The authors were doing follow-ups among 273 cases of COVID-19 from Beijing Diton Hospital, and they found 28 patients who tested positive for SARs-COV2 again.
The time interval between the primary infection and the beginning of reinfection was 19 to 57 days, and they had negative PCR results between episodes.
To determine which of those were true infections, they used MINERVA sequencing strategy on paired clinical specimens in first and second episodes and found 6 paired-genomes were attributed to different lineages, which was a strong evidence of true reinfection rather than false positive or relapse of primary infection.
The scientists further assessed the dynamics of antibody response by measuring specific IgM/IgG targeting the receptor-binding domain of S protein and N protein. They observed that 3 patients (P1, P3 and P6) with initially high antibody titers after recovery were able to maintain titers level above 1 : 160 into secondary infection. The question was why reinfection still occurred for those 3 patients even though they had measurable amount of neutralizing antibodies. They noted that 5 out of those 6 patients were reinfected with D614G viral variants, and the serum from these patients was still able to neutralize D614G in vitro, ruling out the possibilities of those mutations afford the virus immune escape capabilities.
Therefore, the authors questioned that whether a threshold level of antibody response is required for protection against the virus. Also, vaccine-induced immunity might be different from natural immunity, vaccines might not induce the same t cell responses as a true infection does. Essentially, they observed a decreased in CD4 T cell counts in 5 patients and CD8 in 2 patients.
Overall, they suggested that in order to inspire development of new vaccines that are safer, more effective and more protective, we will need to elicit both neutralizing antibodies and T cell responses.
Zhang, J., Ding, N., Ren, L. et al., 2021. COVID-19 Reinfection in the Presence of a Neutralizing Antibody. Clinical Medicine,.