Five regions in Sweden have temporarily halted their inoculation programmes with one type of vaccine due to issues with the way it was stored during shipping, health officials said.
About 2,100 doses of the Moderna vaccine against Covid-19 were stored at too low a temperature during transport. Some 1,000 of these vaccines have been administered, the officials said.
The Public Health Agency said it would investigate whether the low temperature during shipping had affected the vaccine's properties and whether the people needed to be inoculated again.
"Unfortunately, the distributor made a mistake and transported the vaccine at temperatures that were far too cold, the same level as is needed for Pfizer's vaccine," Anders Tegnell, chief epidemiologist at the public health agency, told Swedish television channel SVT.
Sweden, a member of the European Union, is also using the Pfizer/BioNTech vaccine that has to be stored at extremely low temperatures.
The central-western region of Varmland said it had used 400 doses of the Moderna vaccine that had been stored at too low temperature.
The doses were given to health staff who were being notified about the incident by text message, said physician Ingemar Hallen, who is in charge of infectious disease control in Varmland.
The Swedish pharmacy company that distributes the Moderna vaccines, Apoteket AB, said it was investigating the events.
Overall, Sweden had given some 146,000 vaccinations by January 17, according to the public health agency.
Meanwhile, the agency said on Friday that it has recorded more than 11,000 Covid-19-related deaths.
Sweden, a country of 10.3 million, has now registered 547,000 cases and 11,005 deaths since the pandemic began.