New versions of COVID-19 vaccines are now being tested in case they ever are needed to protect against mutated versions of the virus.

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The vaccines being rolled out across the U.S. offer strong protection, even against some of the variants becoming more common.

But viruses constantly evolve, and the world is in a race to vaccinate millions and tamp down the coronavirus before even more mutants emerge.

Researchers, hoping to stay ahead of these changes, are seeing whether tweaked versions of vaccines made by Moderna and Pfizer can protect against one worrisome type that emerged in South Africa.

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