United Airlines (UAL  ) has reported that almost all its workforce has been vaccinated against COVID-19. Around 600 of the company's 67,000 employees remain unvaccinated and un-exempt from the company's mandate.

"This is a historic achievement for our airline and our employees as well as for the customers and communities we serve," said United CEO Scott Kirby and President Brett Hart wrote to employees. "Our rationale for requiring the vaccine for all United's U.S.-based employees was simple - to keep our people safe - and the truth is this: everyone is safer when everyone is vaccinated, and vaccine requirements work."

Some 2,000 workers have applied for the company's religious or medical exemptions and will be placed on (much of it unpaid) leave on October 15, pending ongoing litigation by several employees. The 593 employees that currently remain unvaccinated and un-exempt will be fired from the company. United plans to require all new hires to be vaccinated going forward as well.

United's vaccine efforts began in the weeks before President Joe Biden announced his forthcoming vaccine mandates last month. Other airlines have enacted similar procedures to varying degrees, such as Delta Airlines (DAL  ), which announced that unvaccinated workers would be stuck with a $200 monthly insurance surcharge while similarly requiring all new employees to be vaccinated.

United is far from alone in its hand being forced against unvaccinated employees. Hospitals and nursing homes across the United States find that, while most employees are willing to seek vaccination, there are still minorities of workers who fervently resist inoculation. City governments have been left with whether to fire or reassign unvaccinated police officers, some of whom remain suspended and off-duty.

For the most part, however, the federal vaccine mandate and efforts by businesses to comply have ensured that considerably more of the American workforce is vaccinated. While resignations from mandate requirements have occurred, the mass resignations feared by many don't appear to have materialized.