The severe winter weather that has slammed most of the nation’s midsection with power outages and closed highways has delayed delivery of 7,800 doses of the Moderna vaccine to Fresno County, community health manager Joe Prado said Thursday.

The doses had not arrived by Thursday morning for distribution, and there is no estimate of when they may arrive, Prado said.

In the meantime, county officials are working with medical providers to provide doses from the county supply to avoid the cancellation of appointments, Prado said.

The Associated Press reported Thursday that severe weather conditions have caused the cancellation of appointments and delayed shipments of COVID-19 vaccine nationwide.

The AP quoted Eamonn Nolan, a Pfizer spokesman, as saying that delays of vaccine shipments should not affect the integrity of Pfizer’s vaccines, which must remain ultra-cold but which are shipped with dry ice in temperature controlled containers that can last 10 days unopened.

Fresno County had been expecting an allotment of 18,000 doses of COVID-19 vaccine this week. With the allotment of 19,000 doses last week — a big increase over 8,000 doses in prior weeks — county officials were hoping to open vaccinations sooner to essential workers such as school staffers if the larger allotments continued.

This week the county started vaccinating residents age 65 and older.