Most coronavirus cases are spread by people without symptoms, CDC now says

Most coronavirus infections are spread by people who have no symptoms, the US Centers for Disease Control and Prevention said in...

Posted: Nov 21, 2020 10:28 AM

Most coronavirus infections are spread by people who have no symptoms, the US Centers for Disease Control and Prevention said in newly updated guidance.

It's one of the main reasons mask use is so important, the CDC said.

"Most SARS-CoV-2 infections are spread by people without symptoms," the agency said in a section of its website devoted to explaining the science of how to use masks to control the spread of the virus.

"CDC and others estimate that more than 50% of all infections are transmitted from people who are not exhibiting symptoms," it added in the guidance posted Friday.

"This means at least half of new infections come from people likely unaware they are infectious to others."

According to the CDC, 24% of people who transmit the virus to others never develop symptoms and another 35% were pre-symptomatic. It also said 41% infected others while experiencing symptoms.

Peak infectiousness comes five days after infection, the agency said on the website. "With these assumptions, 59% of infections would be transmitted when no symptoms are present but could range (from) 51%-70% if the fraction of asymptomatic infections were 24%-30% and peak infectiousness ranged 4-6 days."

It cited a study published in July in the Proceedings of the National Academy of Sciences and as-yet unpublished CDC data. Previously, the health organization has not characterized what percentage of infections are spread by symptomless people.

"Infection is spread primarily through exposure to respiratory droplets exhaled by infected people when they breathe, talk, cough, sneeze, or sing," the agency added.

It also said people spew more droplets when they talk or sing louder or when they are exerting themselves more.

The CDC said studies have shown 40-45% of infected people never develop symptoms.

"Among people who do develop symptomatic illness, transmission risk peaks in the days just before symptom onset (presymptomatic infection) and for a few days thereafter."

"Accordingly, the number of infections transmitted peaks when virus levels peak," the agency noted.

So, people are spreading the virus when they have no idea they are infected.

Masks can prevent this spread.

Cloth masks can stop people from exhaling the little globs of mucus or saliva that carry the virus. Those particles can fly directly onto others, fall onto surfaces to be picked up, or linger in the air -- especially in closed rooms.

The CDC also now said masks can help prevent people from inhaling the droplets, large and small, that carry the virus.

New York Coronavirus Cases

County data is updated nightly.

Cases: 607001

Reported Deaths: 34362
CountyCasesDeaths
Queens866847343
Kings855617489
Bronx616175030
Nassau574892244
Suffolk573662036
Westchester476321502
New York429813222
Erie21873762
Richmond214321119
Rockland20824692
Orange16093517
Monroe13054313
Onondaga9470222
Dutchess6811185
Albany5233148
Broome4983135
Oneida4292146
Niagara3261103
Ulster310998
Chemung272432
Putnam252964
Schenectady218955
Sullivan210848
Saratoga200619
Steuben161087
Rensselaer155450
Chautauqua141416
Oswego13026
Ontario113537
Tioga105548
Wayne98312
Columbia97056
Tompkins9530
Cattaraugus91924
Cortland9131
Allegany86952
Madison83618
Genesee8198
Cayuga7627
St. Lawrence7059
Greene64618
Livingston6248
Herkimer60312
Chenango58310
Orleans58156
Otsego5528
Warren54735
Fulton46128
Jefferson4573
Washington43314
Clinton4305
Wyoming4305
Montgomery41312
Delaware3199
Lewis3159
Schuyler2743
Seneca2605
Essex25214
Franklin2436
Yates2427
Schoharie1762
Hamilton401
Out of NY0120
Unassigned017
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