In total, 49 million doses had been distributed through Covax, of which 29 million were from Serum.
As coronavirus cases surged this month in India, the country that houses the world's largest vaccine manufacturer, the government began to pause vaccine exports.
Shipments ground to a halt by mid-April. Now, with domestic need for vaccine in India overwhelming capacity and program extending to adults over 18, it is not clear when India will begin exporting doses again.
The suspension of exports in April has contributed to a 90 million-dose shortfall for Covax, an international vaccine distribution effort, one of the group's key backers said Friday. That number will only grow in May if restrictions are not lifted.
The limited supply would be a particularly big blow for low-income nations, many of which not only sought India-produced AstraZeneca through Covax but also pursued bilateral deals with Serum Institute of India, the Pune-based vaccine giant.
Arindam Bagchi, a spokesman for India's Foreign Ministry, said Friday there was "no update" on when vaccine exports would resume.
Andrea Taylor, a researcher at Duke University's Global Health Innovation Center who leads a team tracking vaccine deals and distribution, said continuing delays in Indian exports would be "devastating" for the poorer nations, adding that Covax would probably meet only a fraction of its distribution goals for May.
"There is no contingency plan or alternate supplier for the next few months," Taylor said.
The Indian government has faced criticism for exporting millions of doses abroad before it secured enough doses for its population of 1.36 billion. Despite new case numbers that set global records and a death toll of over 200,000, less than 1 in 10 Indians have received a dose.
Even with export controls, vaccination sites in India have complained of severe problems with supply. On Thursday, Mumbai announced it would close vaccination sites in the city center until Sunday after running out of doses.
Outside India, the profound impact of the export ban suggests other manufacturing options are needed, said Thomas Bollyky, a senior fellow at the Council of Foreign Relations.
"The Serum Institute of India is a terrific contract manufacturer of vaccines," he said. "It is not sufficient to meet global needs."
In a statement, Gavi, a vaccine alliance that backs Covax, said further delays in May would be a "significant short-term challenge" for Covax.
In total, 49 million doses had been distributed through Covax, of which 29 million were from Serum, the statement said.
Officials from the African Union, which also arranged supplies from Serum, have expressed alarm, with top health official John Nkengasong saying this month that the export controls could be "catastrophic" for the continent.
Nkengasong, who heads the Africa Centers for Disease Control and Prevention, said this week that what was happening in India could eventually happen in Africa. "We are living in a world that is extremely uncertain now," he told reporters in Nairobi on Thursday.
According to data collected by the Indian government, exports of vaccine have slowed to a stop. India exported over 28 million doses in March, up from 17 million in February, with most doses coming from Serum.
That number declined steeply in April to less than 1.9 million. No vaccine has been exported since April 16, according to the Indian data.
India initially portrayed the export restrictions as a temporary measure. V.K. Paul, a top health official and co-chair of India's vaccine distribution group, said in an interview in early April that the restrictions were not a "scaling down" but a "slowing down" that would be resolved within weeks.
But with new cases in India still soaring - reaching another global record of 386,452 on Friday, with the total death toll over 200,000 - it was not clear when exports would resume.
In a bid to beat back infection rates, anyone over 18 is now eligible for vaccinations across India starting Saturday. Several Indian states have said they do not have enough supplies for the large expansion of eligibility.
Serum has said it is able to produce between 60 million and 70 million doses per month. Bharat Biotech, another Indian company that has developed a vaccine called Covaxin, is producing 10 million per month.
Adar Poonawalla, Serum's chief executive, has blamed the slow pace of vaccine production in India on U.S. export controls on raw materials, calling on President Biden to "truly unite in beating this virus" in a tweet this month.
International organizations, including Gavi and others, have also called on countries to lift restrictions on exports and release excess doses.
The United States has pledged to share its supplies of AstraZeneca, not yet approved domestically, with foreign nations. Twenty million doses are expected to go to India. The Indian government has also reached an agreement to obtain 5 million doses of Sputnik V, a Russian-backed vaccine.
Such deals will be too little, too late to stop the immediate spread of the virus. It will take weeks, if not longer, to obtain and distribute the doses. AstraZeneca, like Sputnik and Covaxin, does not confer immunity immediately and requires two doses.
"There's no way to vaccinate your way out of this surge," Bollyky said. In the short term, he added, treatment and social distancing policies may be more important.
There are concerns that other countries may be on the same path as India. Nepal, India's smaller neighbor facing its own surge, received only half of its order from Serum before India's export restriction. Less than one-tenth of its population has received a dose, and it is now seeking more supplies from Russia and China.
"For the next India, we need to be ahead of it, not behind it," Bollyky said.
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The Washington Post's Niha Masih in New Delhi contributed to this report.