India is launching one of the world's largest vaccination campaigns. But it's unclear if one of the vaccines works.

India is set to launch on Saturday one of the world's largest vaccination campaigns with the aim of immunizing 300 million people by this summer.

The mammoth undertaking is a leap forward in the fight against the coronavirus in India, second only to the United States in its total number of cases.

The effort is being buoyed by two locally-made vaccines and India's prior experience with large-scale immunization campaigns. But what might have been a triumph for the country's vaccine industry has been dogged by controversy.

The Indian government granted emergency approval to two vaccines - a locally manufactured version of the Oxford-AstraZeneca vaccine and a vaccine called Covaxin developed by Bharat Biotech, an Indian pharmaceutical company.

Only the Oxford-AstraZeneca vaccine has completed a Phase 3 clinical trial for safety and efficacy. Bharat Biotech has finished earlier-stage trials on its vaccine but has so far provided no data on whether it works. Yet both vaccines will be administered starting Saturday, and people being immunized will not be able to choose which they receive.

Complicating matters further, Indian regulators have said that the Bharat Biotech vaccine will be used in "clinical trial mode," a phrase that left experts baffled. One of India's foremost vaccine experts, Gagandeep Kang, told an interviewer that she had "no clue" what it meant.

Unlike the United States and the United Kingdom, India is starting its vaccination campaign at a moment when the virus is in retreat. New cases have dropped drastically since peaking in September: India is recording about 14,000 cases a day and fewer than 200 deaths.

The massive vaccine push is expected to kick off at 3,000 sites across the country on Saturday, a number that authorities say will grow in the coming weeks.

To start, the Indian government has purchased 11 million doses of the AstraZeneca vaccine, manufactured by Serum Institute of India, and 5.5 million doses of the Bharat Biotech vaccine. Both vaccines were sold at $2.75 a dose (the Pfizer vaccine, by comparison, costs $19.50). If targets are met, 300,000 people could receive doses on Saturday.

The first to receive vaccines will be approximately 30 million health-care workers, soldiers, paramilitary personnel and municipal employees dealing with sanitation. They'll receive it free of cost. Then the immunization drive will target 270 million people over the age of 50 as well as those below 50 who have co-morbidities.

The rollout of the vaccine program matters not just for India, but for the entire developing world. India is a vaccine powerhouse with a proven track record of low-cost manufacturing. Serum Institute of India is the world's largest vaccine maker by volume.

Serum Institute will be a major supplier to COVAX, a global initiative backed by the World Health Organization to distribute vaccines equitably to poorer countries. Several countries - including Brazil, Bangladesh and Nepal - are looking to purchase vaccines directly from Indian companies.

Adar Poonawalla, the chief executive officer of Serum Institute, said that the company would start delivering doses to COVAX by the end of this month. The company has also forged deals to supply the AstraZeneca vaccine to Saudi Arabia, Bangladesh, Myanmar and Morocco, he said.

In India, health officials have been preparing for weeks - registering recipients, training vaccinators and conducting dry runs. Neither the AstraZeneca vaccine nor the Bharat Biotech vaccine requires ultracold storage, a crucial plus in a country such as India.

Rajesh Bhaskar, the official in charge of covid-19 management in the state of Punjab, said he expected to be able to vaccinate 30,000 people on Saturday and to complete the immunization of the state's health-care workers within 10 days.

"There is a sense of relief, big relief," he said. "We hope this will suppress the pandemic and eventually we will get rid of it."

The distribution effort has already spread across the country. In Chandrapur, a predominantly rural district in central India, an initial shipment of 20,000 doses of the AstraZeneca vaccine arrived by road in a government van earlier this week.

They were stored in an ice-lined refrigerator guarded by a private security firm specially hired for the occasion, said Rajukumar Gahlot, the district's health officer. Nearly 100 health-care personnel in the district have contracted covid-19, he said. Six of them died.

The AstraZeneca vaccine will represent the large majority of vaccines administered on Saturday, but Covaxin is also a key part of the launch, particularly in cities. There remains "a lot of conjecture" around how regulators reached the decision to grant emergency approval to the Bharat Biotech vaccine in the absence of efficacy data, said Anant Bhan, a public health and bioethics expert.

Bhan said that by granting approval to Bharat Biotech's vaccine in "clinical trial mode," regulators raised many unanswered questions. Critics of the government went further. "Indians are not guinea pigs," Manish Tewari, a spokesman for the opposition party, told Asian News International.

Bharat Biotech declined to respond to questions about concerns over the efficacy of its vaccine, but it has pointed to the results of early-stage studies showing an immune response as an indicator of future results.

Bharat Biotech's vaccine is "incredibly safe but I don't know if the d--- thing works," said one expert on India's vaccine industry who spoke on the condition of anonymity to comment frankly. Both vaccines are "less than ideal," the expert added, noting that the data on the efficacy of the AstraZeneca vaccine showed huge variations, partly as the result of a dosing mistake.

Some experts worry that the lack of transparency in the process of approving vaccines for emergency use could undermine confidence in them more broadly. That would represent a break from the past in India, a place where vaccine skepticism is low and immunization is seen as an essential tool in reducing mortality.