A New York City health care worker had a "significant" allergic reaction after receiving the first dose of the coronavirus vaccine, city health officials said Wednesday morning.

The health care worker was treated and is said to be in stable condition. To date, more than 30,000 vaccinations have been administered in the city.

This is the first known adverse reaction reported in New York City. It was not immediately clear if the worker had a history of significant allergic reactions.

"Vaccines do have side effects and allergic reactions – while uncommon – are known to occur," the NYC Department of Health said in an email to reporters. "We also know that based on clinical trials and reports of adverse effects in other jurisdictions, reactions such as these are rare but have been reported with the Pfizer vaccine."

The Department of Health declined to provide any further details at this time, including when the reaction occurred.

During a press conference at City Hall, Dr. Dave Chokshi, the city's health commissioner, stressed that allergic reactions to the vaccine, also known as anaphylaxis, were considered rare.

"These vaccines are very safe overall," he said.

Chokshi said that those with food or seasonal allergies should take the vaccine, while those with a significant history should consult their doctor first.

Dr. Jay Varma, one of the city's top health advisers, said that the public needs to keep these incidents in perspective.

A small risk of allergic reactions "needs to be balanced against the known risks of this infection."

"I know which side I personally fall on," Varma added, saying that both he and his wife, who is a pediatrician, were confident in the safety of the vaccine.

Around 200 New York City residents are being admitted daily to hospitals for coronavirus. Since the start of the pandemic, more than 24,700 people in the five boroughs have died from the disease.

Both the Pfizer and Moderna vaccine were authorized after showing high efficacy and safety levels in large randomized trials. None of the trial participants had severe allergic reactions, but people with a history of anaphylaxis were excluded.

Dr. Denis Nash, an epidemiology professor at CUNY, said health officials need to collect more data and closely monitor patients receiving the vaccine.

"Ultimately, the goal will be to understand how rare or common it is, and which things may predispose people to this kind of outcome," he said.

The National Health Institute is currently putting together a study to figure out why people may have severe allergic reactions to the vaccine.

Last week, two health care workers in Alaska required treatment for allergic reactions shortly after receiving Pfizer's coronavirus vaccine, marking the first known adverse reactions in the United States. One of them was admitted into an intensive care unit.

As of December 18th, six people in the U.S. had been identified as having severe allergic reaction to Pfizer's coronavirus vaccine.

More than half a million Americans have received the first dose of the coronavirus vaccine.

According to Science Magazine, anaphylactic reactions “can occur with any vaccine, but are usually extremely rare—about one per 1 million doses.”

Dr. Jessica Justman, an associate professor of epidemiology at Columbia School of Public Health, said that according to some published scientific articles, the rate of a severe allergic reaction after receiving a flu vaccine is about one to two in a million.

She said she believed the latest cases of allergic reactions to the coronavirus vaccine were already being closely studied by experts, but she added that transparency and communication are "always important in public health situations and help maintain the trust of the public."

The Centers for Disease Control and Prevention guidelines say people given the vaccine must be kept under observation for at least 15 minutes.

The CDC also advises that anyone who has had a severe allergic reaction to any ingredient in the Pfizer-BioNTech vaccine should not get vaccinated.