Just under 900 people received expired doses of a coronavirus vaccine this month at a New York City clinic, health officials said.

The New York City Department of Health and Mental Hygiene is urging the 899 people, who were given Pfizer-BioNTech shots between June 5 and 10 at the former NFL Experience building in Times Square, to get another dose as soon as possible. Experts say the expired doses are not dangerous, but their effectiveness could be in question.

“While there is no safety risk for the patients, the re-administration is being carried out to ensure that the individuals are fully protected,” a spokesman said. “Those patients have received emails, phone calls, and are also being sent letters to make sure they are aware of this situation.”

A representative for the vaccine distributor, ATC Vaccination Services, said in a statement that the company apologizes “for the inconvenience to those receiving the vaccine batch in question.” The statement stressed that there was no danger posed by the doses of the coronavirus vaccine developed by U.S. firm Pfizer with German partner BioNTech, which were considered expired because they spent too much time in a freezer to meet guidelines for full efficacy.

Among those forced to get an additional shot was 15-year-old Dante Swift. The teen told CBS New York that he had been planning to spend time with his friends after receiving what he thought was his second, final dose. Instead, he had to get a third dose.

“I’m feel more sick, definitely more tired,” he told the television station. “My arm hurts a lot more than it did the last time.”

When it comes to his reunion with his friends, he said, “Now we’re probably going to have to wait a little longer.”

As the United States surpasses 175 million vaccine doses distributed, there have been very few reports of incidents like the one in New York City. The Arizona Department of Health Services earlier this month banned a clinic from ordering more vaccines after alleging that it gave out almost 400 expired doses, azfamily.com reported.

And Tennessee health officials launched an investigation in March to determine whether any expired shots were given out. The probe found that no one in the state was given an expired dose, according to the Tennessean.

Panagis Galiatsatos, an assistant professor in the Division of Pulmonary and Critical Care Medicine at Johns Hopkins University School of Medicine, said it’s “hard to say how much efficacy is lost” once a dose is past its expiration date. Because of the negative connotation of the word “expired,” he said, it’s important for the medical community to reassure the public that the shots are not a safety concern.

“We need to do a good job to make sure this negative term doesn’t continue to weaken our ability to have our community members trust the vaccine,” he said.

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