Covid-19 antibodies present in about 1 in 5 blood donations from unvaccinated people, according to data from the American Red Cross
Covid-19 vaccine ads expected in next few weeks as part of $250 million Biden administration campaign
One Florida mayor says 'too many people' coming for spring break as US health officials urge vigilance
Teachers want to be back in classrooms, but after a year of Covid-19 it's unclear when all schools will reopen fully
