A U.S. Food and Drug Administration official said at a press conference that the allergic reactions had been reported in more than one state, including in Alaska.

Shipments of Pfizer's vaccine are set to arrive at 400 additional hospitals and other distribution sites Tuesday, a day after the nation's death toll surpassed 300,000.

Shipments of precious frozen vials of vaccine made by Pfizer Inc. and its German partner BioNTech began arriving at hospitals around the country Monday.

The prime minister said Monday that the vaccines will be given on a voluntary basis and will be free for citizens and long-term residents.

It comes days after the drugmaker announced that its vaccine appears 95% effective at preventing mild to severe COVID-19 disease in a large, ongoing study.

Although Pfizer's coronavirus vaccine data looks promising, experts say we should remain 'cautious' as the full data has still not been released.

Trudeau said news from Pfizer today is "very encouraging," but warned that it won't bring an immediate resolution to the pandemic resurging across the country.

Pfizer cautioned the initial protection rate might change by the time the study ends. Even revealing such early data is highly unusual.