NUTLEY, N.J. (CBSNewYork) — More than 86 million U.S. adults are now fully vaccinated, but experts fear that enthusiasm for getting the vaccine could be falling and many Americans may be too eager to take off their masks.

President Joe Biden announced that the United States hit 200 million shots Wednesday, but despite that milestone, doctors are concerned interest for the once-coveted COVID shot is at a crossroads.

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The Kaiser Family Foundation analysis predicts enthusiasm to get vaccinated may peak in the next two to four weeks.

“Unless we can convince more people who are sitting on the sidelines now, we’re not gonna have enough people vaccinated to hit herd immunity,” said Larry Levitt, with the Kaiser Family Foundation.

The pause in distribution of the Johnson & Johnson vaccine is possibly playing into hesitancy, along with a new FDA report that found unsanitary conditions at a plant that produces the J&J vaccine.

COVID VACCINE

Just five states, including New York and New Jersey, make up about 43% of all new infections in the U.S.

Meanwhile, Connecticut is about to drop its outdoor mask mandate. Some have started ditching their mask a long time ago.

“For now, I think I certainly wouldn’t be advocating for people to remove their masks,” said Dr. David Perlin, the chief scientific officer at Hackensack Meridian Health’s Center for Discovery and Innovation.

He says scientists are seeing a big increase in the viral variants from COVID-positive patients.

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“We’re processing several hundred viral islets a day to look for variants,” Perlin said.

About 25% of the samples contain the variant first discovered in South Africa, and Perlin says the U.K. variant is over 50%.

“What is that telling you about how the infection has evolved in New Jersey?” CBS2’s Jessica Layton asked.

“Well, it’s evolved rapidly. If we look at, for example, January, we didn’t see any of the U.K. variant,” Perlin said.

CORONAVIRUS PANDEMIC

It’s worrisome, he says, because as the pace of vaccinations seemingly slows, the virus has a better chance to mutate and spread.

“Really, the best way to knock this virus out is to vaccinate broadly,” he said. “If we do that, then we can get the numbers down low and then, in fact, people can remove their masks and feel comfortable and safe.”

But that’s still likely several months away, considering right now only about a third of Americans are fully vaccinated.

The president is urging companies to offer paid time off so people can go get their shot.

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CBS2’s Jessica Layton contributed to this report.

CBSNewYork Team