Swedish-British company AstraZeneca and the University of Oxford released information Monday on the efficacy their coronavirus vaccine, AZD1222. In India, a version of this vaccine (Covishield) is currently under testing:
What are the findings?
AZD1222’s efficacy (its ability to reduce the occurrence of symptomatic Covid-19 in those vaccinated) varies depending on the combination of doses administered during the ongoing trials in the UK and Brazil. According to the interim analysis, AZD1222 was found to bring down by 90% the number of symptomatic Covid-19 cases in those receiving a combination of half a dose of the vaccine followed by a full dose a month apart. But the efficacy seemed to drop to 62% when the vaccine was given as two full doses at least a month apart.
It is significant that a combination of a lower dose and a higher dose were found to actually bring about a higher efficacy. This means that more people can be effectively vaccinated using the same limited supply, which might make the candidate attractive for governments targeting a larger population.
What explains the lower efficacy with two full doses?
This is not yet clear. While experts are speculating about possible reasons, they are waiting on more data to make an informed opinion.
“I would say that it is possible that a lower dose exposure initially primes the system much better, and the second dose takes the body’s immune response to a much higher level, but this is speculative,” said Dr K Srinath Reddy, President, Public Health Foundation of India. “It is likely that, if the first dose itself is so high that it exhausts the body’s immune response, the next dose does not actually elicit the nature of heightened response required. It might be like changing the gears too fast when driving a car — you might heat up the engine, but it might not necessarily mean speed. That’s a possibility here, but it needs to be explored.
What does this mean for Covishield ?
Covishield, developed by the Serum Institute of India (SII) using the “master seed” of AZD1222, is undergoing late-stage human trials in India on 1,600 participants. The trial aims to study the safety and immunogenicity (ability to provoke an immune response) of Covishield when compared with the vaccine developed by Oxford and AstraZeneca.
According to experts, this is a bridging study that may help SII launch Covishield in India by using additional information from the global trials of AZD1222 to support its applications to the Indian drug regulator. If the study proves the two candidates are similar, the efficacy results that SII gets may also be similar.
There is a caveat: it is not clear whether the Covishield trials have been testing participants with different dosing regimens the way the AZD1222 trials are being conducted.
“If they’re using only the full dose-full dose regimen, it is likely that Covishield may come out with a similar efficacy readout of around 60%. This would still be enough for them (SII) to apply for approvals from the Indian drug regulator, because its guidelines suggest that a vaccine has to meet an efficacy of around 30-50% for a Covid-19 vaccine to receive approval,” said Massachusetts-based vaccine expert Dr Davinder Gill. “Right now, a lower efficacy of 60-70% may not be a big issue, because India doesn’t have a Covid-19 vaccine yet. But, a year from now, when multiple vaccines have been approved, then a 15-20% difference in efficacy will matter,” he said.
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How does this vaccine compare to other candidates on efficacy and cost?
Other vaccines that have announced efficacy information include those by Pfizer-BioNTech, Moderna with the US National Institute of Allergy and Infectious Diseases (NIAID) and Russia’s Gamaleya Research Institute of Epidemiology and Microbiology. None of the announcements, including AstraZeneca’s, have been published in a scientific journal and peer-reviewed, which means more information on their data is still yet to be seen.
Pfizer says its vaccine with BioNTech, which uses mRNA technology, has an efficacy rate of around 95%. However, the candidate requires nearly cryogenic levels of cold storage — making large-scale delivery a challenge in countries like India. Its pricing, yet to be announced, is estimated to be more than $19 (over Rs 1,400) a dose.
Moderna and NIAID’s vaccine, which also uses mRNA technology, has an efficacy of around 94.5%. While it requires deep freezers of around –20°C, it can also be stored in refrigerated temperatures of around 2°C to 8°C for up to a month. This vaccine is costly — around $25 to $37 a dose for different governments — making it prohibitive for countries like India, according to experts.
Russia’s Sputnik V vaccine uses a technology similar to AZD1222 and Covishield — a non-replicating viral vector. The Russian Direct Investment Fund (RDIF) said it had an efficacy of around 92%. This vaccine is stored at —18°C in its liquid form and around 2°C to 8°C in its freeze-dried form, which might make it easier to transport across large geographies. RDIF has said its cost will be “much lower” than the Pfizer and Moderna vaccines.
In India, SII CEO Adar Poonawalla has said that Covishield, which can also be stored at temperatures between 2°C and 8°C, will be priced at around $3 a dose for the government and nearly $7-8 for the “general public”. 📣 Express Explained is now on Telegram
What questions remain unanswered?
Experts say the biggest question about any Covid-19 vaccine is the uncertainty surrounding how long the immune response it generates will last.
“We still do not know the duration of protection. We have reasonable information on efficacy, but it’s not complete and not scrutinised by the regulators. We also have partial information on safety, because some of the delayed effects of the vaccine are still not known,” said Dr Srinath Reddy.
How soon can India get this vaccine? Will everyone get it?
While SII has already begun stockpiling doses of Covishield — it announced this month that it had already manufactured around 40 million doses for India — the firm has also clarified that the vaccine will be limited to priority groups like frontline workers and the elderly to start with. It would likely be available for the general population by April, according to Poonawalla.
Last week, he said the firm would apply to the Drug Controller General in India for emergency use authorisation, likely in December, if AZD1222 received such approval in the UK and Europe following positive results.
While it is aiming to ramp up monthly production from 50-60 million doses to 100 million by February, experts like Dr Reddy caution that access will also depend on aspects like whether there are enough trained personnel to administer the vaccine to a larger population.
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