"The agreement is legally binding and served as a basis for the first-round allocation document, which has been communicated to all participating economies," a Gavi spokeswoman said in an email.
The pact specified Gavi would receive from SII 1.1 billion doses of either the AstraZeneca
vaccine or that of Novavax , with 200 million committed, and the rest on option.
SII partner AstraZeneca
has already issued it a legal notice over delays to other shipments, even as many Indian states have complained of a shortage facing priority recipients.
Gavi said its pact with SII took effect when the World Health Organization approved the AstraZeneca
shot on Feb. 15, after a source said SII had originally been supposed to send doses to COVAX only from May.
"SII has pledged that, alongside supplying India, it will prioritise the COVAX multilateral solution for equitable distribution," Gavi added.
COVAX had expected
a total of more than 100 million doses from SII between February and May, excluding supplies for India, but has so far received
only about 18.2 million.
Serum has sent another 10 million doses to the Indian government through COVAX, Gavi said.
Gavi did not respond on Friday to questions about what now lies ahead. SII also did not immediately respond to a request for comment.
From an initial August target of vaccine coverage for 300 million of its highest-risk people, or just over a fifth of its population of 1.35 billion, India has upped the figure by about 100 million, adding pressure on SII to crank up supplies.
India could resume vaccine exports by June, the firm's chief executive, Adar Poonawalla, told media this week.
The firm has also sought $403 million from New Delhi as a grant to boost monthly output to more than 100 million doses by end-May, from 65 million to 70 million now.
On Thursday, the foreign ministry said domestic demand would determine the extent of India's exports. It has already shipped 64.5 million doses and given out 92 million at home.
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