One of its production partners, the Serum Institute of India, has been granted WHO approval for a nine-month shelf life, after it was initially authorised only for six. But other batches produced by AstraZeneca in the rest of the world have only six.
"We are currently in discussions with the World Health Organisation ... but this is a complex task which requires data to be collected from across our global manufacturing network," a spokesperson for AstraZeneca said.
A WHO spokesperson did not comment on the talks.
On average, African countries have used two-thirds of received doses, but that drops to 11% in Burundi and 15% in Congo, with other large countries, including Madagascar, Zambia, Somalia and Uganda, having used only about one-third, Gavi said, citing figures from late January.