Vaccines that protect against severe illness, death and lingering long Covid symptoms from a coronavirus infection were linked to small increases in neurological, blood, and heart-related conditions in the largest global vaccine safety study to date. The rare events " identified early in the pandemic " included a higher risk of heart-related inflammation from mRNA shots made by Pfizer Inc., BioNTech SE, and Moderna Inc., and an increased risk of a type of blood clot in the brain after immunization with viral-vector vaccines such as the one developed by the University of Oxford and made by AstraZeneca Plc. The viral-vector jabs were also tied to an increased risk of Guillain-Barre syndrome, a neurological disorder in which the immune system mistakenly attacks the peripheral nervous system. More than 13.5 billion doses of Covid vaccines have been administered globally over the past three years. Still, a small proportion of people immunized were injured by the shots, stoking debate about their benefits versus harms. The new research, by the Global Vaccine Data Network, was published in the journal Vaccine last week. Exercise intolerance, excessive fatigue, numbness and "brain fog" were among common symptoms identified in more than 240 adults experiencing chronic post-vaccination syndrome in a separate study conducted by the Yale School of Medicine. The cause of the syndrome isn't yet known, and it has no diagnostic tests or proven remedies.