In just over year since SARS-CoV-2 emerged, new vaccines approved for emergency use have been developed and are currently being rolled out. Vaccination aims to induce long-lived immunity, however, a very important question is: how long does naturally induced SARS-CoV-2 immunity last? Multiple studies have demonstrated a significant decline in circulating SARS-CoV-2 specific antibodies as early as a month post-recovery, however, this only represents one aspect of adaptive immunity. Two recently published studies provide evidence for longer (-lived) SARS-CoV-2 immunity.
Hartley et al. aimed to determine the longevity and immunophenotype of SARS-CoV-2-specific memory B cells in COVID-19 patients. The immunophenotyped 36 samples (11 of which were paired) from individuals between 4 and 242 days post-COVID-19 symptom onset. They demonstrated that though serum levels of SARS-CoV-2-specific Abs decline and reach a plateau, SARS-CoV-2-specific memory B cells that express IgG1 (and IgM) persist long-term and continue to increase during convalescence. Based on their findings they propose “that vaccination studies could potentially use SARS-CoV-2 memory B cells as a surrogate marker of robust humoral immunity as circulating antibodies are known to wane rapidly following antigen clearance”.
Dan et al., performed a comprehensive analysis of multiple compartments of adaptive immunity: antibodies, B cells, CD8+ T cells, and CD4+ T cells using samples from 188 recovered COVID-19 patients. This large cohort included approximately 15% of samples taken more than 6-months post-infection. They also observed a significant increase in circulating memory B cells during convalescence. However, SARS-CoV-2-specific CD4+ T cells and CD8+ T cells declined with a half-life of 3-5 months. They conclude that despite observing subset specific differences in the durability of SARS-CoV-2 immunity, their data:
“show immune memory in at least three immunological compartments was measurable in ~95% of subjects 5 to 8 months post-symptom onset, indicating that durable immunity against secondary COVID-19 disease is a possibility in most individuals.”
In summary, both studies provide hope for long-lasting memory B cell immunity which persists despite a decline in circulating SARS-CoV-2-antibodies. Further, they highlight specific immune compartment that could be used as better markers of persisting immunity in vaccination studies.
- Hartley et al., 2020. Rapid generation of durable B cell memory to SARS-CoV-2 spike and nucleocapsid proteins in COVID-19 and convalescence. Science
- Dan et al., 2020. Immunological memory to SARS-CoV-2 assessed for up to 8 months after infection. Science
Summary by Cheleka AM Mpande