At last a study published in bioRxiv by Dan and others as a preprint looks at this important topic.

Understanding immune memory to SARS-CoV-2 is critical for improving diagnostics and vaccines and assessing the likely future course of the pandemic.

The author’s analysed multiple compartments of circulating immune memory to SARS-CoV-2 in 185 COVID-19 cases, including 41 cases greater than equal to six months post-infection.

  • Spike IgG was relatively stable over the six plus months.
  • Spike specific memory B cells were more abundant at six months than at one month.
  • SARS-CoV-2 specific CD4 plus T cells and CD8 plus T cells declined with a half limit of three to five months.

When considering potential connections between immune memory and protective immunity, it is key to consider the available epidemiological data.

Individual case reports demonstrate that re-infections with SARS-CoV-2 are occurring.

What is currently lacking is an epidemiological framework for quantifying how rare or common such re-infection events are.

Thus, interpretations of current events are very constrained.

There is a high degree of heterogeneity in the magnitude of adaptive immune responses to SARS-CoV-2. This heterogeneity was observed in their study to be carried out on the immune memory phase to SARS-CoV-2.

It may be expected that at least a fraction of the SARS-CoV-2 infected population with particularly low immune memory might be susceptible to re-infection relatively quickly.
This requires further investigations and may result from a low cumulative viral load of the initial infection.

This results in a minor or transient infection that barely triggers an adaptive immune response in some individuals.

Nevertheless, immune memory consisting of at least three immunological compartments were measurable in 90% of subjects in this study at greater than or equal to five months post-infection.

This therefore indicates that durable immunity against SARS-CoV-2 and COVID-19 disease is possible in most individuals.

Dr Paul Ettlinger
London General Practice

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