A number of developing nations have refused tens of millions of doses of AstraZeneca’s COVID-19 vaccines, according to a report from Reuters.

The countries had received doses of the AstraZeneca vaccine from the COVAX initiative, a global project that focuses on ensuring equitable access to COVID-19 vaccines.

COVAX has distributed 1.4 billion shots to 144 nations to date.

Some countries that COVAX serves indicated a preference for vaccines with a longer shelf life than AstraZeneca’s COVID-19 vaccine.

Last week, COVAX and the African Union also declined to order vaccine doses from Moderna, according to Reuters.

AstraZeneca’s COVID-19 Vaxzevria has a shelf life of six months, but doses are sometimes delivered weeks before the expiration date, Reuters reported.

In related news, Japan recently canceled a purchase of 40 million doses of the AstraZeneca vaccine, according to The Japan Times.

The country has expressed a preference for mRNA-based vaccines from Pfizer and Moderna.

AstraZeneca was initially a central provider of COVID-19 vaccines.