Ziyad Al-Aly noticed that more and more patients were coming to his Missouri clinic with what he describes as an air of invincibility. It was March 2022, and these patients were vaccinated and boosted against COVID-19, and they also had recently recovered from an infection. In their minds, the combined immunity would shield them from further harm.
“I started thinking, is this really true?” says Al-Aly, chief of research and development at the Veterans Affairs St. Louis Healthcare System and a clinical epidemiologist at Washington University in St. Louis. Intrigued, he turned to the VA’s medical records database to find out.
Time has since made clear that there are cracks in the shield created by both natural and vaccine-induced immunity: Reinfection rates are rising with the emergence of the more infectious Omicron variant, with some people even reporting their third or fourth infection. Studies have also shown that the Omicron subvariants are more capable of evading previous immunity. (Why Omicron variants BA.4 and BA.5 are causing fresh U.S. outbreaks.)