A COVID vaccine grown in plants measures up

A vaccine from a Canadian biotech firm Medicago has been found to be effective at preventing moderate to severe disease. It could soon become the first plant-based vaccine authorized for human use.

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A Canadian biotech firm is reporting positive results from a large study of its COVID-19 vaccine. If approved by regulators, it will be the first human vaccine made in plants. NPR's Joe Palca has more.

JOE PALCA, BYLINE: The trick with vaccines is to show the immune system something that looks like a virus but isn't. The Canadian firm Medicago does that by growing something called virus-like particles. They look like the COVID virus, but they can't actually infect you. And by grow, I mean grow. Medicago makes its vaccine in a plant related to tobacco. And the vaccine seems to be working.

BRIAN WARD: We think it's a good vaccine. Even if I weren't working for them, (laughter) I would think it was a good vaccine.

PALCA: Brian Ward is the medical officer for Medicago. He says they now have initial results from a study of some 24,000 volunteers. Half got the vaccine, half a placebo.

WARD: We had about 74%-78% efficacy to prevent moderate and severe disease.

PALCA: The vaccine did slightly worse, closer to 70% efficacy, if you look at preventing any COVID disease. But Ward says there's something important to keep in mind - the Medicago vaccine was designed to cope with the original strain of the virus.

WARD: All of the cases in our study were caused by these new variants.

PALCA: Most of the cases were from the delta or gamma variants. Omicron hadn't yet appeared on the scene when the study was conducted. Ward says other vaccines have also had lower efficacy in combating the variants. He also says the side effects from the Medicago vaccine were similar.

WARD: Pretty much everybody gets a sore arm.

PALCA: Ward says the sore arm is probably due to something called an adjuvant that's added to the vaccine to rev up the immune response. One thing they saw very little of was the fever that sometimes accompanies other COVID-19 vaccine shots. Medicago plans to ask Canadian regulators for authorization to distribute its vaccine. In the meantime, Ward says, they're getting supplies of the vaccine ready.

WARD: We have commercial lots being filled into vials as we speak.

PALCA: But manufacturing capacity is an issue. Right now, the plants making the virus-like particles are grown in North Carolina. Ward says he's confident that they'll be able to supply the 76 million doses they've already promised to the Canadian government, and he says they're building a new facility with much greater capacity.

WARD: And if we're still stuck with a COVID problem by late 2023, then our major global facility will come online in Quebec City.

PALCA: Unfortunately, the world may indeed still be stuck with COVID then.

Joe Palca, NPR News.

(SOUNDBITE OF JOSH ROUSE'S "BIENVENIDO") Transcript provided by NPR, Copyright NPR.