■ Tweaked COVID-19 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.

What’s happening

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 toward an alternative if the virus eventually outsmarts today’s shots.

“We need to be ahead of the virus,” said Dr. Nadine Rouphael of Emory University, who is helping to lead a study of Moderna’s tweaked candidate. “We know what it’s like when we’re behind.

“It’s not clear if or when protection would wane enough to require an update but, “realistically we want to turn COVID into a sniffle,” she added.

About the variants

Viruses constantly evolve, and the world is in a race to vaccinate millions and tamp down the coronavirus before even more mutants emerge. More than 119 million Americans have had at least one vaccine dose, and 22% of the population is fully vaccinated, according to the Centers for Disease Control and Prevention. Much of the rest of the world is far behind.

Already an easier-to-spread version found in Britain just months ago has become the most common variant now circulating in the United States, one that’s fortunately vaccine-preventable.

But globally, there’s concern that first-generation vaccines may offer less protection against a different variant that first emerged in South Africa. All the major vaccine makers are tweaking their recipes in case an update against that so-called B.1.351 virus is needed. Now experimental doses from Moderna and Pfizer are being put to the test.

How they’re doing it

In suburban Atlanta, Emory asked people who received Moderna’s original vaccine a year ago in a first-stage study to also help test the updated shot. Volunteer Cole Smith said returning wasn’t a tough decision.

“The earlier one, it was a great success and, you know, millions of people are getting vaccinated now,” Smith said. “If we’re helpingpeople with the old one, why not volunteer and help people with the new one?”

The study, funded by the National Institutes of Health, isn’t just testing Moderna’s experimental variant vaccine as a third-shot immune booster. Researchers at Emory and three other medical centers also areenrolling volunteers who haven’t yet received any kind of COVID-19 vaccination.