Antibody tests for SARS-CoV-2, the virus that causes COVID-19, are widely available. This living review summarizes the evidence on the prevalence, levels, and durability of detectable antibodies after SARS-CoV-2 infection and whether antibodies to SARS-CoV-2 confer protective immunity. The review will be updated as more evidence becomes available.

Patients and clinicians want to know who is protected from SARS-CoV-2 infection. This update is part of a living systematic review to understand the potential value of antibody testing as a correlate of protection against infection. Because the previous review found that seroconversion was a near-universal consequence of recent infection in immunocompetent patients, this review examines the risk for reinfection in adults after SARS-CoV-2 infection, whether diagnosed by polymerase chain reaction test, antibody test, or a combination of both.

 Evidence suggests that the majority of adults develop detectable levels of immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies following infection with SARS-CoV-2 (moderate strength of evidence* [SoE]).  IgM levels peak approximately 20 days after symptom onset or RT-PCR diagnosis and subsequently decline. IgG levels peak approximately 25 days after symptom onset or RT-PCR diagnosis and may remain detectable for at least 120 days (moderate SoE*).  Almost all adults develop neutralizing antibodies in response to SARS-CoV-2 infection, and these antibodies may remain detectable for at least 152 days (low SoE*).  A small percentage of people do not develop antibodies in response to SARS-CoV-2 infection for reasons that are largely unclear but may be related to less severe disease or absence of symptoms.  Antibody prevalence does not appear to vary by age or sex, but older age may be associated with higher antibody levels (low SoE*). Non-White race may be associated with higher antibody prevalence and levels (low SoE*). COVID-19 severity and presence of symptoms may also be associated with higher antibody prevalence or levels (low SoE*). More evidence is needed to draw stronger conclusions regarding how the antibody response varies by patient characteristics and disease factors.  Studies to date have not established the relationship between the development of antibodies after RT-PCR-diagnosed SARS-CoV-2 infection and the risk of reinfection. Studies based on index serologic testing suggest that the presence of antibodies is associated with a lower risk of a subsequent positive SARS-CoV-2 RT-PCR test.