An unvaccinated student who contracted measles recently infected at least 21 people with the virus at a school in New York City.

The outbreak occurred at Yeshiva Kehilath Yakov in Williamsburg last week and comes as the city continues to battle its largest measles flare-up in a decade, The New York Times reported Thursday.

The almost two dozen people who were infected were not vaccinated either, according to the Times, which reported that the student did not exhibit the symptoms of the virus while in class.

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Though public officials and health experts have advised New York City schools against against admitting students who have not been vaccinated for measles, the school reportedly ignored the advice.

But the city's Health Department told the newspaper that the school has since chosen to comply with the emergency measure.

According to the Times, the outbreak has fueled concerns about the number of people in the city’s Orthodox Jewish communities who are not vaccinated.

In the past few months, nearly 200 measles cases have been recorded in the state — 133 in New York City involving people between the ages of 6 months and 59 years — according to the newspaper.

Health Department officials say almost 10,000 people across the city have been vaccinated since fall 2018, and more than 7,000 of those residents reportedly live in Williamsburg and Borough Park, the two areas most affected by the measles outbreak.

The report comes as lawmakers in the United States attempt to tackle what has been considered a growing public health threat as measles outbreaks spread grow across the country.