New York City Mayor Bill de Blasio on Monday issued a "preemptive strike," mandating that all private sector employees in the Big Apple be vaccinated against COVID-19 amid the new threat posed by the omicron variant beginning Dec. 27. De Blasio, whose term is set to expire in a matter of weeks, broke the news during an interview on MSNBC’s "Morning Joe" Monday morning. "We’ve got omicron as a new factor, we’ve got the colder weather, which is going to really create additional challenges with the delta variant, we’ve got holiday gatherings," de Blasio said.