President Biden grew heated Thursday while defending his administration's flip-flop on whether vaccinated Americans need to wear masks. 

Fox News' Peter Doocy pressed Biden about his administration's reversal, pointing to the president's statement in May that, "If you are fully vaccinated, you no longer need to wear a mask." 

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"In May you made it seem like the vaccine was the ticket to losing the mask forever," Doocy pointed out.

President Biden gets heated while answering a question from Fox News' Peter Doocy.  ( AP Photo/Susan Walsh)

"That was true at the time," Biden shouted. "Because I thought there were people that were going to understand that getting vaccinated made a dramatic difference and what happened was the new variant came along, they didn’t get vaccinated, it spread more rapidly, and more people were getting sick."

"That’s the difference," Biden added before walking away. 

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During the press conference, Biden laid out a plan to incentivize Americans to get vaccinated including a call for $100 payments from the government to people who choose to get vaccinated. 

Biden will also push for businesses to offer paid time off to employees in order to get them vaccinated and will require all federal workers to be vaccinated or face rigorous testing and social distancing requirements.

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"It's time to impose requirements on key groups to make sure they are vaccinated," Biden said. 

"Every federal government employee will be asked to attest to their vaccination status. Anyone who does not attest will be required to mask no matter where they work and test 1-2 times a week, socially distance, and will generally not be allowed to travel for work."