The World Health Organisation on Saturday urged South Asian countries including India to scale up surveillance, strengthen public health measures and expand vaccine coverage, cautioning about Covid-19 surges elsewhere and a new variant of concern.

The WHO’s Southeast Asia regional office said these countries must enhance surveillance for Covid-19 and increase genome sequencing of coronavirus samples even though Covid-19 cases were declining in most countries in the region.

The appeal, directed at a region where hundreds of millions of people are yet to be vaccinated, comes amid concerns triggered by the highly mutated B.1.1.529 variant that has spread fast in South Africa and turned up in several other countries including the UK. The WHO named the variant “omicron” on Friday.

“The earlier the protective measures are implemented, the less restrictive they would need to be in order to be effective,” Poonam Khetrapal Singh, regional director of WHO Southeast Asia region, said. She called for comprehensive and tailored public health and social measures to prevent transmission.

Singh said 31 per cent of the Southeast Asia region’s population had been fully vaccinated as of Saturday, while nearly 48 per cent or about a billion people were yet to receive even a single dose of a Covid-19 vaccine. They continue to be at risk of developing severe Covid-19 and spreading the virus.

Experts guiding India’s surveillance and sequencing efforts said on Saturday that health authorities in states across the country should be looking out for any unusual clusters of cases and rapidly sequence samples if such spikes emerged.

“This is what we should be doing anyway,” said a medical expert in a central government lab involved in sequencing coronavirus genomes. “What we need is heightened awareness across the health system and among the public.”

Scientists are worried about omicron because it has an unusually large set of mutations that appear to make the virus stronger against the human immune system than any of the earlier known variants.

The health ministry had earlier this week directed the states to enhance surveillance and continue to screen travellers arriving in India, with special requirements for travellers from “high-risk” countries, including those where omicron has turned up.

Sections of public health experts believe that India’s response thus far has been measured in contrast to the actions of several other countries that have blocked travel from South Africa and other nations where omicron has emerged.

Omicron has so far been reported from Botswana, South Africa, Hong Kong, Israel, Belgium and the UK. Authorities in Germany and the Czech Republic have also said they have suspected cases. But experts believe the virus has likely already spread to other countries and will get detected only through high-quality surveillance and genome sequencing.

“Imposing travel restrictions and restricting entry from a few countries is not going to help either prevent or control the spread of omicron,” Giridhar Babu, a public health specialist in Bangalore, tweeted. “It is akin to closing the stable door after the horse has bolted.”

Instead, Babu wrote, health authorities should be looking out for clusters of cases of recent origin.