(Adds additional reporting)
BRASILIA, Sept 22 (Reuters) - The death of a 16-year-old who had a first dose of the Pfizer/BioNTech vaccine against COVID-19 was due to a prior blood clot condition not related to the vaccine, Brazil's health regulator Anvisa said on Wednesday.
Concluding an investigation into the death earlier this month, Anvisa said it was caused by an auto-immune disease suffered by the adolescent. The Pfizer vaccine is the only one approved for minors in Brazil. "It was a characteristic clinical picture of thrombotic thrombocytopenic purpura, an autoimmune disease," the regulator said in a statement.
Thrombotic thrombocytopenic purpura is a rare disorder that causes blood clots to form in small blood vessels throughout the body that can cause serious medical problems if they restrict blood flow to organs such as the brain, kidneys or heart.
Concerns over COVID-19 vaccines and blood clots has prompted investigations by researchers across the world.
The European Commission requested scientific opinion from the European Medicines Agency (EMA) on whether women and young adults were at higher risk of blood clots after vaccination with AstraZeneca's COVID-19 shot. The EMA could not confirm if this was the case.
Brazil's federal government last week sough to halt COVID-19 vaccinations for adolescents while the death was under investigation as a suspected adverse event, but several state governments vowed to press on.
Some 3.5 million Brazilians between the ages of 12 and 17 have already been immunized.
(Reporting by Anthony Boadle Editing by Sonya Hepinstall and Aurora Ellis)