SAN FRANCISCO, Calif. (KRON) — Health officials are looking more closely into the deaths of nearly two dozen people after receiving their first dose of the Pfizer COVID-19 vaccine in Norway.

A total 23 people died within days of receiving their first dose, the Norwegian Medicines Agency announced in a statement.

Of those deaths, 13 were nursing home patients who were at least 80-years-old and were apparently related to the side effects of the vaccinations, according to health officials.

Dr. Sigurd Hortemo, chief physician at the Norwegian Medicines Agency, said in the press release that common side effects like fever and nausea “may have contributed to a fatal outcome in some frail patients.”

The Norwegian Medicines Agency says it cannot rule out side effects of the vaccine contributing to serious course and fatal outcome in patients with serve underlying disease.

As a result, the COVID-19 vaccination guide has been updated with more detailed advice on vaccinating the elderly.

The Norwegian Medicines Agency and the National Institute of Public Health will assess all reports of suspected reactions.

The Pfizer vaccine requires two doses separated by 21 days. It must be stored in an ultra-cold freezer, thermal shipping container, or refrigerator.

Amid a vaccine rollout that has offered real hope for some countries, the global death toll from COVID-19 topped 2 million Friday.

All told, over 35 million doses of various COVID-19 vaccines have been administered around the world, according to the University of Oxford.