Norway has launched an investigation into the deaths of 23 people -- all of them elderly citizens living in nursing homes -- after they were inoculated with the first dose of the COVID-19 mRNA vaccine from Pfizer/BioNTech.

It's unclear at this time if all the deaths are directly linked to the vaccine. Norwegian health officials pointed out some 400 senior citizens die each week from various causes in Norway's nursing home population.

"We are not alarmed by this," said Dr. Steinar Madsen, medical director of the Norwegian Medicines Agency.

"It is quite clear that these vaccines have very little risk, with a small exception for the frailest patients. Doctors must now carefully consider who should be vaccinated," he noted.

"Those who are very frail and at the very end of life can be vaccinated after an individual assessment."

Madsen said all the deaths would be thoroughly evaluated by the agency to determine if these incidents are related to the vaccine.

"The Norwegian government will also consider adjusting their vaccination instructions to take the patients' health into more consideration," he said.

Of the 23 deaths, 13 were very elderly nursing home patients at least 80 years old, said officials at the Norwegian Medicines Agency. All the 13 persons that died had exhibited the serious side effects associated with the vaccine.

The agency also said 16 other people who suffered serious side effects had survived. Severe side effects include allergic reactions, strong discomfort, and severe fever.

Of the 29 hit by serious side effects, 21 were women, and eight were men. Seven other people had less serious side effects, such as severe pain at the injection site.

A Pfizer spokeswoman said the company is "aware of reported deaths" following the administration of the vaccine in Norway. Pfizer is now working with the Norwegian Medicines Agency to gather all the relevant information.

"Norwegian authorities have prioritized the immunization of residents in nursing homes, most of whom are very elderly with underlying medical conditions and some which are terminally ill," said the spokeswoman . "(The Norwegian Medicine Agency confirms) the number of incidents so far is not alarming, and in line with expectations."

Norway has seen 57,734 confirmed cases of COVID-19 and 517 deaths since the first case was confirmed in February 2020, based on data from the U.S. Centers for Disease Control and Prevention (CDC).

Norway is also using vaccines by Moderna, Inc., and AstraZeneca in a ramped-up vaccination campaign. It intends to vaccinate 1.3 million Norwegians in risk groups such as the elderly in this first quarter. The number to be vaccinated accounts for 23% of Norway's population.