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, January 21
Seasonal coronaviruses causing common cold provides a potential roadmap about how SARS-CoV-2 might evolve, according to Dr Satish Ranjan, Germany-based molecular immunologist.
These viruses trigger repeat infections but it was not known until evolutionary biologist Jesse Bloom carried out a landmark study to determine whether these were attributable to fading immunity in humans or mutations of the virus that evaded immunity, Ranjan told BusinessLine.
Four common cold viruses
“Out of the four coronaviruses causing common cold, one, namely 229E, was found to repeatedly infect humans. Bloom studied the effect of antibodies derived from old blood samples of the infected people against different versions of the virus going back to the 1980s,” Ranjan explained.
Results from Bloom’s study showed that blood samples from the 1980s contained high levels of infection-blocking antibodies against the 1984 version of 229E. But they had less neutralising capacity against the 1990s versions and even lesser against later versions of the 2000s and 2010s.
Immune against recent infections
The 1990s blood samples too had generated similar results, suggesting that humans had immunity only against the most recent viral infections but not to those of the future versions. This significant finding proved scientifically that this coronavirus was evolving to evade immunity.
This seems to hold true in the case of the current SARS-CoV-2 wherein the original strain from 2019 had evolved into various strains like Delta with immune escape abilities and caused severe disease during the second wave. It escaped even immunity gained after natural infection during the first wave.
Holds true with SARS-CoV-2
The Omicron strain has also been found to escape immunity gained during previous infections suggesting that it too has evolved with immune escape abilities. “The manner of the spread and the disease severity suggests that humans have no immunity for evolving new strains,” Ranjan said.
Further, immunity gained after natural infection also declines after 8-10 months as revealed by scientific studies and real-world data of re-infections available ever since. The third wave in India is largely driven by Delta due to fading natural immunity gained during the second wave.
No absolute blanket immunity
“Since Omicron variant evades natural immunity gained during the previous wave, it is certain that there is no absolute blanket immunity against future strains,” Ranjan pointed out.
It is likely that any existing strain will not provide blanket immunity against future variants and thus ring mass herd immunity or work as a natural vaccine and bring the pandemic to an end. “It could become endemic and our immune system may evolve to fight new variants as is the case with the common cold,” he said.
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