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Coronavirus Variants: What We Know So Far

New strains are more contagious, but there’s no evidence of more severe COVID-19 illness

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En español | Public health officials have identified two strains of the coronavirus that are more contagious, worrying experts who say they could lead to a surge in COVID-19 cases just as vaccinations are getting underway. 

The first strain, known as B.1.1.7., was discovered in the United Kingdom but is now circulating in more than 30 countries, including the United States. 

The other variant was discovered in South Africa and is mostly circulating in Africa. 

Experts say early data indicate the current COVID-19 vaccines are likely to be effective against both variants.

There is no evidence that the new strains cause more severe illness or increased risk of death, the Centers for Disease Control and Prevention (CDC) said. 


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“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 Henry Walke, M.D., incident manager for the CDC’s COVID-19 response team.

How did these new COVID-19 strains develop?

Because viruses multiply rapidly, new mutations are always occurring, said William Schaffner, M.D., an infectious diseases specialist at Vanderbilt University Medical Center in Nashville, and medical director of the National Foundation for Infectious Diseases (NFID). 

Most of these tiny genetic changes have no effect on the behavior of the virus. 

The new variants discovered in the U.K. and South Africa stood out because they spread more easily, Schaffner said, so they can rapidly replace other versions of the virus and become dominant. 

Are the new strains more dangerous?

Neither of the new strains has been shown to cause more severe illness or a greater risk of death. 

Because they’re more contagious, however, they may be able to infect more people more quickly, potentially increasing overall hospitalization and death rates.


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Scientists estimate the U.K. variant is 40 to 70 percent more transmissible than the traditional COVID-19 virus. Its spread has led to a rapid spike in cases in England; figures released on Jan. 5 showed that 1 in 50 people there have recently been infected with the virus.

Will the COVID-19 vaccine work against the new strains?

Based on what they know now, experts expect the current COVID-19 vaccines to work.

“Early data indicate the vaccines will protect against both variants of the virus,” Schaffner said.

Scientists are continuing to test vaccine effectiveness against both strains; if necessary, vaccines can be modified quickly to better match any variants.

What precautions should you take? 

The guidance about how to protect yourself from COVID-19 hasn’t changed: Wear a mask, wash your hands, practice social distancing, avoid crowds and stay home if you can.

“These two strains reinforce the importance of all of the standard interventions we’ve been talking about, because they work,” Schaffner said. “And when it comes your turn to get the vaccine, by all means get the vaccine.”

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