Tweaked COVID vaccines in testing aim to fend off variants

Dozens of Americans are rolling up their sleeves for a third dose of COVID-19 vaccine—this time, shots tweaked to guard against a worrisome mutated version of the virus. Make no mistake: The vaccines currently being rolled out across the U.S. offer strong protection. But new studies of experimental updates to the Moderna and Pfizer vaccines mark a critical first step […]
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