Moderna Inc. fell in premarket trading Monday after the Food and Drug Administration said in a memo late last week it would place new restrictions on which vaccines hit the market.

Vinay Prasad, a top FDA official, blamed Covid shots for playing a role in the deaths of 10 children in the memo he sent to agency staff on Friday, which was widely reported in media outlets and on social media. He said the FDA will require vaccine makers to perform additional tests to get their shots approved as a result of the safety concerns.

Moderna, which produces Covid shots, fell 3.8% at 8:09 a.m. in New York on Monday, before the start of regular trading. Other vaccine makers also dipped. Pfizer Inc. slid 0.4%, BioNTech SE and Novavax Inc. fell about 2% while Vaxcyte Inc. declined 12%.

The decision ha

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