A three-dose course of AstraZeneca's Covid-19 vaccine is effective against the Omicron coronavirus variant, the pharmaceutical company said, citing data from an Oxford University lab study.

The study, yet to be published in a peer-reviewed medical journal, showed antibody levels against Omicron after the booster shot were higher than antibodies in people who had been infected with and recovered naturally from Covid-19, Reuters reported.

After a three-dose course of the vaccine, neutralising levels against Omicron were similar to those against the virus's Delta variant after two doses, the company added.

The Anglo-Swedish drugmaker said researchers at Oxford University who carried out the study were independent from those who worked on the vaccine, Vaxzevria, with AstraZeneca.