Explainer | Omicron Subvariant, Waning Immunity: What's Driving Covid-19 Spike In India Again?

A steady spike in Covid019 cases across several states in India has left authorities concerned about the possibility of a fourth wave. On Monday, the country logged 12,781 fresh infections, pushing the daily positivity rate past 4 percent after 130 days. The rise in cases has also pushed up the total Covid-19 rally to 4,33,09,47 and 18 new deaths have taken the death toll to 5,24,873. On Monday, union health ministry data showed that there were 76,700 active cases across the country. As per data on June 18, 10 states and Union territories -- Maharashtra, Kerala, Delhi, Karnataka, Tamil Nadu, Haryana, Uttar Pradesh, Telangana, West Bengal and Gujarat -- have over 1,000 Covid cases.

But what is driving this spike in Covid-19 cases over the past four months?

Omicron sub-variants

According to experts at the Indian SARS-CoV-2 Genomics Consortium (INSACOG), Omicron and its sub-lineages -- primarily BA.2 and BA.2.38 as of now -- seem to be behind the current rise in the number of Covid cases in the country. 

BA.2 and its sub-lineages account for over 85 per cent of the Covid cases in India, with BA.2.38 being found in around 33 per cent of the samples. BA.4 and BA.5 are found in less than 10 percent samples. 

The states and Union territories have been asked to submit a "larger number" of samples for whole genome sequencing from the districts and areas that have seen a surge in Covid-19 cases over a period of seven days.

The direction was issued on Friday during a meeting of the INSACOG, which reviewed the Covid data to check the possibility of any new emerging variant or sub-variant and ascertain the reasons behind the breakthrough infections.

BA.2 and its sub-lineages account for over 85 per cent of the Covid cases in India, with BA.2.38 being found in around 33 per cent of the samples.

BA.4 and BA.5 are found in less than 10 per cent samples, as per INSACOG, which is trying to "keep a closer watch over the current circulating sub-lineages of Omicron and its correlation to the current epidemiological picture".

The experts are also trying to look for missing any important clues regarding newer sub-variants during routine sequencing through the sentinel surveillance.

Low natural immunity causing reinfections?

Some experts are of the opinion that the rising number of reinfections in states like Maharashtra may be due to the low immunity that Omicron a bout of creates in a body. A study published in Nature journal in May stated that infection with the Omicron variant of SARS-CoV-2 provides little long-term immunity against other variants in unvaccinated people. In experiments using mice and blood samples from donors who were infected with Omicron, researchers at Gladstone Institutes and University of California, San Francisco (UCSF) in the US found that the Omicron variant induces only a weak immune response. As opposed to Omicron, the Delta variant which preceded Omicron created a stronger natural immunity upon infection.

In vaccinated individuals, this response — while weak — helped strengthen overall protection against a variety of COVID-19 strains.

Waning vaccine immunity?

The reluctance among people towards following Covid-appropriate behaviour, in addition to many not being enthusiastic about taking the precaution dose of the vaccines, has possibly increased the pool of susceptible population. According to health experts, although there is a rise in the number of Covid cases, there is no associated increase in hospitalization or deaths. Also, the increase is limited to a few districts.

As per the World Health Orgnanisation, the immunity provided by vaccines does wane over time and that is why it is "critical to take more than one dose". On May 24, Union Health ministry data showed that less that 3.3 crore people had taken the booster shot.

The cumulative Covid-19 vaccine doses administered in the country crossed 196 crore on Saturday, the Union health ministry said. So far, over 3.57 crore children in the age group of 12-14 years have been administered the first dose while more than 6 crore adolescents in the age group 15-18 years have been given the first dose. As of now, only about 69 percent of the population is fully vaccinated.

Increased travel

In addition, there is an increased mobility due to summer holidays, easing of travel restrictions -- both nationally and internationally -- and the full-fledged opening up of economic activities, because of which the infection has spread among vulnerable individuals.

(With inputs from PTI)