...But before more data could be collected to answer these lingering questions, the CDC stopped tracking breakthrough infections that resulted in asymptomatic, mild, or moderate cases. Since May 1, the agency has only reported and investigated coronavirus infections among vaccinated people that resulted in hospitalization or death....That means it's difficult to tell exactly how much of a risk the Delta variant poses to vaccinated people. Researchers still don't know whether Delta makes breakthrough cases more common, or what the typical symptoms of a breakthrough infection caused by Delta look like. As a result, vaccinated people may have a hard time...