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WHO clarifies comments on asymptomatic spread of coronavirus: 'There's much unknown'

The World Health Organization tried on Tuesday to clear up confusing comments about how often people can spread the coronavirus when they do not have symptom...

Posted: Jun 9, 2020 5:06 PM

The World Health Organization tried on Tuesday to clear up confusing comments about how often people can spread the coronavirus when they do not have symptoms.

The organization held a live Q&A on its social media pages to address questions about comments made by a WHO official that suggested asymptomatic people only rarely spread Covid-19.

The comments appeared to directly contradict guidance from public health organizations, including the US Centers for Disease Control and Prevention, which have said about a third of coronavirus infections may be asymptomatic. The CDC also estimates that 40% of coronavirus transmission is occurring before people feel sick, meaning they are presymptomatic.

But it may boil down to how one defines "asymptomatic."

'There are so many unknowns'

Maria Van Kerkhove, WHO's technical lead for coronavirus response and head of its emerging diseases and zoonoses unit, said during a media briefing in Geneva on Monday that "it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual."

But then on Tuesday, during the live Q&A, she clarified "this is a major unknown."

"The majority of transmission that we know about is that people who have symptoms transmit the virus to other people through infectious droplets -- 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 that answered yet," Van Kerkhove said.

"We do know that some people who are asymptomatic, or some people who don't have symptoms, can transmit the virus on," she said. "So what we need to better understand is how many of the people in the population don't have symptoms and separately how many of those individuals go on to transmit to others."

On Monday, Van Kerkhove had said that what appear to be asymptomatic cases of Covid-19 often turn out to be cases of mild disease.

"When we actually go back and we say how many of them were truly asymptomatic, we find out that many have really mild disease," Van Kerkhove said on Monday.

"They're not quote-unquote Covid symptoms -- meaning they may not have developed fever yet, they may not have had a significant cough, or they may not have shortness of breath -- but some may have mild disease," Van Kerkhove said. "Having said that, we do know that there can be people who are truly asymptomatic."

Van Kerkhove added that she was referring to reports from WHO member states when she made her comments on Monday.

"What I was referring to yesterday in the press conference were very few studies -- some two or three studies that had been published that actually try to follow asymptomatic cases, so people who are infected, over time, and then look at all of their contacts and see how many additional people were infected," Van Kerkhove said.

"And that's a very small subset of studies. So I was responding to a question at the press conference. I wasn't stating a policy of WHO or anything like that," she said. "Because this is a major unknown, because there are so many unknowns around this, some modeling groups have tried to estimate what is the proportion of asymptomatic people that may transmit."

How the virus spreads

Dr. Mike Ryan, executive director of the WHO Health Emergencies Program, also said during the live Q&A that there is still much to learn about the possible asymptomatic spread of the coronavirus.

"Whatever proportion of disease is transmitting from asymptomatic individuals, as Maria said, that is unknown," Ryan said.

"I'm absolutely convinced that that is occurring. The question is how much," he said. "There's much to be answered on this. There's much that is unknown."

'Trying to slice the salami very fine'

Whether someone is presymptomatic or or simply experiencing very mild symptoms is not of importance to the person on the receiving end of the transmission, said Dr. William Schaffner, a Vanderbilt University professor and longtime adviser to the CDC.

"I thought they were getting very prissy and trying to slice the salami very fine," Schaffner said about WHO's comments on Monday on asymptomatic spread.

"You can be vertical and feel 100% or virtually 100% and going about your daily business and unaware that you're infected and perfectly capable transmitting the virus," Schaffner said. "How do we inhibit transmission of the virus by these people who are doing their full range of normal activities? The answer is social distancing and wearing masks and good hand hygiene and stay away from crowds. That's the formula."

Liam Smeeth, professor of clinical epidemiology at the London School of Hygiene and Tropical Medicine, said that he was "quite surprised" by Van Kerkhove's original comments.

"It goes against my impressions from the science so far that suggest asymptomatic (people who never get symptoms) and pre-symptomatic people are an important source of infection to others," Smeeth said In a written statement distributed by the UK-based Science Media Centre on Tuesday.

"This is the main basis for steps such as self-isolation and lockdown -- steps we know, from yesterday's two Nature papers have massively reduced the numbers of people infected and have prevented millions of deaths globally," he said. He was referring to research that estimates shutdown measures through early April prevented more than 500 million coronavirus infections across six countries.

"There remains scientific uncertainty, but asymptomatic infection could be around 30% to 50% of cases," Smeeth said. "The best scientific studies to date suggest that up to half of cases became infected from asymptomatic or pre-symptomatic people."

Mississippi Coronavirus Cases

Data is updated nightly.

Cases: 248189

Reported Deaths: 5411
CountyCasesDeaths
DeSoto16841171
Hinds15890312
Harrison13037191
Rankin10439205
Jackson10128177
Lee8721135
Madison8071160
Jones6166108
Forrest5870117
Lauderdale5724177
Lowndes5238109
Lafayette486192
Lamar475363
Washington4734122
Bolivar3941106
Oktibbeha388179
Panola360475
Pontotoc358752
Monroe3487103
Warren337895
Union337457
Marshall336065
Neshoba3325150
Pearl River319492
Leflore2980104
Lincoln293385
Sunflower277569
Tate266659
Alcorn260651
Itawamba258858
Pike258176
Hancock253557
Prentiss242450
Scott241043
Yazoo237754
Copiah237449
Tippah236246
Simpson232367
Leake227864
Coahoma223154
Grenada215770
Covington208871
Marion206171
Adams201666
Winston198061
George197438
Wayne196130
Attala191658
Newton186542
Chickasaw181243
Tishomingo179659
Holmes167867
Jasper165134
Clay156732
Stone140218
Tallahatchie138234
Clarke136460
Calhoun133321
Smith118823
Yalobusha113834
Walthall111136
Noxubee109622
Greene108929
Montgomery108134
Carroll103721
Lawrence101217
Perry99131
Amite96425
Webster90624
Claiborne85125
Tunica84521
Jefferson Davis83825
Humphreys81524
Benton80323
Kemper75720
Quitman6758
Franklin65315
Choctaw59613
Wilkinson58125
Jefferson53019
Sharkey42417
Issaquena1586
Unassigned00

Alabama Coronavirus Cases

Cases: 417528

Reported Deaths: 6030
CountyCasesDeaths
Jefferson61313888
Mobile29768542
Madison26637185
Tuscaloosa20580268
Montgomery18696304
Shelby18310113
Baldwin16002179
Lee12261101
Morgan12093112
Etowah11604157
Calhoun10982200
Marshall10108107
Houston8474129
Cullman7960104
Limestone790174
Elmore7723101
DeKalb764697
St. Clair7460120
Lauderdale745183
Talladega6102108
Walker5852174
Jackson574441
Blount526483
Colbert525670
Autauga510355
Coffee434256
Dale391081
Franklin363445
Chilton333565
Covington326167
Russell323810
Escambia312442
Dallas300296
Clarke278233
Chambers277869
Tallapoosa2599107
Pike245829
Marion240549
Lawrence240447
Winston223835
Bibb213047
Geneva197431
Marengo197329
Pickens195231
Hale173742
Barbour171236
Butler167958
Fayette166026
Cherokee159630
Henry151119
Monroe144417
Randolph138535
Washington136526
Clay125246
Crenshaw118044
Lamar116619
Cleburne116023
Macon113335
Lowndes108735
Wilcox101221
Bullock98128
Perry95419
Conecuh92920
Sumter88726
Greene75323
Coosa60414
Choctaw51224
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