ROME — American pharmaceutical company Pfizer and German company BioNTech have pledged to deliver 2 billion doses of their COVID-19 vaccine to middle- and low-income countries over the next 18 months.

The companies, which together developed the first vaccine to be authorized for use in the United States and Europe, made the announcement Friday at a global health summit in Rome co-hosted by the European Union’s executive arm and Italy.

Pfizer CEO Alain Bourla says they expect to provide a billion of the doses this year and another billion in 2022.

It was unclear whether the deliveries would take place through the U.N.-backed COVAX program, which aims to ensure equitable access to COVID-19 shots for low-and middle-income countries, or if nations would get the doses at a reduced price.

The summit is drawing the Group of 20 industrial and emerging market nations, the heads of international organizations and representatives of global health bodies.

As vaccination campaigns continue to progress in the Western world, poorer countries are struggling to acquire supplies. This week, the U.N. Security Council expressed concern about the small number of doses that have reached Africa.