Can Omicron push Covid to turn endemic?
It causes Covid-19 that evades a bit of host immunity, but limits clinical disease as is evident from the near lack of reports about severe infection attributed to the variant
The last week has seen a further spurt in the numbers of Omicron cases in countries outside of South Africa, raising concerns of a likely larger wave globally in the near future. More importantly, given the high transmissibility of the variant, public perception is fast swinging from hope to a gloomy start of the New Year. The question often asked is: Will the pandemic ever end?”
Even as Delta is the most prevalent variant globally today, Omicron is fast catching up and may account for more infections than Delta very soon. Higher transmissibility of Omicron is expected because of the bulk of mutations occurring in the receptor-binding domain and near the furin cleavage site.
So why does Omicron spread so fast, but cause only mild symptoms? Two studies have thrown much-needed light on this question.
Using human lung tissue, a team of researchers from Hong Kong performed experiments to show that the Omicron variant replicated about 70 times higher in the human bronchus than the original Sars-CoV-2 virus strain and the Delta variant, thus making it several-fold more transmissible. On the other hand, it replicated with much less efficiency (more than 10 times lower) in human lung tissue than the original Wuhan strain, which may suggest lower severity of the disease.
The second study has come from the University of Cambridge, United Kingdom (UK) where the researchers found that the Omicron variant not only had a significantly high impaired ability to enter into lab-grown lung cells but was also not able to attract individual lung cells to fuse, much like a giant web or syncytium, a property exhibited by the Delta variant. Clinically speaking, efficient infection of lung cells by the virus is correlative of severe disease, and lower ability could make Omicron a milder variant.
Even though Omicron has so far caused milder clinical disease in over 89 countries that it has already spread to, immune escape from vaccines and past infection are areas of concern. A close look at the growing Omicron numbers suggests that there is a definitive population variation in its overall spread.
For example, the UK has been consistently recording 80-90,000 cases each day for the past one week despite 70% of its population having been fully vaccinated and 40% getting a booster shot. A study (with a very small sample) from the Imperial College, London, suggests that the risk of reinfection with the Omicron coronavirus variant is 5.4 times higher than for Delta, which means that the mutant virus could evade immunity conferred by both infection or vaccination, thus posing a major threat to public health.
Similar data has come from South Africa, which is reporting increasing cases of reinfection and of mild breakthrough infections in people who are vaccinated. The country witnessed a whopping 255% rise in Covid-19 cases last week and a test positivity rate of over 30%. However, most had milder disease and only 1.7% of required hospitalisation during the Omicron-driven fourth wave, compared with 19% in the same period during the Delta wave. Fully vaccinated people are likely to have a much lower risk of severe illness from Omicron infection. However, despite claims by manufacturers, there is still no peer-reviewed evidence on the efficacy of individual vaccines against Omicron.
India seems to be far better placed with nearly 64% of an estimated 940 million adult population having been fully vaccinated and another 28% with a single dose of either Covishield or Covaxin. Yet there are nearly 108 million adults that remain unvaccinated as of December 22 and that is not a small number. Our priority should be to target and fully vaccinate as much of the adult population as possible, while the boosters can wait.
There is no need to panic in the wake of the Omicron threat since the numbers are still low in India. It may be wise to save our boosters for the future, should there be another variant on the horizon that may turn out to be both highly transmissible as well as more pathogenic, causing a trail of destruction like Delta did in India.
A highly transmissible variant like Omicron that causes only mild infection should indeed be welcome. It causes Covid-19 that evades a bit of host immunity, but limits clinical disease as is evident from the near lack of reports about severe infection attributed to the variant. Since a complete eradication of Sars-CoV-2 is out of the question, variants such as Omicron could take us nearer to the realistic goal of the pandemic becoming endemic.
Nevertheless, it is important to slow down the spread and thwart the overall threat because even though the variant is less pathogenic, rapidly doubling numbers due to its higher transmissibility could put pressure on community immunity, leading to more severe disease in a fraction of the cases, and putting an avoidable load on hospital infrastructure.
India is home to yoga and meditation. A large-scale genomic study from researchers in the United States and published in PNAS on December 21 highlights the importance of these practices for enhancing the weakened immune system without activating inflammation. This coupled with the public health measures of maintaining virus-appropriate behaviour, avoidance of crowded spaces and getting vaccinated could be our best strategy to thwart new variants.
Dr Narinder Kumar Mehra is the honorary emeritus scientist of the Indian Council of Medical Research and former dean of the All India Institute of Medical Sciences, New Delhi
The views expressed are personal