Google’s parent company Alphabet on Monday confirmed that it is delaying the return of workers to its offices until at least September 2021, and is testing the use of “flexible work weeks” in the longer term.

In an email on Sunday to Google staff, Alphabet chief executive Sundar Pichai said the company is exploring a schedule that combines “collaboration days” in the office with days spent working from home.

According to the New York Times, Pichai wrote: “We are testing a hypothesis that a flexible work model will lead to greater productivity, collaboration and well-being.” He noted that no company the size of Alphabet has created a “fully hybrid workforce model.”

Google confirmed on Monday that the e-mail is genuine. The move comes as the US begins a mass vaccination drive that authorities hope will turn the tide in the country worst affected by the coronavirus outbreak, where the national death toll that on Monday surpassed 300,000.

Google and other Silicon Valley firms shifted to remote working early in the pandemic, relying on the internet tools they create to allow employees to do their jobs. Google originally expected that staff would begin to return to their offices in early 2021, but the date has moved as the pandemic has developed in the US.

Facebook chief Mark Zuckerberg has said he expects the transition away from the office to remote working will be a lasting change at the social network, and that it will look to hire employees to work from home, wherever they are located.