Increased household transmission and immune escape of the SARS-CoV-2 Omicron variant compared to the Delta variant: evidence from Norwegian contact tracing and vaccination data

We compared the secondary attack rate (SAR) of the SARS-CoV-2 Omicron and Delta variants in households using contact tracing data. Omicron SAR was higher (41%) than Delta (35%), likely due to immune evasion. Booster dose reduces risk of infection but has limited effect on preventing Omicron transmission.