The European Union will return to Africa millions of doses of Johnson & Johnson’s COVID-19 vaccine that it received from a plant in South Africa, following criticism by health activists that the bloc was taking away shots from a continent that has the lowest immunization rate in the world.

Strive Masiyiwa, who heads the African Union’s Vaccine Acquisition Task Team, said the decision to return the shots produced at Aspen Pharmacare Holdings Ltd. was made at a meeting between European Commission President Ursula von der Leyen and South African President Cyril Ramaphosa last week.

As part of the deal, the EU will also not take doses from the Aspen plant it was expecting in September, Mr. Masiyiwa said.