This is the strongest evidence so far that shows sustained defence in people who have recovered from coronavirus. This study shows that #COVID19 recovered people show faster and stronger immune response upon re-infection.
Study: Evolution of Antibody Immunity to SARS-CoV-2 (Biorxiv, 7 Nov 2020)
 What we knew till now?
Antibody levels decrease with time. (3 to 6 months)
 What was NOT studied till now?
The nature and quality of the memory B cells that would be recruited to produce antibodies upon re-infection.
 What did this study show?
(a) #SARSCoV2 B cell immune memory not only perseveres but evolves in a way that suggests protection from re-infection. This happens proportional to antigen/ virus persistence.
(b) Antibody evolution occurs in germinal centers in the immune system, where antigen can be retained in the form of immune complexes for prolonged periods of time.
(c) Residual virus in tissues (eg. gut) represents another potential source of antigen.
 Main findings:
(a) Antibody levels and antibody neutralizing activity decreased 6 months after infection. (expected and known)
(b) However, memory B cells, the type of cells that are responsible for rapid antibody production upon re-infection, were stable and even slightly increased in number.
 Practical implications:
(a) Memory B cell responses did not decay up to 6 months after SARS-CoV-2 infection – optimistically suggests protection from re-infection upon re-exposure to SARS-CoV-2.
(b) It suggests that recovered #COVID19 patients mount a much faster and more effective defence against the infection if they encounter the virus again.