CHICAGO (CBS) -- More than two months after upholding Mayor Lori Lightfoot's COVID-19 vaccine mandate for most other city employees, the same arbitrator on Wednesday ruled that Chicago police officers also must comply with the requirement to get fully vaccinated.

Arbitrator George Roumell denied a grievance filed by the Fraternal Order of Police, which represents rank-and-file police officers, and other police unions representing CPD sergeants, lieutenants and captains.

Those were the last unions awaiting an arbitrator's ruling on whether city employees must obey the mayor's executive order requiring them to be fully vaccinated, or face being put on unpaid leave and possibly fired.

"The medical evidence supports the City and Department's vaccine mandate as a reasonable exercise of contractually recognized management rights," Roumell wrote in his ruling upholding the vaccine mandate.

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The ruling sets new deadlines for police officers to get vaccinated. They must get their first dose of the Moderna or Pfizer vaccines, or the single-dose Johnson & Johnson vaccine by March 13, and the second dose of the Moderna or Pfizer vaccines by April 13.

Lightfoot first announced the requirement for all city employees to get vaccinated in August, and gave them until Dec. 31 to comply.

The city's various labor unions sought arbitration on the requirement, and in December Roumell upheld the vaccine mandate for the city's non-police unions, including Chicago Firefighters Union Local 2, AFSCME, SEIU Local 73, IBEW Local 21, Teamsters Local 700, and all Coalition of Unionized Public Employees (COUPE) trade unions. Police officers and supervisors filed their own separate grievance.

Under the earlier arbitration ruling, other union city employees had until Jan. 31 to get fully vaccinated.

Mayor Lightfoot applauded the ruling upholding the vaccine madnate for police officers, saying she hopes it convinces more officers to get their shots.

As of last week, more than 2,800 employees at the Chicago Police Department who had reported their vaccination status had said they are not yet vaccinated, a number Lightfoot acknowledged is concerning.

"Anybody who's unvaccinated in our city concerns me. We are still in the middle of a pandemic," she said. "Of course I have concerns about that, and particularly law enforcement who are on the front lines every day."

The mayor declined to predict how many officers might be threatened with termination if they don't now come into compliance with the vaccination requirement.

The requirement includes the option for any city employee to apply for a religious or medical exemption.