Now, the Centers for Disease Control and Prevention has stopped investigating breakthrough infections among fully vaccinated people unless they become so sick that they are hospitalized or die. The change means the agency will continue to investigate cases like the death of a vaccinated resident of a nursing home in Kentucky but not the infections of more than 20 other vaccinated residents and employees in the same home who did not require hospitalization. But even relatively mild cases of Covid-19 can lead to persistent long-term health problems, and it will be difficult to know the full scope without tracking mild...
