As new omicron sub-lineages continue to spread in other countries, India’s surveillance network has detected the XE variant in only two cases over the past month with no impact on the course of the country’s Covid-19 epidemic yet.

The nationwide consortium of labs tasked with sequencing coronavirus genomes has confirmed XE in one sample from Mumbai on March 2, the other from Vadodara on March 12, a top official coordinating the sequencing efforts said on Tuesday.

Epidemic patterns in the UK have suggested that XE — a recombinant or mixed virus with sequences from two omicron sub-lineages called BA.1 and BA.2 — has a 12.6 per cent growth advantage over BA.2, the currently dominant variant in many countries, including India.

But medical experts say XE has not had any visible impact on the local epidemics in Mumbai, Vadodara or elsewhere in the country in the month since the first case. The Union health ministry had last week flagged slight increases in test positivity rates in Gujarat and Maharashtra and three other states during the previous week, but experts believe the rise was due to increased interactions without masks.

“There is absolutely no change in either the course of the epidemic or severity of the infection,” said Rahul Pandit, director of critical care medicine at Fortis Hospital, Mumbai, and member of Maharashtra’s Covid-19 task force. “There is no doubt we have a high level of population immunity acquired through the vaccination coverage and through the three earlier Covid-19 waves.”

“But we need to maintain vigilance — new variants are likely to keep coming,” he said.

Several countries have documented new sub-lineages of omicron. An April 8 technical briefing paper from the UK Health Security Agency said an omicron sublineage called BA.4 has been identified

in South Africa (in 45 samples), Denmark (3), Botswana (2), Scotland (1) and England (1).

South Africa has also submitted 27 samples of another sub-lineage called BA.5 that shares the same mutations as BA.4 except certain differences that make it eligible to be labelled a new sub-lineage.

Virologists say new variants will continue to emerge as long as the coronavirus gets opportunities to infect people and multiply. But, they say, India’s high vaccination coverage — over 84 per cent of adults are fully vaccinated — and large proportion of people with a history of Covid-19 infections will shield the population from severe disease.

“Will the virus change so much that our immune system won’t recognise it anymore — unlikely, but we don’t know,” said a clinical virologist.

India’s counts of average daily new infections have continued to fall over the past month — the seven-day average of daily new cases has decreased from 4,005 on March 12 to 1,013 on April 12.