NEW YORK — Another mutated version of the coronavirus has popped up in New York City, and experts reacted to the the news with a mixture of caution and concern.

The new variant first appeared in the New York area in November and has cropped up in neighboring states, according to researchers at the California Institute of Technology, one of two teams to share their work this week.

But how problematic the variant may be isn’t known yet. Viruses are constantly mutating – or making typos in their genetic code – as they spread and make copies of themselves.

That’s because some genetic tweaks can be worrisome, especially if they help the virus spread more easily, make it more deadly or curb the effectiveness of vaccines.

Scientists use genome sequencing and other research to figure out which are a potential problem.

Two research groups – at Caltech and Columbia University in New York – released papers this week describing their findings about the new variant.

Neither paper has been published or reviewed by other scientists.

Caltech researchers found the variant showed up in about a quarter of the 1,200 virus sequences they looked at this month. The variant has also shown up in New Jersey and Connecticut and has made “isolated appearances across the country,” said CalTech’s Anthony West, a co-author of the paper.

On Thursday, Columbia University researchers released their research that scrutinized about 1,100 virus samples from patients treated at the university’s medical center, dating back to November.

During the second week of February, the new variant was identified in 12 percent of the samples, they reported. They also found patients infected with the mutated virus were more likely to be older and have been hospitalized.

New variants have been showing up throughout the pandemic, but three are considered the most worrisome – they’ve been designated “variants of concern.” They were first detected in Britain, South Africa and Brazil but have spread to other countries.

The one identified in the U.K. late last year has since been found in 45 U.S. states, according to the Centers for Disease Control and Prevention.