Omicron to displace Delta as dominant strain: ICMR study

With the spread of the Omicron variant, which is now in community transmission in India, the Delta variant will fade away, according to the latest study of the Indian Council of Medical Research.

The ICMR study analyses the IgG and neutralising antibodies (NAbs) against the B.1, Alpha, Beta, Delta and Omicron variants, with the sera of individuals infected with the Omicron variant. It shows that individuals infected with Omicron have a significant immune response, which could neutralise not only the Omicron, but other variants of concern, including the most prevalent Delta variant.

“This suggests that the immune response induced by Omicron could effectively neutralise the Delta variant, making re-infection with the variant less likely, thereby, displacing Delta as the dominant strain. This emphasises the need for an omicron specific vaccine strategy,” says the study report by ICMR-NIV, Pune, conducted under the project titled ‘Assessment of immunological responses in breakthrough cases of SARS-CoV-2 in post COVID-19 vaccinated group.

These findings are in complete contrast to other studies which have suggested that the immune response generated through natural infection or vaccination was weaker against Omicron. The variant has shown higher transmissibility and immune escape as against other VOCs, including Alpha, Beta, and Delta, leading to many reported breakthroughs and re-infections across the globe. However, the severity of the disease is lesser as observed with other VOCs, says the report.

The study was conducted on 39 individuals with a history of foreign travel. The participants were grouped into three categories - breakthrough infections after two doses of Pfizer (8), those vaccinated with Covishield (25) and unvaccinated (6). 

The mean age of the Covishield vaccinated individuals was 39 years, with 13 being asymptomatic, and 12 having mild fever, a sore-throat, and cold and cough lasting for one to three days. Of these, two cases were of reinfection with documented past infection in July 2020. The individuals vaccinated with two doses of Pfizer had a mean age of 33 years and only one case was reported to have mild fever and a sore throat, while the remaining seven were asymptomatic. Of the unvaccinated group of six, all females with a mean age of 16 years, five were pediatric and one was adult. Of these, four were asymptomatic, while two pediatric cases were mildly symptomatic. 

ICMR study not enough: Jacob John

India’s renowned virologist T Jacob John said there is a possibility that the Omicron variant may displace the Delta variant. However, he saidthe ICMR study is not enough to predict this and further research needs to be done.

“Omicron is not easily neutralised by antibodies made against other variants or vaccines. But antibodies made by the body in response to Omicron are just like other viruses. So those who have got infected with Omicron will be better protected against Omicron and Delta. Therefore, it is possible that Omicron immunity will overshadow Delta, but both could remain in human beings also. Because there are a lot of people who don’t get infected with Omicron, they may be getting infected with Delta,” said John, who is a retired professor and Head of the Departments of Clinical Virology and Microbiology at CMC Vellore

.“INSACOG should study this as this ICMR study is not enough to predict. They need to look at regular sampling of viruses, full genome analysis and the proportion of Omicron and Delta variants. They need to see whether the variants are emerging, these are the questions they need to answer,” John said.

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