By DAVID A. LIEB and GEOFF MULVIHILL
Millions of health care workers across the U.S. must be vaccinated as a result of a mandate from President Joe Biden’s administration that is taking effect. The requirement for many health providers that participate in Medicare or Medicaid takes effect in January for half the states and later in February for the other half. It was part of Biden’s attempt to drive up vaccination rates in private-sector workplaces. But the Supreme Court has blocked a Biden rule that would have required vaccines or regular COVID-19 testing for large employers. Lower courts also have blocked a vaccine requirement for employees of federal contractors.