Simple answer: Variants are more contagious.
For example, a new report out today based on Canadian data from Ontario concluded that “compared to people infected with less contagious coronavirus variants, those infected with the variant identified in the UK, known as B.1.1.7, are more likely infect their household members”.
More specifically, the secondary infection rate was 31% higher when the patient was infected with the B.1.1.7 virus variant than compared to “a less worrisome variant”, a rate that was 200 % higher in family contacts when the infected person with the variant had no symptoms but became ill with symptoms later on.
Bottom line: Vaccinate more people. More quickly. Starting today.