Norway is investigating the death of two nursing home residents who died after receiving doses of the Pfizer and BioNTech coronavirus vaccine, WION reports.

It comes after a paediatric surgery assistant in Porto was found dead two days after receiving jabs of Pfizer's vaccine.

Medical Director of Norwegian Medicines Agency Steiner Madsen said in a statement: "We have to assess whether the vaccine is the cause of death, or if it is a coincidence that it happened soon after vaccination."

The agency along with Norway's National Institute of Public Health are looking into cause the deaths.

Madsen also added that as people of advanced age are receiving the coronavirus vaccine first it is entirely possible that the deaths could be coincidental.

After Pfizer's claim that the COVID-19 vaccine is more than 90 per cent effective based on initial trial results, a few volunteers said that they suffered side effects comparable to a flu jab, with one comparing them to "a severe hangover".