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With the new variant of concern Delta AY.1 or Delta Plus gradually istamping its footprint across the nation, a single case has even been reported in Odisha, given its 'high transmissibility' potential, is it going to trigger a third wave as severe or more severe than the second wave triggered by Delta variant in the country?
Dwelling on the possibility of third wave of the pandemic in the country, an ICMR (Indian Council of Medical Research) mathematical model analysis, however, discounts such a possibility.
The ICMR model inferred that a more severe third will be possible in the country, provided the more transmissible variant (Delta Plus) need to exceed a high threshold value (R0 >4.5) of infection to cause a third wave on its own.
Simply put, the net infection or transmission rate of the variant should be such that one infected perosn can spread the disease to 4 others.
Is Third Wave Plausible?
The ICMR study model explains that a Third wave is possible if ....
• A new variant that is more transmissible and at the same time capable of escaping prior immunity.
• Lockdowns that are highly effective in limiting transmission are subsequently released.
The ICMR model analysis infers that even in both scenarios, any third wave seems unlikely to be as severe as the second wave. However, at the same time it observed, "Rapid scale-up of vaccination efforts could play an important role in mitigating these and future waves of the disease."
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Why Third Wave Fear Looms?
Basically, the fear of third wave looms over the country, including Odisha, purely on the international experiences. Many countries (USA to UK) world over had witnessed a severe second wave after first wave. Incidentally, India too witnessed a very severe second wave recently.
Therefore, since Third waves gripped the same countries like UK and USA, the fear of third wave visiting India has been talked upon.
Will Third Wave Follow The Script?
ICMR study says unlikely. The study gives the following reasons.
• The third wave in the countries has been driven by a range of factors, not on mutant variant alone.
• It says, for example in the UK, the third wave of SARS-CoV-2 occurred during the winter months of 2020, coinciding with their annual influenza season in the northern hemisphere, but also following the relaxation of lockdown restrictions there.
• Similar factors drove a winter resurgence of COVID-19 in the USA as well.
The interpretation here is seasonal factors and full relaxation of lockdown had played a major role in triggering the third wave in the foreign countries.
But In India, the thumb rule doesn't apply....
• ICMR says, in India, seasonal drivers of transmission are likely to have a more understated role than the countries in the temperate regions.
• The evidence it has cited is the lack of any temporally coherent ‘influenza season’ across the length and breadth of the country.
Can Third Wave Be Ruled Out?
Since the epidemiological behaviour of virus suggest wave of attacks, the ICMR model identifies the 4 hypothesis that can act as a trigger factor for another wave. They are:
• If the immunity of population in the country nosedives despite no change in the virus.
• Emergence of a new virus variant that is capable of escaping pre-existing immunity
• Emergence of a more transmissible variant without loss of immunity to previously circulating strains
• Fresh opportunities for transmission afforded by the relaxation of local restrictive measures (lockdowns) in response to the second wave
The study agrees to the fact that immunity developed against Covid-19 may diminish and one can see re-infection. But in such scenario, the wave will be benign, it observed.
• Dwelling on the second possible case where a new variant capable of escaping the immunity induced by the previously circulating strains and also highly transmissible, may trigger the third wave.
• Taking such an epidemiological factor into consideration, the ICMR model then worked out the R0 value. It tried to find out what infection rate is required for the third wave to become more severe.
• The model finds that R0 value should be greater than 4.5 from the current value of 2.2 in the second wave.
Above all, the study finds that if India vaccinates around 40 per cent of the population by August, then conservative estimate shows that it will reduce the severity of the epidemic by 60 per cent.
The Bottom Line: Given such limiting factors at play here, the ICMR study says that it is 'very unlikely' that the third wave in India will grow as severe as or more severe than second wave. But the rider it adds then is if states allow the transmission line to work unhindered than that can be possible
