As India begins one of the world’s largest COVID vaccination drives, Dr Samiran Panda, Head of Epidemiology & Communicable Diseases Division with the Indian Council of Medical Research – National AIDS Research Institute underlines the various stages of vaccine development adding that a March 2019 amendment in rules for new drugs and clinical trials in India allows for accelerated drug approval.
How do you see the role of a vaccine when the number of cases are fast coming down in India?
The COVID epidemic curve is on a decline but India is a huge country and there are some States where we are seeing second and third waves of the infection. Also there are places where the case fatality rate is still above the national average. Moreover, new mutants are making their appearances and we are yet to understand them fully.
Look globally. Never before had the scientists come up with a vaccine in such a short time. It was January 12, 2020, when scientists decoded the genomic make-up of the virus and so many vaccines were ready to enter the clinical trials in less than 10 months. We are, after all, dealing with a virus which is easily transmissible. And it leaves a devastating effect on people, especially those who are elderly and those who are suffering from chronic illness.
Bharat Biotech’s Covaxin has been approved before it completed its phase-III trials. How do you look at the decision?
We are struck by a pandemic. In such a crisis, scientists and regulatory authorities have to be innovative and find faster ways of assessment of a vaccine but certainly not at the cost of safety.
Phase-I trials primarily test a vaccine for its safety. Phase-II trials test it for its immunogenicity while additional safety data is also obtained. In phase III, we give vaccines to one group and placebo to another and examine if the number of infections in the group to which placebo was given are significantly higher than the group vaccinated. This number should be significantly higher for us to know that the vaccine is protecting against the possibility of acquisition of the virus.
The regulatory authority must have considered all these points before it approved Covaxin To answer some critical questions, such as if we can wait for the phase-III trial to complete, the regulators have to look at various aspects of the pandemic — how it is impacting on lives, and how promising a particular vaccine candidate seems to be, based on the data available at hand.
Please explain the various stages of vaccine development in the context of Covaxin?
A vaccine is tested first in small animals such as mice, hamsters, and rabbits with a focus on efficacy and particularly potential toxicity. Following encouraging results, vaccines are then tested in larger animals such as rhesus monkeys as certain human diseases are mimicked in them. The vaccine, under scrutiny, is given to one group of animals which is then exposed to the virus, and a second group is exposed to the virus without being administered the vaccine. In the case of Covaxin, we found that the vaccinated animals were able to clear off the infection from their respiratory tract much faster. Histopathology revealed that all their tissues were normal, whereas the animals, who were not vaccinated, the tissue damage following challenge with the virus (SARS-CoV-2) was extensive.
After this, when the ICMR-Bharat Biotech vaccine was moved to phase-I of human trials, to check for its safety in humans. The results, I must tell you, were highly impressive. You know, a vaccine is scrutinized on three critical parameters first is safety, second if it gives rise to adequate immune response (its immunogenicity), and third, how long the immune system memorises the infection (the durability of the vaccine effect).
Is there a provision to approve a vaccine before it completes its phase-III trial?
On March, 19, 2019 (much before the COVID-19 hit the world), a provision was added to the new drugs and clinical trial rules in India to drug approval process. Under this provision, in situations where there is a threat to life or danger of disability due to a disease and where we do not have a better treatment alternative, phase-II clinical trial results, if remarkable, could help in facilitating an accelerated approval of a drug, which is yet undergoing a trial and yet unregistered.
It is being said that Covaxin could be more effective to fight the new mutant coronavirus variant. How?
Post-vaccination immune status of an individual, which would counter the effects of a new mutant of the same virus on its host, is dependent on multiple factors. Although, some of them are yet incompletely understood, the inactivated whole virion used in the development of Covaxin is expected to achieve a wider antigenic presentation to our immune system resulting in a versatile spectrum of immunity.
Worth noting in this regard is that whole inactivated virus induced immune response, in some experiments, have fared better compared to the subunit vaccines in case of influenza. Whether a similar phenomenon would hold true at population level for COVID-19, needs to be examined over the coming years. In the meantime, well-designed laboratory experiments could throw some light in this regard.
It will not be inappropriate to mention here that some of the viruses, such as influenza, have evolved mechanisms to evade recognition by immune memory. Slight change in viral structural proteins, known as drifts, is one of these mechanisms, which cause local epidemics by avoiding recognition of the progeny virus by the poorly efficient immune system. On the other hand, when the influenza virus replaces one of its genes with a new one — a major change indeed — that is called shift and such radically different influenza viruses, sweeping through the world, are capable of causing pandemics.
