The Indian SARS-CoV-2 Genomics Consortium said on Saturday that more scientific experiments are needed to assess the impact of booster doses of Covid-19 vaccines, a week after advising that it may be considered for people above 40 because of the new Omicron virus variant.

Booster shots are jabs given to ramp up the number of antibodies provided by vaccines that wane over a period of time.

In a bulletin dated November 29, the genome sequencing body had said: “Vaccination of all remaining unvaccinated at-risk people and consideration of a booster dose for those 40 years of age and over, first targeting the most high-risk/high-exposure may be considered, since low levels of neutralising anti-bodies from current vaccines are unlikely to be sufficient to neutralise Omicron.”

But in a document released on Saturday, the consortium said its earlier statement was “not a recommendation or suggestion for booster dose in the national immunisation program”.

The Omicron variant was first detected in South Africa in November and has appeared in nearly two dozen countries. So far, India has confirmed five cases of the variant. It is still not clear whether, or to what degree, Omicron may evade protection conferred by the vaccines.

The genome consortium said on Saturday that immunity and protection from Covid-19 is “multifactorial”.

“Many more scientific experiments are needed to assess the impacts of booster dose, which are being guided and monitored by National Technical Advisory Group on Immunisation and National Expert Group on Vaccine Administration for Covid-19,” it added. “The recommendations and suggestions regarding vaccines, schedule, and roll out comes under expressed mandate of NTAGI and the NEGVAC.”

The Centre has emphasised that its priority is to first vaccinate all eligible Indians with the first two doses of the vaccines. On Thursday, Lav Agarwal, joint secretary in the Union health ministry, had said that scientific rationale for administering booster doses was still under examination.

Almost 40 countries, mostly the rich and developed ones, are allowing citizens to get inoculated with a third vaccine dose.