President Biden is expected to sign an executive order on Thursday that requires the vast majority of federal workers and contractors who do business with the government to get the coronavirus vaccine. There will be no weekly testing option.

The new mandate marks an aggressive shift for the president. It’s part of the White House’s new strategy for tackling the pandemic that includes pressuring private businesses, states and schools to put stricter vaccination and testing policies in place to ward off the highly-infectious Delta strain of the virus.

The vaccine requirement for federal employees includes all workers who fall under the purview of the executive branch. That includes White House workers and all federal agencies and members of the armed services — a work force that includes more than four million people. Biden’s executive order does not mandate that those who work for Congress or the federal court system must be vaccinated, according the New York Times.

The spread of the delta variant has caused a sharp spike in COVID-19 infections which has overwhelmed hospitals in some regions and is killing about 1,500 people a day.

More from the Times:

The surge has alarmed Mr. Biden and his top health advisers, who see mass vaccination as the only way to bring the pandemic under control.

Mr. Biden had already pushed federal workers to get vaccinated by announcing that those who refused would have to undergo regular coronavirus testing. But the surge, coupled with last month’s decision by the Food and Drug Administration to grant full approval to the Pfizer-BioNTech vaccine to those 16 and older, has made him decide to take more aggressive steps, eliminating the option of testing, the officials said.

The president is set to give a speech on Thursday afternoon to outline his administration’s plan for tackling the latest surge in the pandemic. The central focus will be on boosting vaccinations. As cases, hospitalizations and deaths continue to climb, the White House and its health advisors see inoculating more Americans as the only way to get the pandemic under control.

Biden’s new approach is a notable change. He’s been hesitant to discuss making vaccines mandatory, mainly because of how politicized it has become due to right-wing misinformation. The FDA approval of the Pfizer vaccine apparently helped the president see it was time to take a firmer approach.

The Pentagon declared almost immediately after the FDA gave the all-clear to the Pfizer shot that all military troops must get the vaccine as part of their service requirements.

Making vaccines mandatory for the massive federal workforce is a big step, but some think President Biden needs to go even further. One suggestion includes making vaccines mandatory for interstate and international travel.

Because vaccines are the province of the states, Biden can’t require all Americans to get vaccinated. But he could use federal funding to encourage states to require their own workers to get vaccinated.

The latest numbers show three-quarters of American adults have taken at least one dose of a coronavirus vaccine. However, only 53 percent of the public is fully vaccinated. Roughly 45 million children under the age of 12 are not yet eligible for vaccination, which means the only way to substantially increase the overall vaccine rate is to convince those adults who are vaccine-resistant. That will require a lot of effort, as polls show that about 14 percent of U.S. citizens say likely will never get vaccinated.

That’s why sources familiar with Biden’s speech told the Times that overarching message he intends to deliver is that the only way for the country to return to some sense of normalcy, is to get as many people vaccinated as possible.