New variantsThe B.1.1.7 variant that has become predominant in the UK and is expected to take over soon in the US has been estimated to be 30% to 70% more transmissible than the version of the SARS-CoV-2 virus we have come to know and heartily dislike.
Because of the magic of exponential growth, this can translate into a greater than 30%-to-70% increase in the number of cases in just a few weeks.What seems like only a moderately higher growth rate can bring many, many more cases in short order.
In the real world, as in the susceptible-exposed-infectious-recovered (SEIR) models that epidemiologists use, the growth rate does at least slow over time as people become immune and change their behaviour to avoid the disease.