White blood cell counts may be off, immune cells don’t work the way they should, inflammation is higher than it should be. “Long story short, COVID-19 leads to lasting, and possibly permanent changes in immune cells in some, but not all, people,” McMaster University immunologist Dawn Bowdish said.

Research is suggesting that T cells, the cells that help produce antibodies and kill infected cells, are taking a particular hit, and that repeated SARS-CoV-2 infections may be prematurely aging human immune systems.

The scale isn’t yet clear. However, “a potential increase in acquired impaired immunity in the Ontario population could have significant impact on the incidence and associated burden of infectious diseases ….and other conditions in the longer-term,” reads the Public Health Ontario evidence brief.

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The concern is that people will be less able to hold off future bugs and pathogens like influenza, or that unsettled immune systems could lead to an increase in diabetes and other auto-immune diseases.