In Pima County, this means that approximately 2,800 appointments could be postponed between now and Saturday if supplies do not arrive in the next few days.

If you have an appointment to receive a Moderna vaccine at the Tucson Convention Center, Banner-South Kino Stadium or Tucson Medical center, you will be contacted directly if there are any changes to your appointment, officials say.

Pima County officials said Wednesday that sites here administering Pfizer doses have enough supply to maintain operations without interruption, which includes the Tucson Medical Center, Banner-North and the University of Arizona in Pima County.

Sites that administer the Moderna vaccine, however, could face delays in delivery. Meanwhile, Santa Cruz County on Wednesday canceled all appointments through Feb. 21 because of the delayed shipment of the Moderna vaccine. Anyone with an appointment will be notified and rescheduled, the county said.

The state Department of Health Services suggested that people in rural areas and people with appointments for first or second doses of the Moderna vaccine check with providers about availability.

The delay comes as Arizona reported COVID-19 pandemic totals of over 800,000 confirmed cases and more than 15,000 deaths after nearly 13 months since the coronavirus outbreak was first reported in the state.

Across a large swath of the nation, including Deep South states like Georgia and Alabama, the snowy, slippery weather either led to the closing of vaccination sites outright or held up the necessary shipments, with delays expected to continue for days, The Associated Press reported.

In New York, Mayor Bill de Blasio said doses expected this week were delayed by weather elsewhere in the country, forcing the city to hold off making 30,000 to 35,000 vaccination appointments.

One public-health expert said the delays were unacceptable.

“Having vaccine centers take snow days is just going to back things up more than they already are,” said Dr. Amesh Adalja, senior scholar at the Johns Hopkins Center for Health Security. “The virus doesn’t take snow days.”

Adalja said people in charge of vaccination efforts must find ways to be more resilient to weather, “just like mailmen can deliver the mail through sleet or snow.” He suggested clinics use better contingency plans. The goal, he said, must be “a continuous assembly line of vaccines going into people’s arms.”

In Washington, White House COVID-19 coordinator Jeff Zients said that in places where vaccination venues have been closed, like Texas, the government is encouraging sites to increase their hours once they are open, according to The Associated Press.

“We want to make sure that as we’ve lost some time in some states for people to get needles in arms, that our partners do all they can to make up that lost ground,” he said.

The U.S. is vaccinating an average of 1.7 million Americans per day against COVID-19, up from under 1 million a month ago. New figures from the White House show a steady increase in the pace of vaccinations over President 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. The pace of first-dose vaccinations has been largely steady over the past several weeks, hovering around an average of 900,000 shots per day.

Biden is on track to blow past his goal of 100 million shots 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.