Delta’s ‘descendants’ outdo even Delta in Mumbai samples

MUMBAI: It isn’t Omicron or Delta, but Delta’s descendants that are the common Covid-causing SARS-CoV-2 variants in circulation in Mumbai at the moment, according to results of BMC’s fifth genomic sequencing exercise released on Thursday.

The sequencing, carried out at BMC’s genetic laboratory in Kasturba Hospital, found the Delta variant in 11% of the 221 Covid-19 patients from Mumbai studied. The remaining 89% showed Delta Plus or A.Y.x sublineages and less than 1% (two cases) had Omicron.

In the four sequencing exercises carried out since August, Delta was most dominant, accounting for 70-80% of samples. “But now Delta derivatives appear to be more in circulation in Mumbai. The clinical symptoms of positive patients bear testimony to the fact that Delta is either getting weaker or the population has developed immunity against it,” said BMC additional commissioner Suresh Kakani. None of the 221 patients died, and most of the hospitalised patients had mild symptoms.

Experts said phasing out of the Delta variant isn’t surprising. “The proportion of Delta derivatives have been increasing steadily. We can state that the second wave has declined and only the unvaccinated are getting hospitalized,’’ said Dr Shashank Joshi, a member of the state government’s task force on Covid-19.

Vellore-based virologist Dr T Jacob John said the change is unlikely to affect the spread. Mumbai registers 150-200 cases daily. “Delta derivatives have, after all, come from the same base which is Delta. As is the nature of viruses, there are bound to be some mutations, but derivatives are unlikely to cause a huge shift,” he said.

Moreover, as the second wave in India was caused by the Delta variant, the majority have “sort of exposure” to the sub-lineages too, he added. However, Dr Rahul Pandit, another member of the state Covid-19 task force, said Delta derivatives weren’t totally harmless as his ICU in Fortis Hospital, Mulund still gets a few critically ill patients.

While Omicron had a tiny presence in the fifth genome sequencing exercise, experts believe it will slowly grow in proportion. “Delta will be replaced by Omicron steadily in weeks to come. Whether it will drive people to hospitals or cause mild illnesses remains to be seen,” said John.

Dr Joshi said, "The present Omicron cases in Mumbai and the rest of the country are related to travel. If and when the variants gets into the community, we will see newer trends. At present, there is no cause for panic.’’

Incidentally, only one of the 221 patients who received the first dose and only 26 fully vaccinated patients needed hospitalizations. Twelve of the 47 people who did not receive a single dose of the vaccine had to be hospitalized. Almost 64% of the patients were in the 21-60 age group, while 54 (25%) were in the 61-80 age group.