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 India may require the third dose of Covid vaccine by the middle of next year, said eminent scientist and biochemist Prof G. Padmanaban, as breakthrough cases even after full vaccination have been prevalent, even though mostly mild.

Prof. Padmanaban, who is Chancellor of Central University of Tamil Nadu and a Padma Bhushan recipient, said that his opinion of a third dose is based on "scientific understanding".

"In an infection by the Delta variant, which is widespread, there is a six-eight fold drop in the potential of antisera from vaccines to neutralise the variant compared to the wild type (used for vaccination- spike or whole virus).

"Nobody still has a clear answer to how long the protective antibodies will last, it has been variably estimated to be between six months and one year. If the virus has not weakened by itself, by that time, there is possibility for a re-infection," he said.

As scientists' understanding of cell-mediated protection (cellular immunity and humoral immunity) is still evolving in the case of Covid, "a third dose (sometime mid to late next year) by mix and match, also gives an opportunity to give a different vaccine against the variant," he noted.

The US Centers for Disease Control and Prevention defines a vaccine breakthrough infection as the detection of SARS-CoV-2 RNA or antigen in a respiratory specimen collected from a person more than 14 days after they have completed all recommended doses of an authorised Covid-19 vaccine.

Globally, many studies and scientists have claimed that two-doses of a Covid vaccine are sufficient for preventing infection, hospitalisation and death by SARS-CoV-2 virus.

However, the Delta Covid variant, which has now spread to more than 185 countries, as per the World Health Organisation, renewed the debate for Covid boosters. Israel, which was one of the first countries to fully inoculate (two doses) the majority of its people, suffered badly due to the Delta variant. It again became one of the first countries to roll out a third dose for its citizens.

"As far as the variants are concerned, the Delta variant is not the end of the story. The larger question is -- do we have the vaccine for every variant being created? Perhaps not. Thus, I feel that by the middle of next year, India may need the third dose of vaccine," Padmanaban, the former Director of Indian Institute of Science, said at a weekly health show by the New-Delhi-based HEAL Foundation.

While many countries, including the US, the UK, France, Germany, have rolled out of Covid booster, India is still weighing the need for it.

Scientists at the Indian Council of Medical Research (ICMR) have not approved a booster dose yet in India. For India, a booster dose is not the central theme at the moment and getting two doses remains the major priority, media reports quoted ICMR Director General Balram Bhargava as saying.

Countries which rolled out boosters, first gave the third dose to the elderly, majorly above 70, and to people with weaker immune systems. However, the Indian experts state that there is no need for booster doses in India as enough study has not been done on the subject.

Padmanabhan said: "It is essentially a case of demand and supply. We are still not able to make enough doses to vaccinate all above 18 years. We would need 1,500 mn doses (two jabs) for 75 crore population. We have only reached, perhaps, 25 per cent (two doses).

"If this population has to be vaccinated by December, we need to make at least 300 mn doses per month."

India currently has four vaccines: Covaxin, Covishield, Sputnik V and ZyCoV-D. However, Sputnik and Zydus Cadila's vaccine production needs "to be scaled up".

The other two vaccines expected in India are a mRNA vaccine by Gennova Biopharma, a subsidiary of Pune-based Emcure Pharmaceuticals, and a Recombinant RBD vaccine by Biological E, Hyderabad.

"If all these become a reality, hopefully, we can vaccinate 75 crore population before March (two doses). Giving a third dose to above 70 can only then be considered. In the meanwhile, children aged 2-18 have become another segment. Public health experts have to decide," said Padmanaban.

The 83-year-old scientist said in his opinion "the SARS-CoV-2 virus has weakened and even if there is a third wave it is likely to be mild".

But the probability of SARS-CoV-2 visiting us every year, like the flu virus, can only be a "speculation" at this stage, he said.

"This tiny virus has challenged the scientists, despite our claim of huge scientific and technological progress, a lesson in humility!" he said.