Pfizer announced Saturday that tweaking its COVID-19 vaccine to better target the omicron variant is safe and works — just days before regulators debate whether to offer Americans updated booster shots this fall.

The vaccines currently used in the U.S. still offer strong protection against severe COVID-19 disease and death — especially if people have gotten a booster dose. But those vaccines target the original coronavirus strain and their effectiveness against any infection dropped markedly when the super-contagious omicron mutant emerged.

Now with omicron’s even more transmissible relatives spreading widely, the Food and Drug Administration is considering ordering a recipe change for the vaccines made by both Pfizer and rival Moderna in hopes that modified boosters could better protect against another COVID-19 surge expected this fall and winter.

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