A novel SARS-CoV-2 variant, VOC 202012/01 (lineage B.1.1.7), emerged in southeast England in September 2020 and rapidly spread to become the dominant variant in the UK. It has since spread to at least 114 countries. The variant is more transmissible than preexisting SARS-CoV-2 variants, with a reproduction number (R) estimated to be 43-90% higher. This increased transmissibility is likely due to higher infectiousness, longer infectious periods, or multiple mechanisms. The variant has caused a surge in COVID-19 cases and deaths in England, with projections indicating that without stringent control measures and accelerated vaccination, deaths in 2021 would exceed those in 2020. The UK government implemented strict lockdowns and restrictions to mitigate the impact. The variant has also been detected in Denmark, Switzerland, and the US, with similar increases in transmissibility. The study used social contact data, mobility data, and genomic data to assess the spread of the variant. The findings suggest that the increased transmissibility of VOC 202012/01 is not due to geographical or demographic differences but is a characteristic of the variant itself. The study also found that the variant's severity is uncertain, with estimates ranging from a moderate decrease to a moderate increase in severity. The study highlights the need for effective control measures, including vaccination and non-pharmaceutical interventions, to mitigate the impact of the variant. The findings have important implications for public health policy and the management of the pandemic.A novel SARS-CoV-2 variant, VOC 202012/01 (lineage B.1.1.7), emerged in southeast England in September 2020 and rapidly spread to become the dominant variant in the UK. It has since spread to at least 114 countries. The variant is more transmissible than preexisting SARS-CoV-2 variants, with a reproduction number (R) estimated to be 43-90% higher. This increased transmissibility is likely due to higher infectiousness, longer infectious periods, or multiple mechanisms. The variant has caused a surge in COVID-19 cases and deaths in England, with projections indicating that without stringent control measures and accelerated vaccination, deaths in 2021 would exceed those in 2020. The UK government implemented strict lockdowns and restrictions to mitigate the impact. The variant has also been detected in Denmark, Switzerland, and the US, with similar increases in transmissibility. The study used social contact data, mobility data, and genomic data to assess the spread of the variant. The findings suggest that the increased transmissibility of VOC 202012/01 is not due to geographical or demographic differences but is a characteristic of the variant itself. The study also found that the variant's severity is uncertain, with estimates ranging from a moderate decrease to a moderate increase in severity. The study highlights the need for effective control measures, including vaccination and non-pharmaceutical interventions, to mitigate the impact of the variant. The findings have important implications for public health policy and the management of the pandemic.