Update (1 p.m., Sept. 30): United Airlines on Thursday said the number of employees who faced termination for not meeting the carrier’s vaccination requirement had dropped from 593 to 320. The airline said the decline was largely due to late uploads of employee vaccination cards.

Original story (Sept. 28):

Nearly all of United Airlines’ U.S.-based employees have been vaccinated, the company said Tuesday, touting the success of its policy after becoming the first U.S. carrier to require the vaccine among its workforce.

United’s deadline for meeting the requirement was Monday, and the carrier said Tuesday it has begun the process of terminating 593 employees who declined to be vaccinated and did not apply for a health or religious exemption. The company said less than 3 percent of its roughly 67,000 workforce applied for exemptions, while 1 percent didn’t comply.

“This is a historic achievement for our airline and our employees as well as for the customers and communities we serve,” chief executive Scott Kirby and President Brett Hart wrote in a memo 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.”

Frontier Airlines and Hawaiian Airlines also require employees to be vaccinated, although Frontier offers employees the option of showing proof of a negative coronavirus test. Other carriers, including American Airlines, Alaska Airlines and Delta Air Lines, have encouraged employees to be vaccinated but have not made announcements about a requirement since President Biden this month said he would mandate the shot or weekly testing at companies with more than 100 employees.

A spokesman for Southwest Airlines said its incentive program, which offers a bonus of two days of pay to employees who show proof of vaccination by Nov. 15, remains in effect. As of Nov. 16, only employees who have been fully vaccinated will be eligible for quarantine pay if they are exposed or infected with the virus.

At Delta, where unvaccinated employees will pay a $200 monthly health insurance surcharge beginning Nov. 1, 82 percent of employees have been vaccinated. That’s up from 75 percent at the end of August. The carrier has begun weekly testing for employees who have not been vaccinated.

Derek Dombrowski, a spokesman for JetBlue Airways, said the company is “reviewing details available on President Biden’s recent executive orders to understand how they would apply to JetBlue and our crew members.”

He said the carrier had pop-up vaccination clinics to make it easier for employees to get vaccinated.

At Frontier, employees have until Oct. 1 to provide proof of vaccination. Those who aren’t vaccinated will be required to provide proof of a negative coronavirus test on a regular basis, the airline said. Frontier did not release specific numbers but said in early August a majority of its employees had been vaccinated.

Hawaiian Airlines is requiring employees to be vaccinated by Nov. 1.