By Alison Sider and Peter Loftus

United Airlines Holdings Inc. on Friday began operating charter flights to position doses of Pfizer Inc.'s Covid-19 vaccine for quick distribution if the shots are approved by regulators, according to people familiar with the matter.

The initial flights are one link in a vast global supply chain being assembled to tackle the logistical challenge of distributing Covid-19 vaccines. Pfizer has been laying the groundwork to move quickly if it gets approval from the Food and Drug Administration and other regulators around the world.

Pfizer's distribution plan also includes refrigerated storage sites at the drugmaker's final-assembly centers in Kalamazoo, Mich., and Puurs, Belgium, and adding storage capacity at distribution sites in Pleasant Prairie, Wis., and in Karlsruhe, Germany, in addition to dozens of cargo flights and hundreds of truck trips each day. Pfizer declined to comment on United's role in the plan.

United plans to fly chartered cargo flights between Brussels International Airport and Chicago O'Hare International Airport to support distribution of the vaccine, according to a Nov. 24 letter from the Federal Aviation Administration viewed by The Wall Street Journal.

The FAA said in a statement Friday that it was supporting the "first mass air shipment of a vaccine," and that it is working with airlines to safely transport Covid-19 vaccines.

United had sought permission to carry more dry ice than is typically allowed on flights to maintain the extremely low temperatures required to prevent Pfizer's vaccine from spoiling. The FAA said it would allow United to carry 15,000 pounds of dry ice per flight -- five times more than normally permitted. Regulators restrict the amount of dry ice that can be carried on passenger jets because they typically lack equipment to monitor and mitigate any leaked carbon dioxide.

Pfizer designed suitcase-size boxes packed with dry ice to keep its vaccine doses cold, avoiding the larger, temperature-controlling containers used in transportation, giving it more flexibility to ship the vaccines faster.

Last week, Pfizer requested U.S. authorization for emergency use of the Covid-19 vaccine it developed with BioNTech SE of Germany. The FDA has scheduled a Dec. 10 meeting for a panel of outside advisers to help review the evidence behind Pfizer's request and vote whether to recommend that the vaccine be cleared for broad use in the U.S. The FDA could make that determination soon after the advisory panel's vote, setting up the potential for the start of distribution by mid-December.

Unlike traditional vaccine rollouts, Pfizer plans to bypass distribution wholesalers, including McKesson Corp., which has been tapped by the U.S. government to distribute other Covid-19 vaccines through the federal Operation Warp Speed program.

Moderna Inc. has said it expects to request FDA authorization of its Covid-19 vaccine by early December. If the FDA clears it in December, officials are expected to have enough doses of both vaccines to immunize about 20 million Americans.

The U.S. Centers for Disease Control and Prevention has been in talks with state immunization officials to identify sites in each state where vaccine doses can be stored while awaiting FDA clearance.

Other cargo and passenger airlines are also preparing for the global push to get vaccines to the public quickly. FedEx Corp. and DHL International GmBH have introduced temperature-monitoring systems to track future vaccine shipments. United Parcel Service Inc. and Deutsche Lufthansa AG are building "freezer farms" combining multiple refrigerators at their airport hubs to store vaccines in transit.

Write to Alison Sider at alison.sider@wsj.com and Peter Loftus at peter.loftus@wsj.com

(END) Dow Jones Newswires

11-27-20 1656ET