Rattankun Thongbun/iStockBy EMILY SHAPIRO and AARON KATERSKY, ABC News

(NEW YORK) -- In New York City, which was the U.S. epicenter of the COVID-19 pandemic last spring, the mayor is asking residents to wear two masks until at least June.

"Through June, keep doing exactly what you are doing," Mayor Bill de Blasio said Tuesday. "Not just wear a mask, wear two. Social distancing, get tested monthly. If you do have a case in your home, have the person safely separate."

The Centers for Disease Control and Prevention said earlier this month that layering a well-fitting cloth mask over a surgical mask is likely beneficial. Research suggested that when a person "double masks" -- wearing a polypropylene surgical mask with a cloth mask on top -- and the people around them did the same, the risk of transmitting the virus falls more than 95%. The benefit fell to 80% if only one person wore the double mask.

De Blasio said, "June is when we want to hit 5 million New Yorkers fully vaccinated and June is the earliest we would even consider changing guidance around masks. It may be that we continue that guidance for quite a while depending on what is going on. We are very concerned about the variants -- that's a big X factor."

New York City reported 3,254 new cases on Tuesday and 233 new hospitalizations. The city's positivity rate stands at 7.32%.

"We cannot take our foot off the gas right now," New York City Health Commissioner Dr. Dave Chokshi said.

"We now have the valuable new weapon in our arsenal, the vaccine, but we have to think about it as something that is an additional layer of protection -- and that includes mask wearing," Chokshi said.

"Two masks and higher grade masks should become more common among New Yorkers," he said, adding that vaccinated New Yorkers should still wear masks, too.

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