The world's biggest vaccine maker resumed exports of COVID-19 doses this month for the first time since April. It has sent about 4 million to countries such as neighbouring Bangladesh and Iran, but none to COVAX.
Delayed supplies to COVAX could disrupt inoculation drives in many African nations that rely on it for vaccines.
One of the sources said it was "frustrating" that India had yet to confirm any supply to COVAX, despite a promise by the health minister last month to meet the commitment to COVAX and others during the quarter to December.