Omicron likely to be last COVID-19 variant, says new study

It is unlikely that India will witness another major wave caused by a newer SARS-CoV-2 variant after Omicron and it is likely that Omicron will be the sole survivor of the endemic SARS-CoV-2 infection and consequent disease, states a paper co-authored by Dr T. Jacob John, virologist and former professor at the Vellore-based Christian Medical College.

According to a paper published in the journal Current Science of the Indian Academy of Sciences, Dr John, Dr Mandalam S. Seshadri and Dr Dhanya Dharmapalan have argued that Omicron has resulted
in establishing very high population immunity or herd immunity due to its universally high prevalence and as a result seemed to have brought the pandemic to an end in India.

They have found out that it was evident that the emergence of the Omicron variant was an unusual development, not fitting in the evolutionary pathway of the previous variants of concerns (VOCs), which originated from the parent Wuhan-D614G.

The authors believe that “it is most unlikely that we will witness another major wave caused by a newer SARS-CoV-2 variant after Omicron. However, Omicron is a family of sub-variants, and some have greater transmission efficiency than others. Whether one or more of them will predominate is unpredictable as of now”.

Subvariants BA.2, BA.4 and BA.5 or some recombinants may dominate the future and currently Omicron subvariant XBB.1.16 is the predominant one in circulation in India. It is a recombinant of two Omicron variants, namely, BA.2.10.1 and BA.2.75.

Explaining it further, Dr John said Alpha, Beta, Gamma and Delta variants came from the original Wuhan virus. Molecular virologists found that these variants had only a couple of mutations from the main virus, and it is usually dependent on the time the virus has been in circulation. This is true for every variant except for Omicron, which appeared first in South Africa and Botswana in late 2021.

“Virologists found 16 or 17 variations on the spike protein. This is an unexpectedly large number of mutations, which should have taken 10 years of circulation if it had evolved like other variants. But Omicron did not have 10 years of circulation,” pointed out Dr John. It then became difficult for scientists to trace back the origin of this variant and continues to remain a mystery, because it is the most unusual variant, which is why the paper uses the term ‘deviant’ for Omicron, which is almost a new genotype of the virus.   

As a part of their study, they found that investigators in Finland had tested the susceptibility of the house mouse to all the variants, including the original virus. It was found that they were susceptible to only the Beta variant, which was originally found in South Africa. While mice are naturally susceptible to Beta variant, hamsters were naturally susceptible to the Delta VOC.

Without Omicron deviant, the world would already have been in the post-Delta endemic phase. The possibility of another rare occurrence due to a potential reverse zoonosis of SARS-CoV-2 is extremely unlikely. The study highlighted that genetic and ecological circumstantial evidence prompted the scientists to propose reverse zoonosis, circulation in rodent population and subsequent spread as a zoonosis in human subjects as the most probable theory of the evolution and emergence of Omicron VOC.

The differences between Omicron and other VOCs in virus–cell interactions have major implications. Earlier VOCs caused a multi-system disease with lungs as the primary and predominant target organ – with bilateral viral pneumonia and inadequate oxygenation of blood resulting in hypoxia; gastrointestinal involvement was common, but cardiac, renal and neurological involvement was less frequent. A larger proportion of those infected needed hospital admissions, and mortality was high in the elderly and vulnerable, particularly men.

However, Omicron-induced disease is milder, with predominantly upper respiratory symptoms and far less severe lung disease overall; multi-system involvement is mostly absent. In short, Omicron-induced illness resembles the ‘common cold’, and most patients recover over 3–7 days. There is abundant
viral shedding from the upper airways and even in saliva leading to air-borne transmission. Intra-family spread of infection, very common with the Delta variant, is nearly 100 per cent with Omicron, making the family the unit of infection rather than the individual, revealed the paper.

In early reports from China, the severe disease occurred in about 15 per cent of those infected, and 8 per cent needed ventilator support. In India, data from Maharashtra showed a CFR (case fatality rate) of 2.75 per cent during the first wave in 2020; 1.81 per cent during the Delta-driven second wave and only 0.1 per cent during the Omicron-driven third wave in January 2022.

The authors even queried whether the disease caused by Omicron should be called COVID-21, as it was different. Omicron is better able to evade immunity from prior infection or prior vaccination. Globally, all COVID-19 vaccines have performed much better against symptomatic infection due to all previous VOCs than against Omicron. In South Africa, when Omicron became the dominant circulating variant in hospitalised patients with COVID-19, vaccine effectiveness (VE) in subjects vaccinated with two doses was 93 per cent for Delta but only 70 per cent for Omicron.

Researchers from Hong Kong found that Omicron, compared to Delta, has 70-fold greater potential to infect bronchial mucosal cells than alveolar cells (the cell of the air sac of the lung). Bronchial mucosal cells secrete mucus in order to trap foreign objects in the airway.

Simplifying the paper, Dr John highlighted that SARS-CoV-2 virus was expected to mutate slowly like the polio virus, but Omicron had an extremely high number of mutations in a short time.

“This is the fastest spreading variant and has evaded immunity to a large extent. It infected almost everybody as it has common cold-like symptoms. Once this has happened, no one variant can survive unless that variant is stranger than Omicron. That is why we are saying this is the last of the pandemic,” added Dr John.