> But if you look at how influenza stopped spreading almost completely the last year and a half you have to conclude that either unfit masks with gaps do help s

> But if you look at how influenza stopped spreading almost completely the last year and a half you have to conclude that either unfit masks with gaps do help significantly versus respiratory viruses, or, sampling for influenza cases has been borked due to the overloading need to test for sars-cov-2. I think it's three effects: (1) Acute infection with respiratory virus X is protective against respiratory virus Y. This is because of the cellular interferon response (see https://pubmed.ncbi.nlm.nih.gov/778995/); https://pubmed.ncbi.nlm.nih.gov/778995/); basically the non-specific component of the immune system gets "revved up" and thus subsequent pathogens don't stand a chance. This might be further accentuated by the fact that SARS-2 specifically can acutely downregulate interferon response (see https://www.biorxiv.org/content/10.1101/2020.08.16.252973v1 https://www.biorxiv.org/content/10.1101/2020.08.16.252973v1), presumably to suppress the immune response against it, which would/could lead to a rebound upregulation in interferon after the initial phase of SARS-2-mediated interferon suppression (2) Some people who actually had Influenza would have tested for COVID first, and been PCR positive because the PCR tests in the real world can stay positive for a couple months after resolution of the infection (due to the absurdly high cycle threshold that is often used). This is what you said, I'm just elaborating a bit more on how it actually happens (3) Influenza spreads less easily than SARS-2, so it's possible the NPIs had some effect. This is my least favorite theory because the NPIs were so poor against SARS-2 and measures like school closures haven't been shown to reduce Influenza. My guess is stuff like people avoiding family members during 2020 holidays etc did decrease the connections between social nodes a bit, so there was some effect but not a huge one from the altered behavior