I am so old, I remember when The Expertstm said natural immunity did not exist (which never made any sense):
Three years into the pandemic, the immune systems of the vast majority of humans have learnt to recognize SARS-CoV-2 through vaccination, infection or, in many cases, both.
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In one study1, researchers looking at Portugal’s national database of infections studied vaccinated people who became infected during the BA.1/BA.2 wave. Analysis showed that 90 days after an infection, this population had high immune protection — their risk of becoming infected with BA.5 was just one-sixteenth that of people who had been vaccinated but never infected. After that, hybrid immunity against infection declined steeply for a few months and then stabilized, ultimately providing protection for eight months after infection, the duration of the study.
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What about those who haven’t been vaccinated? Another study in Qatar suggests that if the virus doesn’t change, infection-based immunity against reinfection can last up to three years.
Source: How quickly does COVID immunity fade? What scientists know
