A Chicago-area hospital halted coronavirus vaccinations for its workers after four people had allergic reactions, according to a report.

Only one of the reactions was severe, said officials with the Advocate Condell Medical Center in Libertyville, Ill., where vaccinations are expected to begin again on Sunday.

The other three people who experienced reactions to the historic jab had only mild symptoms which are not unexpected after someone is vaccinated, officials said.

Vaccinations were halted on Friday night.

The Lake County health department said it would closely monitor the situation, noting “some people respond to vaccinations differently than others.”