Twitter is closing its reopened offices in the U.S., as other major technology companies require vaccinations for on-campus employees due to the highly contagious Delta COVID-19 variant.

Google and Facebook announced on Wednesday that all U.S. workers must get vaccinated in order to be able to go to their respective offices. Google also plans to expand its vaccination campaign to other regions in the coming months.

Twitter had started allowing employees to return to their 50% capacity sites in San Francisco and New York after more than 16 months of remote work.

Cases of coronavirus in the U.S. have risen sharply due to the Delta variant, which originated in India but has rapidly spread worldwide and now accounts for more than 80% of COVID-19 cases in the U.S.

Medical experts said Tuesday that Americans who are fully vaccinated against COVID-19 should wear masks in public places in regions where the coronavirus is surging.

San Francisco-based ride-hailing service Lyft Inc, which had already made vaccinations mandatory for employees returning to work, postponed its reopening until February from September.

In addition, streaming giant Netflix Inc has also implemented a policy requiring immunizations for performers and crew in all U.S. productions.

Apple is also restoring masks to most of its U.S. stores, for both customers and employees, regardless of vaccination status.

In addition, Google also announced Wednesday that it will extend its work-from-home policy until October 18 due to the resurgence of COVID-19 cases.

For more information, read the original story in Reuters.