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A COVID vaccine grown in plants measures up

Dr. Naresh Aggarwal talks in April with Jennifer Bain, who volunteered for a study of Medicago's COVID-19 vaccine in Toronto.
Steve Russell/Toronto Star via Getty Images
Dr. Naresh Aggarwal talks in April with Jennifer Bain, who volunteered for a study of Medicago's COVID-19 vaccine in Toronto.

A Canadian biotech firm is reporting positive results from a large study of its COVID-19 vaccine. What makes it unusual is that the key ingredient of the vaccine is grown in plants.

Medicago has already developed an experimental flu vaccine in Nicotiana benthamian, a plant related to tobacco. When the pandemic struck, the company decided to try to make a COVID-19 vaccine.

Now it appears those efforts have succeeded.

"This is an incredible moment for Medicago and for novel vaccine platforms," Medicago CEO and President Takashi Nagao said in a statement.

Vaccines work by showing the immune system something that looks like a virus, but isn't. Doing that allows the immune system to prepare itself in case the real virus shows up.

In Medicago's case, the vaccine look-alike is something called a "viruslike particle" produced in plant cells that were given genetic instructions to make the coronavirus spike protein.

The new results come from a study of more than 24,000 volunteers in six countries. Half got the vaccine, half a placebo. When the study reached approximately 165 cases of COVID-19 among the participants, a review of the results was triggered.

"We had about 74%-78% efficacy to prevent moderate and severe disease," Medicago medical officer Brian Ward told NPR.

The vaccine did slightly worse, closer to 70% efficacy, when looking at all COVID-19 cases, including milder ones.

Medicago vaccine was tested against variants

But there's something important to keep in mind, said Ward. The Medicago vaccine is based on a viruslike particle that looks like the original strain of the virus.

"All of the cases in this study were caused by these new variants," he said.

Most of the cases were either 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.

As for side effects, Ward says, "pretty much everybody gets a sore arm." He says the sore arm is probably due to something called an adjuvant that's added to the vaccine to rev up the immune response. The adjuvant Medicago uses in its vaccine is made by GlaxoSmithKline.

One thing the vaccine's researchers saw very little of was the fever that sometimes accompanies other COVID-19 vaccine shots.

No ultracold freezers required

An advantage of the new vaccine is it does not need special freezers to store it. Standard refrigeration is adequate.

Medicago plans to ask Canadian regulators for authorization to distribute its vaccine. In the meantime, they company is getting supplies of the vaccine ready.

"We have commercial lots being filled into vials as we speak," Ward says.

But manufacturing capacity is an issue. Right now, the plants making the viruslike particles are grown in North Carolina. Ward says he's confident that the company will be able to supply the 76 million doses it already promised to the Canadian government. And he says the company is building a new facility with much greater capacity.

"And if we're still stuck with a COVID problem in by late 2023, then our major global facility will come on line in Quebec City," Ward says.

Unfortunately, the world may indeed still be stuck with COVID-19 then.

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Joe Palca is a science correspondent for NPR. Since joining NPR in 1992, Palca has covered a range of science topics — everything from biomedical research to astronomy. He is currently focused on the eponymous series, "Joe's Big Idea." Stories in the series explore the minds and motivations of scientists and inventors. Palca is also the founder of NPR Scicommers – A science communication collective.