Here’s what to know about the South African and U.K. virus variants.

In recent weeks, scientists have raised concerns about a coronavirus variant first detected in December in South Africa, noting that this version of the virus may spread more quickly than its cousins, and perhaps be harder to quash with current vaccines.

Their worries are compounded by skyrocketing Covid-19 cases in the United States and another highly infectious new variant that is driving a surge in Britain.

Scientists still have a lot to learn about these variants, but experts are concerned enough to warn people to be extra-vigilant in masking and social distancing. Here’s what you need to know:

The British variant has been found in about 50 countries, including the United States, where dozens of cases have been identified. The South African variant has spread to about 10 countries but has yet to be detected in the United States.

Both variants carry genetic changes in the virus’s spike protein — the molecule used to unlock and enter human cells — that could make it easier to establish an infection. Researchers estimate that the British variant is about 50 percent more transmissible than its predecessors. Julian Tang, a virologist at the University of Leicester, said that researchers didn’t yet have a good estimate for how much more contagious the South African variant is.

There is no evidence that any of the new variants are more deadly on their own, but an uptick in the spread of any virus creates ripple effects as more people become infected and ill. That can strain already overstretched health care systems and undoubtedly lead to more deaths.

It is unlikely that either variant will completely evade the protective effects of the new Covid vaccines. A recent study, not yet published in a scientific journal, found that the Pfizer-BioNTech vaccine is still effective against a virus carrying a mutation common to both new variants.

The South African variant does carry genetic changes that could make vaccines less effective: One mutation appears to make it harder for antibodies produced by the immune system to recognize the coronavirus, which means they may be less effective at stopping the variant. But it is “important to note that doesn’t mean vaccines won’t be functionally protective,” said Angela Rasmussen, a virologist affiliated with Georgetown University.

Vaccines use multifaceted immune responses, and while some antibodies may be confused by the variant, others probably won’t be. In addition, antibodies are only one sliver of the complex cavalry of immune cells and molecules that battle infectious invaders.

Also, if the virus accumulates more genetic changes, many of the authorized vaccines, including Pfizer’s and Moderna’s, can be adjusted fairly quickly.

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