The pharmaceuticals company Moderna has said a booster dose of its Covid vaccine appeared to protect against the fast-spreading Omicron variant in laboratory testing and that the current version will continue to be its “first line of defence against Omicron”.

The decision to focus on the current vaccine, mRNA-1273, was driven in part by how quickly the variant is spreading. The company plans to develop a vaccine specifically to protect against Omicron, which it hopes to advance into clinical trials early next year.

Dr Paul Burton, Moderna’s chief medical officer, said: “What we have available right now is 1273. It’s highly effective and extremely safe. I think it will protect people through the coming holiday period and through these winter months, when we’re going to see the most severe pressure of Omicron.”

The company said a two-dose course of its vaccine generated low neutralising antibodies against Omicron but a 50µg booster dose increased neutralising antibodies against the variant 37-fold. A higher, 100µg booster dose of the same vaccine drove antibody levels even higher – more than 80 times pre-boost levels.

The data, which has not yet been peer reviewed, tested blood from people who had received the vaccine against a pseudovirus engineered to resemble the variant. It is similar to data discussed by the top US infectious disease expert, Dr Anthony Fauci.

Burton said it would be for governments and regulators to gauge whether they wanted the enhanced level of protection that a 100µg dose might confer.

The company said the 100µg dose was generally safe and well tolerated, although there was a trend toward slightly more frequent adverse reactions.

Moderna also tested the vaccine’s effectiveness compared with its prototype boosters that target multiple previous variants of concern and the results were similar.

US regulators authorised the 50µg booster of Moderna’s vaccine in October. The first two shots are both 100µg.

The Moderna and the Pfizer/BioNTech vaccines have been linked to rare cases of heart inflammation, particularly in young men. Several studies have suggested Moderna’s vaccine is likely to cause that side-effect at a higher rate.

Omicron, a highly contagious variant first detected last month in southern Africa and Hong Kong, has raced around the world and been reported in 89 countries, according to the World Health Organization.

It said the number of Omicron cases was doubling in one and a half to three days in areas with community transmission, but noted that much remained unknown about the variant, including the severity of the illness it causes.

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