BETHESDA, Md. (NewsNation Now) — During President Joe Biden’s visit to the National Institutes of Health Viral Pathogenesis Laboratory Thursday he announced that his administration has secured 200 million additional doses, as promised, of the coronavirus vaccine.

“Just this afternoon, we signed the final contracts for 100 million more Moderna and 100 million more Pfizer vaccines,” Biden said. He said the country will have enough supply to vaccinate 300 million Americans by end of July.

Biden said the additional doses would bring the total number of doses to 600 million. The schedule for delivery of the additional doses is unknown at this time.

The pace of injections could increase further if a third coronavirus vaccine from drugmaker Johnson & Johnson receives emergency use authorization from the Food and Drug Administration.

Biden also thanked NIH staff for their hard work and sacrifice on the frontlines.

“All of the heroes on the frontlines remind us who we are. We are America. We never give up. We follow the science and find the answer,” Biden said.

Biden’s NIH visit comes as his administration tackles the COVID-19 crisis on multiple fronts. They have unleashed billions of federal dollars to boost vaccinations and testing and developed a model to deploy more than 10,000 active-duty troops to join even more members of the National Guard to put shots into arms. Mass vaccination sites, supported by federal troops, are set to open in California, Texas and New York in coming weeks.

“We’re at war with this virus,” COVID-19 coordinator Jeff Zients said in an interview with The Associated Press Sunday. “We’re taking every resource and tool the federal government has to battle on every front.”

Biden is already well on pace to exceed his goal of 100 million vaccinations in his first 100 days in office. According to the Centers for Disease Control and Prevention, at least 26 million doses have been administered in Biden’s first three weeks in office.

Much of the improvement in vaccination deliveries so far has been due to long-planned manufacturing ramp-ups, not the actions of the Biden team, aides acknowledge. But with the prospect of a third vaccine receiving approval in coming weeks, they are trying to anticipate and eliminate the next set of bottlenecks, when capacity to deliver injections and demand for vaccines become limiting factors.

Biden’s team has also taken an increased role in determining where each vial of vaccine goes, with an eye on ensuring that lower-income, rural and minority communities are covered, an implicit criticism of how some states have handled their rollouts.

New distributions to community health centers, announced Tuesday, and a 1 million weekly dose pharmacy program being rolled out this week will allow the White House to directly steer vaccines to underserved communities.

The ideas are not without their critics. On a call with the White House on Tuesday, Arkansas Gov. Asa Hutchinson appealed to the administration to work through states rather than alternative distribution avenues, arguing they have excess demand they already can’t meet. Other governors expressed concern that the federal program would upend their own plans to use those health centers to distribute vaccines.

“While governors appreciate the federal partnership, it is important that any increase in manufacturing capacity for vaccines should go to the states for distribution and not duplicated through separate federal programs,” Hutchinson told the AP.

The Associated Press contributed to this report.