When people got reinfected with Covid-19, their odds of ending up in the hospital or dying were 90% lower than an initial Covid-19 infection, according to a new study. The study published Wednesday in the New England Journal of Medicine found that there were few confirmed reinfections among 353,326 people who got Covid-19 in Qatar, and the re-infections were rare and generally mild. The first wave of infections in Qatar struck between March and June of 2020. In the end about 40% of the population had detectable antibodies against Covid-19. The country then had two more waves from January through...