this again? learn
memory T-cells!
https://www.cebm.net/covid-19/what-...n-why-immunity-is-about-more-than-antibodies/
potential for long-term immunity
Early research suggests that the antibodies in people infected with SARS-CoV-2 dropped significantly within 2 to 3 months [21,22], causing concern that humoral immunity against the virus may decline rapidly. However, it is a normal part of the immune response that antibody levels fall after an infection has resolved [23]. For example, in seasonal coronavirus infections, antibodies start to decline at about a week after infection and typically only last for about a year [24]. It should also be noted that memory T and B cells are formed after infection [25,26]; these can be reactivated when another infection with the same virus occurs and could provide long-lasting immunity.
A preliminary study that has not yet undergone peer review has shown that memory T and B cells were found in patients with mild COVID-19 symptoms who had recovered and that these cells persisted, suggesting the potential for longer-term immunity [27].
SARS-CoV-2-specific memory T cells have also been detected in exposed seronegative healthy individuals (relatives of confirmed cases), which may indicate asymptomatic infection. One study has shown that ~93% of “exposed asymptomatic” individuals had a T cell response to SARS-CoV-2, despite seropositivity in only 60% of cases [28]. Asymptomatic infections may therefore be more common, and antibody testing alone may underestimate the true prevalence of the infection or population immunity.
SARS-CoV-2-specific T cells were found in most of the convalescent patients in this study, which is a promising sign that infection may give rise to immunity [29]
