Canada has become the first country to authorize use of a plant-based COVID-19 vaccine.

Canadian regulators said Thursday Medicago’s two-dose vaccine can be given to adults ages 18 to 64, but said there’s too little data on the shots in people 65 and older.

The decision was based on a study of 24,000 adults that found the vaccine was 71% effective at preventing COVID-19 — although that was before the omicron variant emerged. Side effects were mild, including fever and fatigue.

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Medicago uses plants as living factories to grow virus-like particles, which mimic the spike protein that coats the coronavirus. The particles are removed from the plants’ leaves and purified. Another ingredient, an immune-boosting chemical called an adjuvant that is made by British partner GlaxoSmithKline, is added to the shots.

While numerous COVID-19 vaccines have been rolled out around the world, global health authorities are looking to additional candidates in hopes of increasing the worldwide supply.

Quebec City-based Medicago is developing plant-based vaccines against multiple other diseases, and the COVID-19 vaccine may help spur more interest in this new method of medical manufacturing.