COVID-19 natural immunity

Key Messages:
• Within 4 weeks following infection, 90-99% of individuals infected with the SARS-CoV-2 virus develop detectable neutralizing antibodies.
• The strength and duration of the immune responses to SARS-CoV-2 are not completely understood and currently available data suggests that it varies by age and the severity of symptoms. Available scientific data suggests that in most people immune responses remain robust and protective against reinfection for at least 6-8 months after infection (the longest follow up with strong scientific evidence is currently approximately 8 months).
• Some variant SARS-CoV-2 viruses with key changes in the spike protein have a reduced susceptibility to neutralization by antibodies in the blood. While neutralizing antibodies mainly target the spike protein, cellular immunity elicited by natural infection also target other viral proteins, which tend to be more conserved across variants than the spike protein. The ability of emerging virus variants (variants of interest and variants of concern) to evade immune responses is under investigation by researchers around the world.
• There are many available serologic assays that measure the antibody response to SARS-CoV-2 infection, but at the present time, the correlates of protection are not well understood.

Current evidence points to most individuals developing strong protective immune responses following natural infection with SARSCoV-2. However, inaccurate immunodiagnostic tests may falsely indicate infected individuals as naïve to the virus (not previously infected) or may falsely label non-infected people as positive for immune markers of recent infection. To conclude, available tests and current knowledge do not tell us about the duration of immunity and protection against reinfection, but recent evidence suggests that natural infection may provide similar protection against symptomatic disease as vaccination, at least for the available follow up period.33 The emergence of variants of concern poses challenges and their potential to evade immunity elicited by either natural infection or by vaccination, needs to be closely monitored.

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