A more contagious coronavirus strain has been identified in 4 states and 33 countries. What we know.

A more contagious coronavirus variant first identified in the United Kingdom continues to crop up across the U.S. and around the globe, threatening to further strain overburdened health care systems just as vaccines are rolling out worldwide.

At least four U.S. states and 33 countries have identified the new variant, known as B.1.1.7. Several nations have also identified an additional variant, first identified in South Africa, that also appears to infect people more easily.

"Because the variants spread more rapidly, they could lead to more cases and put even more strain on our heavily burdened health care systems," said Dr. Henry Walke, incident manager for the Centers for Disease Control and Prevention's COVID-19 response.

"We need to be even more vigilant in our prevention measures to slow the spread of COVID-19."

Here's what we know about B.1.1.7.

How much more contagious is the new strain?

The strain first identified in the U.K. spreads more easily and quickly than other strains, according to the CDC. The strain was first spotted in September in southeastern England and accounted for a quarter of cases in London by November. By the week of Dec. 9, it was responsible for 60% of cases in the city.

What makes the new strain more contagious?

SARS-CoV-2, the virus that causes the disease COVID-19, acquires about one new mutation in its genome every two weeks, according to the CDC. The U.K. variant has several mutations that affect the "spike protein" on the virus surface that attaches to human cells.

"It’s able to bind to the receptors on cells better, and therefore is transmitted better," Dr. Anthony Fauci, the nation's leading infectious disease expert, said last week.

Is the new strain more lethal?

There is no evidence that B.1.1.7 causes more severe illness or increased risk of death, according to the CDC.

Is the vaccine effective for the new variant?

Researchers believe current COVID-19 vaccines will likely protect against B.1.1.7, but data is needed. The virus would "likely need to accumulate multiple mutations in the spike protein to evade immunity induced by vaccines or by natural infection," according to the CDC. ...

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