Norway’s medical regulatory authority reported Thursday that at least 13 people have died from complications after receiving the Pfizer coronavirus vaccine.

Norway began inoculating its citizens with the Pfizer/BioNTech vaccine on December 27, with 67-year-old Svein Andersen becoming the first Norwegian to receive the vaccine, administered at the Ellingsrudhjemmet nursing home where he resides.

Since then, more than 25,000 Norwegians have been vaccinated, and 29 of these have experienced significant side effects, national public broadcaster NRK reported.

Steinar Madsen, the medical director of the Norwegian Medicines Agency — Norway’s regulatory authority for new and existing medicines — noted Thursday that of the total of 29 side effects reported “there are 13 deaths, nine serious side effects, and seven less serious side effects.”

The “serious side effects” included allergic reactions, strong malaise, and severe fever. The seven less serious side effects included “severe pain at the injection site,” NRK said.

A total of 23 deaths have been reported by the Norwegian Medicines Agency in connection with the vaccination but only 13 of these have been comprehensively evaluated so far.

“It seems that some of these patients experience severe side effects in the form of fever and malaise that can lead to a very serious illness becoming a more serious one, which may lead to death,” Madsen said.

All the reported deaths have occurred among frail, elderly patients in nursing homes and all of the deceased are over 80 years old and some are even over 90.

In this context, “frail” means patients with advanced heart conditions, dementia, chronic obstructive pulmonary disease, and other serious diseases, many of which coincide with the most common comorbidities of those who have died from coronavirus worldwide.

At the same time, Madsen emphasized that these cases are rare and that many thousands of equally frail people have been vaccinated without a fatal outcome.

“We are not alarmed by this. It is quite clear that these vaccines have very little risk, with a small exception for the frailest patients,” Dr. Madsen said.

As a result, however, both the National Institute of Public Health and the Norwegian Medicines Agency have changed their coronary vaccination guide with new advice for this group.

“If you are very frail, you should probably not be vaccinated,” Madsen said during a webinar on the coronavirus vaccine for journalists on Thursday.