Omicron sub-variant BA.2.75 dominant in Delhi; caution advised for those with low immunity, underlying diseases 

(Image: AFP)

The national capital has been in the headlines for the last three weeks for recording the highest daily tally of COVID-19 cases and test positivity rate in the country.

Top officials and scientists with the COVID-19 genomic surveillance programme, INSACOG, said the latest increase in Delhi's tally has been caused by Omicron sub-variant BA.2.75, now the most dominant SARS-CoV 2 strain circulating in the city.

The strain, first detected in Maharashtra in May this year and sometimes referred to as Centaurus, is spreading faster than other Omicron sub-variants such as BA.5, which has been responsible for a rise in COVID-19 cases in countries such as the US over the last couple of months.

Delhi has been registering daily new infections upwards of 1,000 and the city’s test positivity rate has risen to 18 percent, triggering alarm in the health administration.

In the past week, the city also registered 52 deaths, the highest since January this year, when the third COVID-19 wave, driven by the Omicron variant, hit India.

“In many parts of India, BA.2.75 is the dominant SARS CoV 2 strain now and it has strong characteristics of causing quick transmission and breakthrough infections even in those fully vaccinated,” said a senior scientist attached with INSACOG.

This sub-variant was detected in about 50 percent of the samples that were subjected to whole genome sequencing last week but the scientist added that its percentage share varied from state to state.

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India on August 17 reported 9,062 new coronavirus cases and 36 deaths, which included six previously unreported deaths.

Dr Sujeet Kumar Singh, director of the National Centre for Disease Control, which heads INSACOG, told Moneycontrol, “We need to analyse why each of these deaths is happening; whether this is specifically because of COVID-19, but there is no reason for concern as yet.”

Immune-escape properties

Senior virologist Dr Gagandeep Kang said the surge in cases may be because the sub-variant escapes the immune response sufficiently to be able to infect people. Yet, the number of hospitalisations is limited because the infection is not severe.

“We should not worry at the moment unless we have extra vulnerability, such as the elderly and high number of patients with cancer, transplant,” she said.

According to Kang, higher risk groups should get COVID-19 booster doses if they have not done so already.

“Boosters do not give perfect protection, but do reduce risk of severe disease,” she said.

Epidemiologist Dr Naman Shah said although the reasons for the higher number of COVID-19 deaths, when compared to previous weeks, may be difficult to assess without analysing clinical data, it may have something to do with waning immunity among the elderly or misclassification.

“For example, some patients may have died for another reason but happened to be COVID-19 positive,” he said.

Corbevax the solution?

Biologist Dr Anurag Agarwal, who was previously been associated with the Council for Scientific and Industrial Research-Institute for Genomics and Integrative Biology (CSIR-IGIB) in New Delhi, said the low-level surge in COVID-19 cases and deaths was not unexpected.

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“The vulnerable group, especially elderly with co-morbidities, must maintain precautions and get boosted,” he said.

According to Agarwal, approval for COVID-19 vaccine Corbevax as a booster dose offers a choice for such people.

Last week, the Union health ministry allowed the use of Corbevax, a protein sub-unit vaccine developed by Biological E, as a booster for all adults who may have been jabbed with Covaxin or Covishield earlier.

Many experts have said that Corbevax may be a superior choice for the recipients of the other two vaccines and may offer better protection against COVID-19 when compared to a homologous booster (same as the primary vaccine).