Serum Institute of India, which has partnered with AstraZeneca to manufacture its Covid-19 vaccine, will continue to test a two full dose regimen of the shot despite it showing a lower success rate than a half and full-dose regimen in pivotal trials, a top executive told Reuters.
The British drugmaker has said its Covid-19 vaccine could be up to 90% effective if administered as a half dose followed by a full dose, but some scientists have questioned the robustness of that result because only a few thousand people were given that regimen in late-stage UK trials.
The global trials showed the efficacy rate of the shot was 62% if the full dose was given twice, as it was for most study participants in trials in Britain and Brazil. AstraZeneca has said it is likely to run an additional global trial to evaluate the lower dose regimen.
SII which is currently running trials in India testing the safety of AstraZeneca's vaccine, as well as the immune response it triggers, has no plans currently to alter them to include the half dose-full dose regimen, according to Dr Suresh Jadhav, an executive director at SII.
"Anything which is beyond 50% is always going to be a plus, plus," Jadhav said in an interview on Monday, referring to efficacy rates. He added that changing the dose regimen now would delay the trials.
A combination of two different measures could also complicate rapid distribution efforts, according to Jadhav, who has worked on vaccines for over four decades.
"When it is one common dose it becomes very easy. Whether it is the first dose, or second it is the same vaccine, same dose," he said.
Over the weekend, SII said that it planned to apply for an emergency use licence for the vaccine in India in the next two weeks.
The 62% efficacy rate on AstraZeneca's broader two full dose trial is above the 50% that US regulators say is the minimum required to consider a drug for emergency authorisation.
SII, based in the western city of Pune, is the world's top manufacturer of vaccines by volume. Beyond AstraZeneca, it has also partnered with other companies to potentially manufacture their shots, including US biotech firm Codagenix; its rival Novavax and Austria's Themis.
But in the global race to develop vaccines to beat the pandemic, AstraZeneca's vaccine is one of the frontrunners despite having lower efficacy rates than some rivals.
US drugmakers Pfizer and Moderna have said their coronavirus vaccines have an efficacy rate of 95% and 94.5% respectively but AstraZeneca's drug is cheaper and easier to transport because it can be stored for long periods at normal fridge temperatures.
Those advantages are particularly important for many developing countries and, therefore, for SII. As part of a deal outlined in June, AstraZeneca has licensed SII to supply one billion doses of its vaccine to dozens of low and middle-income nations.
Most of the nations that are part of the COVAX initiative, which has been set up to provide Covid-19 vaccines to poorer countries, have indicated they would accept and use a proven vaccine, if it showed more than 50% efficacy, according to Jadhav.
Adar Poonawalla, the CEO of SII, said affordability, scalability and ease of storage and transportation were key factors for India and other emerging economies as they look to decide on large scale purchases of vaccines.
"A vaccine that cannot penetrate and be given in a large population to provide high vaccine coverage you may as well not give it at all," Poonawalla told Reuters.
"If it's not affordable and logistically transferable, even if it is 110% effective what is the sense?"