President Joe Biden has once again moved up the timeline for when the United States will have enough COVID-19 vaccine supply for every adult in America, saying Tuesday he believes that goal will be achieved by the end of May. 

The president’s announcement is a marked shift from last week, when Biden and other administration officials said they would have enough doses for 300 million Americans by the end of July.

“This country will have enough vaccine supply for every adult in America by the end of May," Biden said Tuesday from the White House. "The prior administration had contracted for not nearly enough vaccines for adults in America. We rectified that.”

The rapid escalation in the availability of COVID vaccines comes days after the FDA gave emergency use authorization to Johnson & Johnson’s single-dose vaccine regimen. On Tuesday, the White House announced it had invoked the Defense Production Act in order to allow rival drugmaker Merck & Co. to help produce the newly approved coronavirus vaccine in an effort to expand supply more quickly. 

J&J expects to have about 20 million doses available by the end of March, with a total of 100 million doses by the end of June. 

“These efforts will contribute to J&J’s ability to accelerate delivery of their vaccine doses from 100 million doses by the end of June to at or near 100 million doses by the end of May,” the HHS said of the partnership between the two companies in a statement. “In the long term, these actions will ultimately double J&J’s U.S. capacity to produce drug substance and increase the U.S. capacity for fill-finish.”

In another major announcement, Biden said Tuesday he is using his federal authority to direct every state to ensure teachers, school staff, and other educators in K-8 schools receive at least one dose of any available coronavirus vaccine by the end of March. 

"Let's treat in-person learning like the essential service that it is,” Biden said Tuesday. “And that means getting … educators, school staff, childcare workers, and get them vaccinated immediately. They’re essential workers.”

The push will come with support from the federal pharmacy program; teachers and other school workers will be able to go to a number of local pharmacies in order to sign up for their vaccine appointment. While not every K-8 worker will be able to get their appointment in the first week after the president’s mandate, Biden said he hopes his directive will encourage states and providers to prioritize the group. 

States are largely allowed to decide who gets the vaccines when, and many have included teachers in priority groups. As of Biden’s announcement on Tuesday, several states — including Montana, Texas, and Rhode Island — did not include educators or school staff in any vaccine priority group. 

Biden has long pledged to open the majority of K-8 schools across the country by the end of his first 100 days in office, but his administration has offered conflicting guidance on the issue. 

More than 800,000 doses of the J&J vaccine will also be distributed this week to pharmacies to administer in a separate federally-run program that also includes 2.4 million doses of the other two shots. Both figures are expected to steadily increase, as the White House increasingly looks to the capacity of pharmacy chains like CVS and Walgreens to help speed the nation’s mass vaccination campaign.

The Associated Press contributed to this report.