It was established pretty firmly by the end of 2021 or early 2022. There was even at least one site that gamified it, by showing graphs of infections/deaths for similar US states and similar European countries and having you guess which ones did/didn't do various measures (lockdowns, masks, etc) or having you guess at what point in time they were instituted/repealed. None of it had any effect. IIRC the only real visible patterns involved latitude, time of year, and average population age. It's just really hard for most people to accept just how much their lives were disrupted from lies (if they ever even encountered the truth).