The White House's commitment to ship millions of doses of COVID-19 vaccines abroad has generated diplomatic and logistical challenges for administration officials to untangle, according to NBC News.

Since US President Joe Biden announced this month 80 million shots would be shipped abroad by the end of June, the White House has yet to send out any of the doses because of a variety of hurdles, from logistical to regulatory.

White House COVID-19 coordinator Andy Slavitt said Wednesday the US is trying to move to a "tighter distribution system" so the federal government can keep better track of doses and export any additional ones.

There is also the challenge of transporting tens of millions of doses around the world, ensuring there are enough planes and making sure the doses are properly stored and the countries receiving them have the infrastructure to refrigerate and distribute them, an administration official said.

Another potential big problem is getting Food and Drug Administration authorization for the AstraZeneca vaccine.

The FDA review process has been delayed by issues with AstraZeneca's study data, and it is unclear when — or even whether — AstraZeneca's vaccine will get the green light.

The White House has said it is working with the World Health Organization and COVAX, which is working to get vaccines to lower- and middle-income countries, to make sure the doses are distributed equitably.

An administration official acknowledged the challenges of the rollout, saying the commitment is likely to be just the start.

That's because the 80 million doses would be a drop in the bucket of what international organizations say is needed. COVAX has set a goal of distributing 1.8 billion shots to lower- and middle-income countries this year.