The World Health Organization-backed COVAX vaccine sharing facility has an agreement to send out "hundreds of millions" of Johnson & Johnson shots, Kate O'Brien, director of WHO's department of immunization, said on Wednesday.

COVAX, backed by WHO and the Global Alliance for Vaccines and Immunization, aims to secure 2 billion vaccine doses by the end of 2021.

In early March, it said the target was to deliver 237 million doses of AstraZeneca's shot to 142 countries by the end of May, and it also shipped its first Pfizer shots.