Moderna Inc said on Monday that a booster dose of its Covid-19 vaccine appeared to be protective against the fast-spreading Omicron variant in laboratory testing and that the current version of the vaccine would continue to be Moderna’s "first line of defence against Omicron".

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