U.S. COVID-19 vaccine rollout has been hindered by power outages amid the ongoing winter storms in much of the country, with nearly all states experiencing shipment delays.
U.S. government vaccine distribution partners "have all faced challenges as workers have been snowed in and unable to get to work to package and ship the vaccines," said Andy Slavitt, White House senior adviser for COVID-19 response, on Friday.
The country has a backlog of six million vaccine doses due to storm weather, according to the White House.
More than 2,000 COVID-19 vaccination sites have been affected, slowing the pace of administering doses.
Some vaccines were sitting "safe and sound" in factories and hubs, and approximately 1.4 million doses were being transported Friday, according to Slavitt.
UPS and FedEx will be making Saturday deliveries, and all backlogged doses would be delivered "within the next week," he said.
Slavitt also announced that the federal administration is working with Florida and Pennsylvania to open five additional vaccination centers.
California, the most populous U.S. state hit hard by the pandemic, has witnessed severe delay of vaccine shipments, leading to the cancellation of vaccination appointments.
Los Angeles has postponed more COVID-19 vaccination appointments originally scheduled for Saturday as vaccine shipments remain mired in transit.
Local officials pushed back 12,500 appointments scheduled Friday because of supply disruptions.
"Notifications will be sent by text, email or phone as soon as we confirm the arrival of new doses," Los Angeles Mayor Eric Garcetti tweeted.
U.S. President Joe Biden on Friday visited Pfizer's COVID-19 vaccine manufacturing facility in Michigan amid vaccine delays.
Biden said he was confident the United States would surpass his goal of administering 100 million coronavirus vaccine shots into the arms of Americans during his first 100 days in office, and predicted that the nation would be "approaching normalcy by the end of this year."
About 59.58 million doses have been administered as of Friday, according to the U.S. Centers for Disease Control and Prevention.