NEW YORK (NYTIMES) - One day after receiving her first dose of Moderna's Covid-19 vaccine, Ms Luz Legaspi, 72, woke up with bruises on her arms and legs, and blisters that bled inside her mouth.
She was hospitalised in New York City that day, Jan 19, with a severe case of immune thrombocytopenia - a lack of platelets, a blood component essential for clotting.
The same condition led to the death in January of Dr Gregory Michael, 56, an obstetrician in Miami Beach whose symptoms appeared three days after he received the Pfizer-BioNTech vaccine.
It is not known whether this blood disorder is related to the Covid-19 vaccines.
More than 31 million people in the United States have received at least one dose, and 36 similar cases had been reported to the government's Vaccine Adverse Event Reporting System, VAERS, by the end of January.
The cases involved either the Pfizer-BioNTech or Moderna vaccine, the only two authorised so far for emergency use in the US.
But the reporting system shows only problems described by healthcare providers or patients after vaccination and does not indicate whether the shots actually caused the problems.
Officials with the Food and Drug Administration and the Centres for Disease Control and Prevention said that they were looking into the reports, but that so far, rates of the condition in vaccinated people did not appear higher than the rates normally found in the US population, so the cases could be coincidental.
In a statement, Pfizer said: "We take reports of adverse events very seriously" and added it was aware of thrombocytopenia cases in vaccine recipients.
Moderna also provided a statement, which did not address the question of the platelet disorder, but said the company "continuously monitors the safety of the Moderna Covid-19 vaccine using all sources of data" and routinely shares safety information with regulators.
Haematologists with expertise in treating immune thrombocytopenia said they suspected that the vaccine did play a role.
But they said cases after vaccination were likely to be exceedingly rare, possibly the result of an unknown predisposition in some people to react to the vaccine by developing an immune response that destroys their platelets.