Data on secondary attack rates released on Saturday by a British public health agency similar to our own Centers for Disease Control and Prevention suggests that this variant first seen in India may be substantially more transmissible among close contacts than even the already highly transmissible B.1.1.7. A report published by the same agency on Thursday further supports last week’s findings. It was just such early data that raised alarms about B.1.1.7, with later information confirming those early fears. Adam Kucharski, an epidemiologist with the London School of Hygiene and Tropical Medicine, also told me that the faster spread in areas of Britain with higher levels of the variant suggests it has higher transmissibility. This point seems to be backed up by the terrible outbreaks in India and neighboring Nepal, where it is also widespread. Given how limited genetic identification is in those countries, the data from Britain is particularly useful for assessing the risk. A variant with higher transmissibility is a huge danger to people without immunity either from vaccination or prior infection, even if the variant is no more deadly than previous versions of the virus. Residents of countries like Taiwan or Vietnam that had almost completely kept out the pandemic, and countries like India and Nepal that had fared relatively well until recently, have fairly little immunity, and are largely unvaccinated. A more transmissible variant can burn through such an immunologically naïve population very fast.