By Stephanie Stahl

PHILADELPHIA (CBS) — A new U.S. Food and Drug Administration warning about the Johnson & Johnson COVID-19 vaccine has health officials concerned about getting more Americans vaccinated. This comes as COVID cases are once again going up. In New Jersey, there’s been a 38% increase from last week.

This new warning is only for the J&J vaccine, and it’s for a rare side effect. Health officials emphasize that there are no issues with the two main vaccines from Pfizer and Moderna. Still, there’s been a decided drop in people getting vaccinated.

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There were no takers at the Black Doctors COVID-19 Consortium vaccine site in North Philadelphia, which added to the growing concerns about neighborhoods with large numbers of people who are not vaccinated.

“Missed opportunity,” Frederic Bushman with the University of Pennsylvania said. “People are going to get sick that didn’t have to get sick because they didn’t get vaccinated.”

Bushman’s lab at the University of Pennsylvania is tracking the more contagious Delta variant that continues to spread nationally and in the Delaware Valley.

“It’s more likely to cause people to become hospitalized, so it’s quite serious,” Bushman said.

With a renewed emphasis on vaccines in hopes of curbing the Delta variant, there’s a new complication. The FDA is adding a new warning to Johnson & Johnson’s one-dose COVID-19 vaccine.

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The J&J vaccine has been given to nearly 13 million Americans. About 100 developed a rare but serious autoimmune disorder that attacks the nerves called Guillain-Barré.

Still, health officials say the benefits of the vaccine far outweigh the small risks.

“There are very, very low numbers of adverse events, with tens of millions treated, there’s a handful of adverse events,” Bushman said.

Is Bushman concerned the warning will add to more vaccine hesitancy?

“It’s perfectly reasonable that people should want to know if the vaccines are safe,” he said, “and the overwhelming evidence is that they are.”

Johnson & Johnson said, “The chance of having the side effect is very low” and “we strongly support raising awareness of the signs and symptoms of rare events.”

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Also on Tuesday, federal health officials said they’re reviewing suggestions that some people might need a third booster shot of the Pfizer vaccine. At this point, the currently recommended vaccines are effective at guarding against the virus and the variants.

Stephanie Stahl