One idea is that Covid may be altering our immune systems.
Malgorzata Gasperowicz, a Calgary based developmental biologist, says that if immunity debt fully explained rising infection counts we’d expect to see a uniform rebound across all pathogens. But we don’t, she says.
For instance, a 2024 study of more than 4000 viral cases from Ontario, Canada,4 found higher rates of bacterial infections in people recovering from covid-19 than in those recovering from influenza or RSV—although study groups weren’t perfectly matched by age or clinical setting, limiting direct comparisons.
Jeimy says that many infants and toddlers admitted to hospital with rare infections since 2022 weren’t yet born when pandemic restrictions were in place, and they therefore couldn’t be experiencing immunity debt. They were, however, likely exposed to SARS-CoV-2.
Wolfgang Leitner, chief of the Innate Immunity Section at the US National Institute of Allergy and Infectious Diseases (NIAID), speculates that covid-19 may somehow impair the immune system’s “memory” of past infections, potentially making even healthy people more vulnerable to future pathogens. He wonders whether the virus leaves lasting scars on the immune system’s T cell defences. “But that’s just (my) hypothesis,” he emphasises in an email.