Twenty-three people died in Norway within days of receiving their first dose of the Pfizer COVID-19 vaccine, with 13 of those deaths — all nursing home patients — apparently related to the side effects of the shots, health officials said.

Common reactions to the vaccine, including fever and nausea, “may have contributed to a fatal outcome in some frail patients,” Sigurd Hortemo, chief physician at the Norwegian Medicines Agency, said in a Friday statement.

All 13 were nursing home patients and at least 80 years old. While officials aren’t expressing serious concern, they are adjusting their guidance on who should receive the vaccine.

The news comes just over a week after officials reported the deaths of just two nursing home residents after they received the Pfizer jab.