“natural immunity.” the study finding that fully vaccinated people are about five times less likely to develop covid, compared to unvaccinated people who previously had the virus. but in new york city, a showdow. the firefighters' union warning of shortages of first responders. >> new york city is going to come to a crisis on monday morning. response times are going to go through the roof. >> reporter: this after thousands of city workers missed a 5:00 deadline today to get vaccinated or go unpaid. but the mayor insists, the mandates are working. >> these numbers are moving constantly. but as of yesterday the total workforce was 88% vaccinated. that's a very high number. >> we know this younger group of children 5 to 11 would get the smaller dose in two shots. how soon could we get that final green light, the yes and then the shots? >> reporter: david, just a