All of the doses will be used this year, promises current AU head South African President Cyril Ramaphosa.
This is on top of 600 million doses already secured but is still not enough to vaccinate the whole region.
There are fears that poorer countries globally will wait far longer than richer nations to be inoculated.
Although infection numbers and death rates are comparatively lower across most of Africa, cases are spiking again in some areas.
A new variant of Covid-19 in South Africa is causing particular alarm and makes up most of the new cases.
"As a result of our own efforts we have so far secured a commitment of a provisional amount of 270 million vaccines from three major suppliers: Pfizer, AstraZeneca (through Serum Institute of India) and Johnson & Johnson," President Ramaphosa said on Wednesday.
At least 50 million of the doses will be available "for the crucial period of April to June 2021," he said.