SARS CoV2 Evolution: The end, or endemic?

SARS CoV-2 has not yet attained the ‘endemicity’ profile of predictable stability in form or comforting constancy in causing only mild disease

During 2020, there were claims that the Covid-19 virus would be vanquished by the vaccines when they arrive and several scientists and policymakers spoke of eliminating the virus in 2021.

Omicron is dominating the global headlines through its rapidly spreading BA.1 and BA.2 sub-lineages as well an intriguing cameo appearance from Deltacron, which combines some features of Delta. Western Europe and East Asia are experiencing a rising number of cases, but are responding differently. The UK and Europe have lifted restrictions, willing to accept a high load of infections while citing low levels of deaths as proof of protection from high vaccination rates.

In contrast, China has locked down the Jilin province and confined the residents of Shenzhen to a euphemistically phrased “pause in life” state of immobility. South Korea never locked down but is testing extensively and strictly as well as implementing public health protocols of masking and physical distancing. Even as infections crossed a record 600,000 per day, deaths have remained very low due to high rates of vaccination.

India began opening up confidently, after a brief Omicron wave that caused much less damage than Delta, but the health secretary has recently warned the states that continued caution is warranted. Daily case and death counts continue to fall, but there is concern that the global contagion could still affect us. As the media seeks explanations for India’s contrasting experience, speculation is now focused on the virus becoming endemic.

Over the course of the pandemic, pendulum has swung from claiming that India attained invincible ‘herd immunity’ (after the first wave) to ‘impenetrable hybrid immunity’ (after the Delta wave and vaccines) to ‘we can live with an endemic virus’ (after the Omicron wave). How valid is the assumption that the virus has attained endemicity?

During 2020, there were claims that the Covid-19 virus would be vanquished by the vaccines when they arrive and several scientists and policymakers spoke of eliminating the virus in 2021. When the Delta wave hit India initially during February-June 2021, the continuing threat of the virus came as a shock to many who had sworn that India had acquired herd immunity by January 2021.

As antibody surveys revealed high rates of viral exposure in the population after Delta and vaccines began to be rolled out at scale, the idea of hybrid immunity gained ground before Omicron arrived. The immunity levels in the population did keep that wave shorter, with much less damage compared to Delta. However, it was a reminder that the virus can still strike at people whose immunity wanes over time. That message is getting amplified by the ongoing experience of many countries.

The virus will stay, but has it already become ‘endemic’? Remember, the media were excited in August 2021, when the WHO’s Chief Scientist opined that “India may be entering the endemic stage of Covid”. It was interpreted by many that the endemic state had arrived or was imminent. Then came Omicron, to rudely remind us that it had not. Are we now at the stage of endemicity?

The dictionary defines an endemic infectious agent as ‘persisting in a population or region, generally having settled to a relatively constant rate of occurrence’. This requires the virus to be stable and predictable in its behaviour. It may cause periodic spikes or be infectious throughout the year but there would be no unanticipated upsurge.

Endemic diseases can be regionally distributed and even cause serious diseases and deaths (like TB and malaria in Africa and Asia or the chagas disease in Latin America).

The coronavirus has not attained that profile of predictable stability in its form or comforting constancy in causing only mild disease. On March 16 this year, Israel’s health ministry announced the emergence of a variant which combines features of BA.1 and BA.2. The virus is still actively mutating and spreading, with high rates of severe disease in persons with low levels of immunity. The SARS-CoV-2 virus has not yet joined the club of common cold coronaviruses. It may, however, be applying for the membership of that club.

Viral studies on Omicron have shown that it heavily occupies the nose and throat but is mostly unable to invade the lungs. Clinical descriptions of the Omicron infection too have reported far higher frequency of a running nose (80% in some case series) and far less of breathlessness and pneumonia, compared to earlier forms. This suggests the virus is evolving to become a stable but much less menacing co-habitant of human communities.

Such an evolution of this respiratory virus to a relatively stable form of high infectivity and low to moderate virulence, would be keeping in with the survival logic of evolutionary biology. The virus needs humans who are numerous, reproduce to higher population levels, and are highly mobile to keep itself in wide circulation. Of all the mutations it accidentally produces, those which serve the goal of tagging humans are retained.

Deer and minks may get infected too but they will not become the luxury carrier that humans provide to cross continents. Humans provide the virus the best guarantee of its species survival. However, there is a danger that the virus could experience an ‘antigenic shift’ in an animal which also harbours another virus which permits a swap of some genetic material.

That can potentially create a virulent variant which may cause some harm if there is animal to human transmission before it yields place to a less virulent one.

Such an antigenic shift can also occur in an immunocompromised human.

It appears that the virus is still figuring out its future on this evolutionary track, just as we are figuring out how to block its travel from person to person and country to country. We have not yet landed on the runway of endemicity. We are still circling that airport and need to keep our seatbelts on.

The author is President, Public Health Foundation of India (PHFI) and Views are personal

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First published on: 24-03-2022 at 04:20 IST