The Serum Institute of India is legally compelled to ship coronavirus vaccine to global vaccine sharing facility Covax, its co-lead Gavi has told Reuters, a provision that could complicate the firm’s efforts to boost domestic supplies.

India, where infections have surged to 13.06 million, suspended all major exports of vaccines last month to fill demand at home, forcing the world’s biggest vaccine maker to divert nearly all its production to the domestic market.

“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 by email.

The pact specified Gavi would receive from the Serum Institute 1.1 billion doses of either the AstraZeneca vaccine or that of Novavax, with 200 million committed, and the rest on option.

Serum Institute partner AstraZeneca has already issued it a legal notice over delays to other shipments, while many Indian states have complained of a shortage facing priority recipients.

Gavi said its pact with Serum took effect when the World Health Organisation approved the AstraZeneca shot on February 15, after a source said Serum had originally been supposed to send doses to Covax only from May.

“Serum has pledged that, alongside supplying India, it will prioritise the Covax multilateral solution for equitable distribution,” Gavi added.

Covax had expected more than 100 million doses from Serum between February and May, excluding supplies for India, but has so far received only about 18.2 million.

Gavi did not respond on Friday to questions about what now lies ahead. Serum also did not respond to a request for comment.

The firm has 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. Reuters

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.