Clinical, virological and immunological features of a mild case of SARS-CoV-2 re-infection.

Abstract Objectives We report a case of SARS-CoV-2 reinfection 6 months after the first infection in a young healthy female physician. Both episodes led to mild COVID-19. Methods SARS-CoV-2 infections was detected by RT-PCR on naso-pharyngeal specimens. Reinfection was confirmed by whole-genome sequencing. Kinetics of total anti-S receptor binding domain immunoglobulins (Ig anti-S RBD), anti-nucleoprotein (anti-N) and neutralizing antibodies were determined in serial serum samples retrieved during both infection episodes. Memory B cells responses were assessed at day 12 post reinfection. Results Whole-genome sequencing identified two different SARS-CoV-2 genomes both belonging to clade 20A, with only one non-synonymous mutation in the spike protein, and clustered with viruses circulating in Geneva (Switzerland) at the time of each of the corresponding episodes. Seroconversion was documented with low level of total Ig anti-S RBD and anti-N antibodies at one month after the first infection whereas neutralizing antibodies quickly declined after the first episode and then were boosted by the reinfection, with high titers detectable 4 days after symptoms onset. A strong memory B cell response was detected at day 12 post onset of symptoms during reinfection, indicating that the first episode elicited cellular memory responses. Conclusion Rapid decline of neutralizing antibodies may put medical personnel at risk of reinfection as shown in this case. Reinfection however leads to a significant boosting of previous immune responses. Larger cohorts of reinfected subjects with detailed descriptions of their immune responses are needed to define correlates of protection and their duration after infection.