* Philadelphia Imposes Curfew Amid Unrest Over Black Man's Killing

**The United States hit a record seven-day average of new Covid-19 cases last week, logging more than 83,000 new infections on both Friday and Saturday. Experts will know by early December whether a potential coronavirus vaccine is safe and effective, but there probably won't be widespread availability until later next year, Dr. Anthony Fauci, the top US infectious disease expert, said Sunday.