■ A closer look at side effects of the vaccine,

Like all new drugs, the vaccines that have been authorized to protect against COVID19 come with some safety concerns and side effects.

Many people who have received the first two Western shots, one from Pfizer Inc. and Biontech SE, and another from Moderna Inc., have experienced fever, headache and pain at the site of the injection.

More worrisome, Norway has reported deaths among elderly people with serious underlying health conditions following administration of the Pfizer-biontech vaccine — possibly linked to those side effects.

1. What’s known about the deaths?

Thirty-three were reported in mid-january among 42,000 people given the Pfizer-biontech vaccine in Norway. Those who died were all in the “75 years +” bracket and included terminally ill patients. Health authorities in Norway say there’s no evidence of a direct link between the 33 cases and the vaccine they received. Sigurd Hortemo, chief physician of the Norwegian Medicines Agency, said he can’t rule out that common adverse reactions may be lifethreatening in patients with severe underlying health problems.

2. Have there been deaths elsewhere?

In Germany, where more than 800,000 people received their first of two doses of the Pfizerbiontech vaccine, the Paul Ehrlich Institute investigated at least seven cases of elderly people dying after vaccination. It said the deaths were probably due to underlying diseases, not the inoculation.

3. What is known about risks in older people?

Not a great deal. It’s possible that common adverse reactions to vaccines that aren’t dangerous in fitter patients may aggravate underlying disease in the elderly, said Steinar Madsen, the Norwegian agency’s medical director.

4. What is being done in response to the deaths?

The Norwegian Institute of Public Health has updated its COVID-19 vaccination guide on vaccinating the elderly who are frail.“we are now asking for doctors to continue with the vaccination, but to carry out extra evaluation of very sick people whose underlying condition might be aggravated by it,” Madsen said.

5. What other serious reactions have there been?

Sometimes the effort to repel an infection can itself be damaging. In rare cases, it can produce inflammation and swelling of tissues in a serious allergic reaction called anaphylaxis. It can be fatal if, for example, the person’s airway swells shut, though deaths are rare.

6. Where have coronavirus vaccines triggered cases?

The U.S. Centers for Disease Control and Prevention said 21 cases of anaphylaxis linked to the Pfizer-biontech vaccine had been confirmed in the country as of Dec. 23. Of those, 17 had a history of allergies, and seven had a history of anaphylaxis. Two cases in the U.K. and one in Israel have been reported.

7. Has anaphylaxis been connected to vaccines before?

Yes. Such reactions occur about 1.3 times per million doses of flu vaccine administered. For the Pfizer-biontech coronavirus vaccine, according to the CDC, the rate is 11.1 per million doses. The agency said the risk surrounding the vaccine is less than the risk of getting a severe case of COVID-19.

8. Do we know what is causing the reactions?

The two leading candidates are polyethylene glycol — a chemical found in many foods, cosmetics and medications — and lipid nanoparticles that encapsulate the messenger RNA, a genetic component in the vaccines. Once a cause has been narrowed, it may be possible to make coronavirus vaccines even safer.