Major airlines are joining the effort to distribute the Pfizer vaccine in the battle against COVID-19.

United Airlines practice flights began Friday in an effort to be ready to move quickly once the FDA and other regulators approve the vaccine.

The flights will be allowed to carry five times the amount of dry ice normally permitted onboard to keep the vaccine at the required cold temperature.

Other cargo and passenger airlines, including American Airlines, have also begun preparing for future vaccine shipments as well.

It will be a major undertaking for all companies involved as they transport the vaccine by air and on land to distribution centers throughout the U.S. and internationally while keeping it at sub-zero temperatures.

There will be measures in place to monitor deliveries and protect against theft.