A Facebook spokesperson confirmed this to Business Insider. "Our US offices remain closed and we don't expect them to open before the COVID-19 vaccines are widely available. At yesterday's company Q&A, Mark said that at this point, based on what we know, we don't think it will be necessary to require a vaccine for employees to return to work. He also said he's confident in the vaccine and looks forward to getting one himself," the spokesperson said.

The spokesperson stressed that employees won't be asked to return to the office until July 2021. They added:"Once we return to the office, we will have a number of protocols in place that we expect to include testing, social distancing, wearing masks and other best practices. We continue to work with many experts to define a plan that prioritizes everyone's health and safety."

Zuckerberg has publicly endorsed the rollout of a COVID-19 vaccine. He interviewed Dr. Anthony Fauci about the vaccine during a Facebook livestream. He also said Facebook has already made contact with the incoming Biden administration to ask how it can help with the COVID-19 response.

Pfizer and BioNTech's vaccine started rolling out in the UK this week, and a committee of 20 experts in the US voted in favor of emergency authorization. It's now up to the FDA to decide whether to go ahead and give it emergency authorization.