symptomatic infection from the Delta variant, this translates into vaccine effectiveness of between 0% and 20% after two doses, and between 55% and 80% after a booster dose, the study added. "This study provides further evidence of the very substantial extent to which Omicron can evade prior immunity given by both infection or vaccination," study lead Professor Neil Ferguson said in ICL's statement. “This level of immune evasion means that Omicron poses a major, imminent threat to public health," he said.
The data analysed by Imperial College was based on 333,000 cases, including 122,062 of Delta and 1,846 which were confirmed as the Omicron coronavirus variant through genome sequencing.