Administration of the Johnson & Johnson COVID-19 vaccine is on pause in New York City following reports of a severe stroke-like illness linked to low platelet counts.

The Centers for Disease Control and Prevention and the Food and Drug Administration issued the recommendation to pause and will officially review the vaccine.

The cases involved six women between the ages of 18 and 48 years old. One has died, and another is in critical condition. The symptoms showed up about six to 13 days after they had received the vaccine.

"When we saw this pattern and were aware that treatment needed to be individualized, it was of the utmost importance to us to get the word out," said Anne Schuchat, M.D., principal deputy director of the CDC.

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The CDC and FDA say it's not clear if there's any connection to oral contraceptive and stressed that this reaction appears to be rare.

Mayor Bill de Blasio said New York City residents who were scheduled for the Johnson & Johnson vaccine will receive a new appointment with a Moderna or Pfizer vaccine for the foreseeable future.

He also said he doesn't want people to fear the vaccine but rather take this as a positive sign of just how safe it is.

"Certainly is something that makes me sad, given how much progress we've been making lately, but it's also an example of an early warning system working," de Blasio said.