In the winter, COVID-19 cases shot up and plummeted with unprecedented speed. But experts say something else is going on with this surge. So far, the immunity many people acquired then has helped to dampen the spread of the two forms of Omicron powering the current, stretched-out wave of cases. "It's imperfect, but it's at least some protection," said Dr. Joe Gerald, an associate professor of public health policy at the University of Arizona's Mel and Enid Zuckerman College of Public Health.