NEW YORK (CBSNewYork)Mayor Bill de Blasio and health officials are urging people not to travel and celebrate Thanksgiving virtually as a way to beat back a possible second wave of COVID.

As CBS2’s Marcia Kramer reports, the key may be figuring out what’s causing an increase in infection, and it’s a key they just don’t have right now.

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“Probably around 50% we don’t have a way to check out the source of the infection and that’s a concern,” said Dr. Jay Varma, de Blasio’s senior advisor for public health.

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With the city’s COVID infection rates increasing, it was a stunning admission from Varma: While 10% of the city’s cases of COVID-19 can be traced to travel – down from 20% – 5% from small gatherings and 5% from congregate settings like nursing homes, health officials aren’t sure why more and more people are getting sick.

CORONAVIRUS PANDEMIC

Health Commissioner Dr. Dave Chokshi says it could “encountering someone who is infected but they don’t know it yet, meaning they are asymptomatic.”

The numbers, they say, are worrisome. Monday’s positivity rate was 2.88% and the seven day average 2.31%. That’s why they’re urging people to double up on precautions to prevent a second wave: Social distancing, wearing masks indoors, stay home – don’t travel for Thanksgiving.

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When Kramer asked Mayor de Blasio what would happen if we can’t beat back a second wave, he pointed to the seven day average of 2.31%.

“Obviously if that goes to 3%, schools would go all remote for a period of time,” he said. “I think there would be real concern about whether you can have businesses open on the same scale they are open now. You could see  restrictions in certain industries. You could see full scale closure. You could see a limit on hours. All these things are possible.”

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Because of the increasing infection rate, the city mounted a day of action on Staten Island and other parts of the city.

On a happier note, Mayor de Blasio said the Rockefeller Center Christmas tree will be lit as usual, and he’s working on a plan to allow people to see it safely.

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(© Copyright 2020 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)