Overnight Health Care: Biden expected to announce vaccine requirement for federal workers | Republican governors revolt against CDC guidance | Pfizer: Third vaccine shot ‘strongly’ boosts immune response against delta

Welcome to Wednesday’s Overnight Health Care. Senate Minority Leader Mitch McConnell is running pro-vaccine ads across Kentucky, using money from his reelection campaign. If you have any tips, email us at nweixel@thehill.com, psullivan@…