States with High Vaccination Rates Can Still Experience COVID-19 Surges — Here’s Why

“We went through the same cycle last year with different parts of the country… going up at different times,” Dr. Robert C. Bollinger, a professor of infectious diseases, medicine, public health, and nursing as well as director of the Center for Clinical Global Health Education at Johns Hopkins University School of Medicine in Baltimore, told Healthline.

“There are probably a number of factors contributing to the current spike,” Dr. Karen Edwards, chair of the department of epidemiology and biostatistics at the University of California, Irvine Program in Public Health, told Healthline. “Some of the most likely factors are that as the weather gets colder, more people are gathering indoors and in closer proximity to each other, which facilitates transmission between individuals.”

“There may also be less adherence to mask wearing, good hygiene, and social distancing, which combined with more indoor activities, will increase opportunities for infection, especially among the unvaccinated,” said Edwards.