Update (1300ET): Moderna has issued a statement addressing the disturbing number of severe reactions to a batch of its COVID vaccine:

Moderna acknowledges receiving a report from the California Department of Public Health (CDPH) that several individuals at one vaccination center in San Diego were treated for possible allergic reactions after vaccination from one lot of Moderna's COVID-19 Vaccine. The Company is fully cooperating with CDPH in investigating these reported adverse events. Consistent with the statement from CDPH, at this point

Moderna is unaware of comparable clusters of adverse events from other vaccination centers which may have administered vaccines from the same lot, or from other Moderna lots. Moderna confirmed that a total of 1,272,200 doses were produced in batch number 041L20A, with nearly a million doses (964,900) already distributed to approximately 1,700 vaccination sites in 37 states. According to CDPH, that includes more than 330,000 doses from this lot distributed to 287 providers across the state of California. A total of 307,300 doses remain in storage and not yet distributed.

While Moderna said it does not know how many doses may have ended up in arms of people, it did report that the lot was shipped between January 4th and January 8th, and thus it expects that a significant portion of the distributed doses have been already used. This investigation is still ongoing and Moderna is working closely with FDA and CDC to understand the clinical cases and whether the broad pause in use of the lot is warranted.

Moderna's share price is down around 4% after this news...