DeSantis says the answer is Regeneron treatment. As the Associated Press reported on Tuesday, one of DeSantis' top donors has a large financial stake in the success of Regeneron:

Citadel, a Chicago-based hedge fund, has $15.9 million in shares of Regeneron Pharmaceuticals as well as options to buy its stock, according to filings with the U.S. Securities and Exchange Commission. Citadel CEO Ken Griffin has donated $10.75 million to a political committee that supports DeSantis -- $5.75 million in 2018 and $5 million last April.

DeSantis has held four events promoting Regeneron in one week. He has not held an event specifically promoting vaccines, however, since May, when he announced his vaccine passport ban.