Covid-19 Vaccine Live Updates: Mississippi Opens Eligibility, Italy Lockdown and

Germany, France and Italy temporarily suspended the use of AstraZeneca’s Covid-19 vaccine on Monday, joining a growing list of nations that paused use of the vaccine in recent days over concerns that it might be tied to blood clots.

Leading public health agencies, including the World Health Organization, say that millions of people have received the vaccine without experiencing blood clotting issues, and they caution that experts have not found a causative link between the vaccine and the conditions. The company has also defended the vaccine as safe, amid the flurry of suspensions.

The safety scare is a setback for AstraZeneca’s vaccine, which has already struggled with a perception that it is a less desirable shot because it had a lower overall efficacy rate in clinical trials than some others. There is, however, extensive data showing that the vaccine is safe and effective, and especially good at preventing severe illness and death. In many places across the world, it is the only shot available.

Public health experts expect medical conditions to turn up by chance in some people after they get any vaccine. In the vast majority of cases such illnesses have nothing to do with the shots.

Scientists also worry that suspensions could feed vaccine hesitancy at a time when some European countries are entering a third wave of the virus, and the world is in a race to inoculate as many people as possible, as dangerous virus variants proliferate.

The European Medicines Agency, the W.H.O. and other regulators are investigating whether there is evidence of any link between the vaccine and blood clots.

On Monday, the E.M.A. reiterated its position that the benefit of the AstraZeneca vaccine outweighs the risk posed by possible side effects. And officials with the W.H.O. emphasized that the regulators’ investigations are precautionary and cover the batches of vaccines produced in Europe — not the ones made in South Korean and Indian facilities.

“While we need to continue to be very closely monitoring this, we do not want people to panic,” Dr. Soumya Swaminathan, chief scientist at the W.H.O., said on Monday. For the time being, she said, the W.H.O. advises countries to continue vaccinating citizens with the AstraZeneca vaccine.

Tedros Adhanom Ghebreyesus, the director general of the W.H.O., added that reviews of vaccine side effects are not unusual.

“It’s routine practice to investigate them, and it shows that the surveillance system works and that effective controls are in place,” he said on Monday.

AstraZeneca defended its product on Sunday, saying that the company is continually monitoring its safety.

“Around 17 million people in the E.U. and U.K. have now received our vaccine, and the number of cases of blood clots reported in this group is lower than the hundreds of cases that would be expected among the general population,” said Ann Taylor, the company’s chief medical officer.

In France, President Emmanuel Macron said on Monday that the…