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Moderna COVID-19 vaccine

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The Moderna COVID-19 vaccine received an emergency use authorization from the FDA in December 2020, but the biotech company has continued to develop the shot — and it expects the next version to produce fewer side effects.

The challenge: The Moderna COVID-19 vaccine is a marvel of modern medicine — the result of decades of research and development on mRNA vaccines. Just six weeks after the novel coronavirus's genome was first sequenced, Moderna was able to have a vaccine candidate ready for testing, and after proving incredibly effective in trials, it was authorized for use less than a year later.

That efficacy has held up in the real world, too — the shot has helped slash case numbers in places where it's been widely deployed — but there's still room for improvement.

The Moderna COVID-19 vaccine is the same type of shot as Pfizer's authorized vaccine, but people who receive it report more side effects. The reason for that is pretty straightforward: each Moderna dose contains more than three times the amount of vaccine.

Going with a high dose out the gate was a way for Moderna to improve its chances of the vaccine meeting efficacy targets during the first round of trials. But thanks to Pfizer's shot and Moderna's own trials, the company now knows that it can achieve the same results with less vaccine.

Smaller vaccine dose: Moderna is currently trialing versions of its vaccine that have been tweaked to protect against specific variants of the coronavirus, administering them as both stand-alone vaccines and boosters for people who received the company's initial shot.

These trials include doses half as large as the one currently authorized in the U.S., and Moderna is already making deals with manufacturers to produce doses of that size.

"We're assuming that as of 2022, we are going to have a mix of dose levels on the market," a Moderna spokesperson told Reuters.

It's not unheard of to have different doses of a vaccine. The flu shot has a high-dose formulation, with four times the regular dose, which is available to older people whose immune systems don't respond as strongly to the standard flu shot.

"There's a long history of second-gen vaccines being multiply improved over first-gen vaccines."

Scot Roberts

Why it matters: Smaller doses of the Moderna COVID-19 vaccine should mean fewer side effects, which could help decrease vaccine hesitancy, at least in the U.S., where side effects are a primary reason people give for passing on the shot.

The switch would also mean doubling the number available doses, since the same amount of vaccine could be used for twice as many shots.

The bottom line: The currently authorized vaccines have already proven to be game-changers in the battle against COVID-19, but expect Moderna and other developers to continue to improve upon their initial creations.

"There's a long history within vaccinology of second-generation vaccines being multiply improved over first-generation vaccines," Scot Roberts, CSO of biotech company Altimmune, told USA Today. "That's just the way things go."

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