The U.S. vaccine supply is increasing to 13.5 million doses per week, up from 11 million, and the number of shots distributed through pharmacies will double, White House Press Secretary Jen Psaki said Tuesday.

President Joe Biden’s Covid-19 response coordinator, Jeff Zients, announced the increases to governors in a conference call earlier, Psaki told reporters at a briefing. Two million doses will be delivered to pharmacies this week, she said, up from 1 million. The pharmacy program began Feb. 11.

“This program will expand access in neighborhoods across the country,” she said. “Eventually, as supply increases, more than 40,000 pharmacy locations nationwide will be providing Covid-19 vaccines through this program. This is a critical, critical part of our plan.”

Federal officials also warned governors on Tuesday that extreme winter weather this week may delay vaccine shipments, a spokesman for Governor Larry Hogan of Maryland said on Twitter.

The White House anticipates delays in shipments and deliveries over the next few days and is working to mitigate that, according to an administration official who spoke on condition of anonymity. In particular, the weather is poised to affect a FedEx facility in Memphis, Tennessee, and a UPS facility in Louisville, Kentucky, the official said.

The pace of vaccinations in the U.S. has steadily increased, standing at about 1.7 million doses per day, according to the Bloomberg vaccine tracker.

The increase stems from a rise in shipments, as well as a change in authorization to extract six doses from each vial of Pfizer Inc.’s vaccine, instead of five. Both Pfizer and Moderna Inc.’s vaccines require two doses. Potential authorization of a third vaccine -- such as Johnson & Johnson’s one-dose candidate -- would further fuel the increase.

The U.S. has administered a total of 54.6 million doses so far, with about 11.9% of the population having received at least a first dose, data show.

This article was provided by Bloomberg News.