United Airlines said that the number of employees facing termination because they aren’t vaccinated against Covid-19 has dropped by almost half since the deadline to get the first shot passed late Monday.

As of Tuesday afternoon, Chicago-based airline had begun the process to fire 593 employees. However, final separation could take several weeks. Only 320 workers were still not vaccinated by Thursday.

United follows the strictest vaccination policy in America. The company informed its 67,000 U.S. workers in August that they had to be immunized against Covid-19 in fall if they wanted to work for the airline. Some 2 000 United employees applied for religious and medical exemptions.

“Our vaccine policy continues to prove requirements work — in less than 48 hours, the number of unvaccinated employees who began the process of being separated from the company has been cut almost in half, dropping from 593 to 320,” United said in a statement.