“I am predicting that, as of now, a Third Wave caused by the highly transmissible Delta variant is most unlikely,” says leading virologist Dr T. Jacob John, former head of ICMR’s Centre for Advanced Research in Virology.

John’s firm belief that a Third Wave caused by the Delta variant is unlikely to happen is backed by a CSIR study of its employees which is about to be released.

In Delhi, the study found, 86 per cent of its unvaccinated employees and their families who were tested had Covid-19 antibodies. Similarly, Lucknow had high numbers and also Ghaziabad, on Delhi’s outskirts. Says Dr Anurag Agrawal, director, Institute of Genomics and Integrative Biology, who headed the survey: “It wasn’t unique to Delhi. There were many other places with high numbers.” In Delhi, 850 unvaccinated CSIR employees took part in the survey.

Most virologists say that 86 per cent positivity should be enough to create “herd immunity” even for a highly infectious virus like the Delta variant. But there is still the worry of variants that are more dangerous than the Delta emerging over time and experts say the war against Covid-19 is far from won.

Virologist Shahid Jameel explains why the earlier herd immunity calculations were thrown out of the window because of the fast-spreading Delta variant. “The better the transmission of any pathogen, the higher is the threshold of herd immunity. The simple fact is that the faster something transmits the more immunity in a population will be required to prevent its spread,” he says. Dr Jameel is director, Trivedi School of Biosciences at Ashoka University.

Calculations out of gear

When the Covid-19 pandemic erupted in 2020, most virologists and epidemiologists predicted that herd immunity would be attained when around 65 per cent to 70 per cent of the population had Covid-19 antibodies. But such calculations were thrown out of gear by the devastating Delta variant.

ICMR’s fourth serosurvey conducted between May and early July, showed that 67 per cent of Indians were seropositive or had Covid-19 antibodies. But there were sharp regional variations with 79 per cent of people in Bihar having Covid-19 antibodies and only 44 per cent in Kerala.

Since then, there have been further cases and this is certain to have pushed up the percentage of people with Covid-19 antibodies considerably. Hence another serosurvey is being done to gather the latest numbers.

Demise of Delta

Says John: “Now the question is supposing that serosurvey comes out to be 75 per cent? Will that preclude a third wave?” He continues: “It will preclude a third wave by the Delta variant. That’s because the Delta variant has died or dried out. Because the numbers are not sufficient.”

On a similar note, World Health Organization’s chief scientist Soumya Swaminathan also in a TV interview said: “India could have reached some sort of endemicity.” She added: “It is feasible we may continue like this with a few local ups and downs.”

Still, there remains the worry that more dangerous variants might emerge over the coming months and years. One possibility is the Delta variant antibodies could be ineffective against an even faster-spreading and nasty variant that challenges the effectiveness of existing vaccines.

“The virus could mutate and become more lethal,” says Dr Partha Majumder, National Science Chair and distinguished professor, National Institute of Biomedical Genomics.

Adds Dr Sandeep Juneja, dean, TIFR School of Technology and Computer Science: “Nobody envisaged the (Delta) variant that was so much more infectious. That was very unexpected. For a couple of months, we were struggling to understand what was going on.” TIFR collaborated with the Brihanmumbai Municipal Corporation (BMC) to conduct serosurveys in three city wards last year. The Korea Disease Control and Prevention Agency said Tuesday it reckoned that the Delta transmission is 1.6 times more than that of the Alpha variant and about twice as much as the original version of the virus.

Second wave

What’s called the Covid-19 ‘second wave’ began in late March and peaked on May 8 when a staggering 403,405 cases were reported. The number of daily cases fell below 1 lakh on June 7.

Different government agencies have, however, forecast that a third wave could be round the corner. A Home Ministry panel warned on Monday that a Covid-19 pandemic could peak in October and might impact children more than in previous waves. Children are considered a “vulnerable population” as vaccinations for kids has not yet begun. The ministry recommended that paediatric wards get ready for such a contingency.

More cautiously, Samiran Panda, chief of Epidemiology and Communicable Diseases, Indian Council of Medical Research last month told The Hindu that a third wave, “is a distinct possibility although not inevitable as it is dependent on the scale and quality of appropriate public health measures.” He predicted this could possibly begin anywhere between August and October.

No permanent herd immunity

The CSIR study also points out that, “despite high seropositivity, Delhi was amongst the most affected cities during the second wave.” Adds Agrawal: “To create an outbreak in a city with such high antibodies you need something that will break through immunity.” However, he warns: “As we know by now there is nothing called permanent herd immunity. Our paper speaks of reinfections.” The study showed that 27 per cent of the cases were reinfections.

At the other end of the spectrum, the CSIR survey reckons that seropositivity is still low in Kerala because the state was able to control infections there.

Jameel points out crucially that a serosurvey only measures the presence of antibodies and that can be different from having immunity. “Just having antibodies doesn’t mean that you are protected. It depends on the quality of the antibody. It depends on whether you have good neutralising antibodies and good titres,” he said. “None of that information comes from a serosurvey. A serosurvey only tells you that 67 per cent of India on average has been exposed to the virus. It doesn’t mean 67 per cent is protected from the virus.”

John, however, is confident that the Delta variant has done its worst in India. “I am predicting that as of now the third wave by the Delta variant is most unlikely.” He said there will be no further wave “unless a new variant appears on the scene.”

Pace of vaccination

In addition to the people infected by the Delta variant, in the last few months, the pace of vaccinations has also been picking up. John is highly critical of the vaccine programme, pointing out that only 13 per cent of the total population has received two doses. “Seven months after the approval of the vaccine, this is most disappointing,” he says.

Nobody believes Covid-19 is about to do a disappearing act. One expert predicts: “It will slowly turn into influenza. It is here to stay and not about to vanish.”

There could also be a dire scenario that could put us back at square one and undercut all the country’s Covid-control efforts. Says Juneja: “There is also a bad scenario: a variant that doesn’t respect any immunity we currently have.”