An Olympic sprinter says she is “upset” at being diagnosed with a rare heart condition after getting her Pfizer booster shot. Swiss athlete Sarah Atcho, who competed in the four-by-100 metres relay at the 2016 Brazil Olympics, revealed in an Instagram post to her 22,000 followers this week that she had been diagnosed with pericarditis, or inflammation of the lining around the heart. Pericarditis and more serious myocarditis, or inflammation of the heart muscle, are known but rare side effects of the Pfizer and Moderna mRNA Covid-19 vaccines. The 26-year-old said she received her booster on December 22 “because I...