Health authorities are investigating the case of a Florida doctor who died from an unusually severe blood disorder 16 days after receiving the Pfizer coronavirus vaccine. Dr. Gregory Michael, a 56-year-old obstetrician and gynecologist in Miami Beach, received the vaccine at Mount Sinai Medical Center on Dec. 18 and died 16 days later from a brain hemorrhage, his wife, Heidi Neckelmann, wrote. Shortly after receiving the vaccine, Dr. Michael developed an extremely serious form of a condition known as acute immune thrombocytopenia, which prevented his blood from clotting properly. About nine million people in the United States have received at least one shot of either the Pfizer or Moderna coronavirus vaccine, the two authorized in the United States. So far, serious problems reported were 29 cases of anaphylaxis, a severe allergic reaction. Dr. Jerry L. Spivak, an expert on blood disorders at Johns Hopkins University, who was not involved in Dr. Michael's care, said that based on Ms. Neckelmann's description, "I think it is a medical certainty that the vaccine was related." "This is going to be very rare," said Dr. Spivak, an emeritus professor of medicine. But he added, "It happened and it could happen again." Dr. Paul Offit, an expert in vaccines and infectious diseases ... said that the measles vaccine and measles itself have been known to cause this same clotting problem, but it is usually transient and not serious. It occurs in about one of every 25,000 measles shots