding secondary transmission onward. It's very rare."

By Tuesday, the reactions from doctors, journalists, epidemiologists, and others on social media were so strong that the WHO sat down for a Q&A streamed live on Twitter, Facebook, and LinkedIn, to help clarify the remarks.

The WHO maintains that what was said was not in error, but perhaps the word asymptomatic was interpreted too broadly, to include people who may not yet be showing symptoms (pre-symptomatic), or people with very mild illnesses.

The agency also stressed that research on the coronavirus is rapidly evolving, and the comments were meant to speak only to a small number of studies and data sets, not the world's coronavirus patients at large, most of whom have not been studied at all.

"I used the phrase 'very rare,' and I think that that's a misunderstanding, to state that asymptomatic transmission globally is very rare," Van Kerkhove said on Tuesday. "What I was referring to was a subset of studies."

While the global public health organization maintained that they suspect, based on available evidence thus far, that the spread of coronavirus from people who never ever look and feel even a little bit sick appears to be rare, the experts acknowledged that some asymptomatic spreading does occur.

"That is occurring, I'm absolutely convinced that that is occurring," WHO's Executive Director of Health Emergencies Mike Ryan said Tuesday, during the Q&A. "The question is how much."

There are no clear answers yet as to how many truly asymptomatic people may go on to infect others, but some disease models suggest that as much as 40% of coronavirus transmission may be due to asymptomatic spreaders, the WHO said.

Asymptomatic transmission may be rare, but pre-symptomatic transmission is likely rampant

Adding another layer of confusion into the mix is the fact that many people are at their most infectious, and able to transmit their illnesses to others quite easily, right as they're learning they are sick. This so-called pre-symptomatic disease spreading is a major point of concern, because although patients do go on to develop clear symptoms of illness, they may not be feeling sick just yet, and thus are unknowingly out and about spreading their virus around to others.

One telling example: in May, officials in Seoul, South Korea traced as many as 40 coronavirus cases back to nightclubs after one man visited three of them, and later tested positive for COVID-19, the disease caused by the coronavirus.

"That means you could be in the restaurant, feeling perfectly well, and start to get a fever," Ryan said. "You didn't think you'd need to stay home, but that's the moment at which your viral load could be actually quite high ... It's because the disease can spread at that moment that the disease is so contagious. That's why it's spread around the world in such an uncontained way."

Van Kerkhove added that many coronavirus patients may not be fully asymptomatic, but might have very mild illnesses. Those individuals may have been classified as 'asymptomatic' in studies, but were not truly that, because they might have felt 'a little bit under the weather' and 'a little bit fatigued' but were not sick enough to know they had the virus for sure.

"When we say asymptomatic, we mean somebody that does not have symptoms, and does not go on to develop symptoms, truly no symptoms," she said.

The bottom line, the WHO stressed, is that social distancing, hand hygiene, avoiding touching your face, and contact tracing of symptomatic patients can go a long way to stop the spread of this virus, by catching a majority of illnesses and their viral shedding.

"There is enough stoppability in the virus," Ryan said. "It's not so transmissible that you cannot suppress."