The study estimates the transmissibility and impact of the SARS-CoV-2 variant of concern (VOC) 202012/01 (lineage B.1.1.7) in England. The variant, first detected in southeast England in September 2020, rapidly became the dominant lineage and has spread to at least 144 countries. Using social contact and mobility data, demographic indicators, and mathematical models, the researchers found that the new variant has a 43 to 90% higher reproduction number (R) compared to preexisting variants. This increase in transmissibility is consistent across different regions and countries, including Denmark, Switzerland, and the United States. The study also assessed the severity of disease associated with the new variant but found no clear evidence of increased or decreased severity. The researchers projected that without stringent nonpharmaceutical interventions and an accelerated vaccine rollout, COVID-19 hospitalizations and deaths in England in the first half of 2021 would exceed those in 2020. The findings highlight the urgent need for effective control measures to mitigate the impact of the new variant.The study estimates the transmissibility and impact of the SARS-CoV-2 variant of concern (VOC) 202012/01 (lineage B.1.1.7) in England. The variant, first detected in southeast England in September 2020, rapidly became the dominant lineage and has spread to at least 144 countries. Using social contact and mobility data, demographic indicators, and mathematical models, the researchers found that the new variant has a 43 to 90% higher reproduction number (R) compared to preexisting variants. This increase in transmissibility is consistent across different regions and countries, including Denmark, Switzerland, and the United States. The study also assessed the severity of disease associated with the new variant but found no clear evidence of increased or decreased severity. The researchers projected that without stringent nonpharmaceutical interventions and an accelerated vaccine rollout, COVID-19 hospitalizations and deaths in England in the first half of 2021 would exceed those in 2020. The findings highlight the urgent need for effective control measures to mitigate the impact of the new variant.