No link has been established between Pfizer-BioNTech's COVID-19 vaccine and post-vaccination deaths in Norway, according to the country's health authorities.

Since the start of Norway's vaccination campaign at the end of December, the country has registered 33 deaths among elderly people who have received their first dose.

Of the 13 cases analysed in detail so far, "they are people of advanced age, are frail and have serious illnesses, all of them," the director of the Norwegian Institute of Public Health Camilla Stoltenberg told reporters.

"When it comes to causes there hasn't been any analysis done yet," she added.

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"It is important to remember that on average about 45 people die every day at nursing homes in Norway, so it's not given that this represents any excess mortality or that they are related to the vaccines," she said.

After the reports of deaths, Norway has nonetheless stressed that doctors should consider case-by-case whether patients who are frail or terminally ill should receive the vaccine, as is recommended in some other countries.

"It's not impossible that some of those who have gotten the vaccine are so frail that maybe you should have reconsidered and not given them the vaccine, because they are so sick that they might have become worse from the normal side effects as the body reacts and builds up immunity," Stoltenberg said.

Side effects of vaccine 

The Norwegian Medicines Agency said last week that normal side effects from messenger RNA vaccines, such as fever and nausea, "may have contributed to a fatal outcome in some frail patients."

A number of countries, including Norway's fellow Nordic nations Denmark, Finland, Iceland and Sweden, have reported post-vaccination deaths but no direct links to the vaccine have been established.

Pfizer and BioNTech said that they were "working with the Norwegian Medicines Agency to gather all the relevant information."

They recalled that Norway's vaccination campaign started with the elderly living in care homes, "most of whom are very elderly with underlying medical conditions and some of which are terminally ill."

More than 48,000 people have been vaccinated in Norway so far.