WASHINGTON (NewsNation Now) — Severe winter weather this week that left many Americans without power, water or shelter has also caused a backlog of 6 million COVID-19 vaccine doses, a White House official announced Friday.

White House coronavirus adviser Andy Slavitt said vaccine delivery to all 50 states has been impacted by the storms that covered roads with ice and snow and led utilities to use rolling blackouts to ease strained power grids.

“The 6 million doses represents about three days of delayed shipping, and many states have been able to cover this delay with existing inventory,” Slavitt said during a White House COVID-19 response team briefing Friday.

Road closures and more than 2,000 vaccine sites located in areas with power outages continue to hold up deliveries, according to Slavitt.

So far, 1.4 million doses are in transit Friday, Slavitt said. The Biden administration anticipates all backlogged doses will be delivered within the next week, with most in the coming days.

The White House COVID-19 response team also announced five additional vaccination centers, one in Pennsylvania and four in Florida.

The news came ahead of President Joe Biden’s visit to a Pizer manufacturing facility in Michigan.

At the plant, Biden walked through an area called the “freezer farm,” which houses some 350 ultra-cold freezers, each capable of storing 360,000 doses of the Pfizer-BioNtech vaccine. 

Double-masked, the president stopped to talk with some of the workers, but it was difficult for reporters on the trip to hear what was said.

“All of you here are doing some of the most important work in this facility, right here, that can be done,” Biden said in an address to plant workers.

“Take the vaccine when it’s your turn and available. That’s how to beat this pandemic,” he said.

Speaking after Biden’s visit, Pfizer CEO Albert Bourla said on Friday that the drugmaker expects to be able to double the weekly number of doses of its COVID-19 vaccine it will supply to the United States in the next few weeks.

“We have improved our processes to double the batch size and increase yield and we have deployed more efficient lab test methods to reduce release times,” Bourla said in his remarks.

President Biden announced last week that the U.S. will have enough supply of the coronavirus vaccine by the end of the summer to inoculate 300 million people and remains focused for now on making sure every American is inoculated, administration officials say.

Pfizer has said it will provide the U.S. government with 100 million doses by the end of March and another 100 million by the end of May. It has promised the full 300 million doses by the end of July.

Last year, President Biden announced a vaccination goal of 100 million coronavirus shots in his first 100 days in office. New figures from the White House show the steady increase in the pace of vaccinations over President Joe Biden’s first month in office.

Much of the increase, according to data from the Centers for Disease Control and Prevention, comes from people receiving their second dose of the approved vaccines from Moderna and Pfizer.

Biden is on track to beat his goal of 100 million injections in his first 100 days in office — though the pace must pick up even further to meet his plans to vaccinate nearly all adults by the end of the summer.

More than 73 million vaccine doses have been distributed across the United States, with more than 57.7 million doses administered, according to the CDC.

The Biden administration has been working to increase the number of doses it sends out to states, cities and pharmacies every week, but Dr. Anthony Fauci, the nation’s top infectious diseases expert, said on Tuesday that demand far outpaced supply at the moment.

The White House COVID-19 team announced earlier this month that the administration would use the Defense Production Act to help Pfizer get additional equipment fast so that it could keep ramping up production. Biden was expected to discuss that initiative – which officials say is starting to pay dividends – with Pfizer executives during his tour.

Reuters contributed to this report. Reporting by Andrea Shalal and Michael Erman.