主要是因為有了 immune imprinting

所以再染疫後果相對輕一些。

Immunological imprinting is a phenomenon where prior exposure to a viral strain (an antigen) elicits B-cell memory which confers protection against related antigens in the future. In other words, first exposure to an antigen (e.g., a viral pathogen) leaves an ever-lasting 'imprint' on the naïve immune system.