A three-dose course of AstraZeneca's Covid-19 vaccine is effective against the rapidly-spreading omicron variant, the pharmaceutical company said on Thursday, citing data from an Oxford University study.

       Findings from the study, yet to be published in a peer-reviewed medical journal, match those from rivals Pfizer-BioNTech which have also found a third dose of their shots works against the variant.

       The study on AstraZeneca's vaccine, Vaxzevria, showed that after a three-dose course of the vaccine neutralising levels against omicron were broadly similar to those against the virus's delta variant after two doses.

       The company said that researchers at Oxford University who carried out the study were independent from those who worked on the vaccine with AstraZeneca.

       "As we better understand omicron, we believe we will find that T-cell response provides durable protection against severe disease and hospitalisations," Mene Pangalos, the head of AstraZeneca's biopharmaceuticals research and development said, referring to a critical component of the immune system that responds to fight infection.

       Antibody levels against omicron after the booster vaccine were higher than antibodies in people who had been infected with and recovered naturally from Covid-19, the Anglo-Swedish company added.

       Although the early data is positive for the company, AstraZeneca said on Tuesday it was working with its partner Oxford University to produce a vaccine tailored for omicron, joining similar efforts from other vaccine-makers.

       The Oxford study analysed blood samples from those infected with Covid-19, those vaccinated with two doses and a booster, and those previously infected with other variants of concern. It included samples from 41 people given three doses of Vaxzevria.

       Separately, Novavax also revealed that its Covid vaccine is effective in generating an immune response against omicron, according to early data published on Wednesday.

       "We are encouraged that boosted responses against all variants were comparable to those associated with high vaccine efficacy in our Phase 3 clinical trials," said Gregory M. Glenn, Novavax's president of research and development.