A "fit and healthy" man died from a blood clot three weeks after getting his Covid vaccine, an inquest has heard.
Jack Last, an engineer from Stowmarket in Suffolk, developed a "throbbing headache" six days after receiving the AstraZeneca jab in March 2021.
He first visited A&E on 9 April but doctors believed he was suffering from a migraine and that the risk of a vaccine-induced clot was low.
Concerns had been raised about a possible link between the AstraZeneca vaccine and a rare blood-clotting problem.
It led the Medicines and Healthcare products Regulatory Agency (MHRA) to advise that people under 40 should only be given the Pfizer or Moderna jabs where possible - but those guidelines were not issued until May 2021.
As the inquest into his death opened at Suffolk Coroner's Court, it heard 27-year-old Mr Last had developed a blood clot on his brain.
He died at Addenbrooke's Hospital in Cambridge on 20 April.
In a statement, Mr Last's parents told the court they believed "he had a strong chance of survival if he had been given the right treatment when he walked into the hospital".
"That chance was taken away," they said, adding: "We had no medical knowledge. We put our faith in the NHS to help Jack."
The inquest heard from William Petchey, the first consultant to see Mr Last when he was admitted to West Suffolk Hospital on 9 April.
He said the patient's "vital observations were unremarkable" and, although he was concerned about a vaccine-induced thrombosis, thought "the probability was low".
Guidelines from the MHRA maintain that the risk of blood clotting is very low and that any risks of the Oxford/ AstraZeneca vaccine continue to outweigh the risks for the vast majority of people.
Dr Petchey said he asked a junior doctor to book a scan called a CT venogram but, because the radiographer did not have the "technical expertise" needed, a regular CT was carried out instead.
The hospital has since run a recruitment programme to ensure those scans can be performed whenever needed.
Martin Besser, an on-call haematologist at Addenbrooke's Hospital, said doctors faced a "difficult decision" as to how to treat him.
He added: "On one side, there was the possibility of thrombosis and on the other side there was a possibility of a bleed.
"You're trying at every step to do the least damaging thing for the patient."
Following Mr Last's death, his sister Jasmine paid tribute to her "amazing brother" who "made everyone happy".
She added: "Everything you did with Jack was so much better just because he was there."
The inquest is expected to conclude on Wednesday.
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