After Europe was sent reeling following reports of blood clots in some people who received AstraZeneca’s COVID-19 shot, pausing vaccinations, several U.S. medical experts offered differing reactions.

Some oppose the temporary suspensions of vaccinations, arguing it will diminish trust in vaccines, and that the vaccine’s benefits far outweigh the risks of side effects. However, others say European countries did their due diligence in pausing the shots while investigations continue.

Germany, France, Italy and Spain joined the growing list of mostly European countries — starting with Denmark last week — that temporarily halted the use of the AstraZeneca vaccine in recent days to investigate cases of blood clots that occurred after vaccination. Others include Thailand and Congo.

"Once the genie is out of the bottle, and public confidence in vaccines has been diminished, it may be difficult to restore trust," William Moss, director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health, wrote, in part, to Fox News.

While Moss supported the careful investigation of the potential rare risk of coagulation, he argues "vaccinations should have continued."


Europe’s regulator, the European Medicines Agency, and the World Health Organization have both said the benefits of the AstraZeneca jab in preventing COVID-19-related hospitalization and death exceed the risks of potential side effects. These agencies have also noted the number of blood clotting events in vaccinated individuals does not appear to exceed naturally-occurring blood clotting in the general population. EMA plans to convene a safety committee Thursday to assess data and take any necessary action. 

EMA previously noted 30 reported cases of thromboembolic events among nearly 5 million AstraZeneca vaccinations in Europe, as of March 10.

Dr. Anne Liu, an infectious disease physician at Stanford Health Care, says vaccinations should resume as soon as possible if investigations indicate the vaccine is not tied to a heightened risk of blood clotting.


"We don't have much time to lose in this race against the virus and new variants could take advantage of any slowing in vaccination efforts," Liu wrote in part to Fox News. "But I realize that once these concerns are raised, people are quick to believe them and slow to accept evidence dispelling them. It may take time for people to trust the vaccine again, but we don't have a lot of time."

On the contrary, some experts say countries with paused vaccination campaigns were airing on the side of caution.


"The European countries are being very careful about this…" Dr. Abhijit Duggal, critical care physician at Cleveland Clinic, wrote in part. "They are doing their due diligence to make sure that there are no other factors that might be causing certain individuals to perhaps have an increased harm."

Another expert, Dr. Mark Sherwood of the Functional Medical Institute, echoed this, calling the move "prudent" amid "unexpected occurrences."

"The fact that several European countries have paused AstraZeneca shots simply proves that while the research community is doing an amazing job bringing vaccines to market, they are building the plane while flying it, so to speak," Sherwood wrote in an emailed statement. "The public should be open to vaccines, and governments should be equally open about research findings on a day to day basis."

The U.S. has yet to approve the use of AstraZeneca's vaccine. Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said on Wednesday that a regulatory decision on an emergency authorization for the jab could come in April.

The Associated Press contributed to this report.