CEO Ed Bastian said that all employees hospitalised for the virus in recent weeks were not fully vaccinated.

The airline said yesterday that it also would stop extending pay protection to unvaccinated workers who contract COVID-19 as of September 30 and will require unvaccinated workers to be tested weekly, beginning September 12, although Delta will cover the cost. They will have to wear masks in all indoor company settings.

Delta stopped short of matching United Airlines, which will require employees to be vaccinated, starting September 27, or face termination. However, the $200 monthly surcharge, which starts in November, may have the same effect.

“This surcharge will be necessary to address the financial risk the decision not to vaccinate is creating for our company,” Bastian said in a memo to employees.

Delta is self-insured and sets premiums for its plans, which UnitedHealthcare administers.

Bastian said that 75 per cent of Delta employees are vaccinated, up from 72 per cent in mid-July. He said the aggressiveness of the leading strain of the virus “means we need to get many more of our people vaccinated, and as close to 100 per cent as possible.”

“I know some of you may be taking a wait-and-see approach or waiting for full [Food and Drug Administration (FDA)] approval,” he told employees. “With this week's announcement that the FDA has granted full approval for the Pfizer vaccine, the time for you to get vaccinated is now.”

A growing number of companies, including Chevron Corporation and drugstore chain CVS, announced they would require workers to get vaccinated after Monday's FDA decision.

United and Delta already require new hires to be vaccinated. Two smaller carriers, Hawaiian and Frontier, have said they will require vaccination or regular testing for current employees. Other major US airlines, including American and Southwest, said yesterday that they encourage employees to get vaccinated but have not required it.

Fuelled by the now-dominant Delta variant of the virus, newly reported cases of COVID-19 in the US have topped 150,000 a day, the highest level since late January. Nationally the rate of increase has slowed, but the variant threatens to overwhelm emergency rooms in parts of the country.

On Tuesday, Governor Brian Kemp of Georgia, where Delta is based, ordered members of the National Guard to 20 hospitals across the state to help deal with a larger surge than the national average.

Southwest, Spirit and Frontier have blamed the rise of the Delta variant for a slowdown in customers booking flights, and US air travel remains down more than 20 per cent from pre-pandemic 2019.

In his message to employees, Bastian referred to the fast-spreading strain of the virus as B.1.617.2, which scientists use to identify its lineage. The Delta CEO's effort to avoid using the more commonly known “Delta variant” did not go unnoticed and B.1.617.2 began trending on Twitter yesterday.