Key Questions1. What is the prevalence, level, and durability of detectable anti-SARS-CoV-2 antibodies among adults infected with or recovered from reverse transcription polymerase chain reaction (RT-PCR) -diagnosed SARS-CoV-2 infection? a. Do the levels and durability of detectable antibodies vary by patient characteristics (e.g., age, sex, race/ethnicity, and comorbidities), COVID-19 severity, presence of symptoms, time from symptom onset, or as measured by different types of immunoassays (e.g., immunoassay sensitivity/specificity)? 2. Do anti-SARS-CoV-2 antibodies confer natural immunity against reinfection? a. Does conferred immunity vary by factors such as initial antibody levels, patient characteristics, presence of symptoms, or severity of disease? b. Is there a threshold level of detectable anti-SARS-CoV-2 antibodies necessary to confer natural immunity, and if so, does this threshold vary by patient characteristics (e.g., age, sex, race/ethnicity, and comorbidities)? 3. If anti-SARS-CoV-2 antibodies confer natural immunity against reinfection, how long does this immunity last? a. Does immunity vary by factors such as initial antibody levels, patient characteristics, presence of symptoms, or severity of disease? 4. What are the unintended consequences of antibody testing after SARS-CoV-2 infection? Key Question 1: Prevalence, Levels, and Duration of Detectable Antibodies in SARS-CoV-2 Infection Summary prevalence estimates are presented in Table 1, and an overview of how antibody levels trend over time is presented in Table 2. Detailed prevalence results from seroprevalence, cross-sectional, and cohort studies are presented in Appendix Table C-3 and prevalence results from immunoassay validation studies are presented in Appendix Table C-4. Strength of evidence assessments are summarized in Appendix E. Table 1. IgM, IgG, IgA and neutralizing antibody prevalence Antibody Subtype Peak Prevalence Estimate (%) Number of Studies; Total Number (N) of RT-PCR+ Participants IgM Median 80* (Range: 9-98) when measured approximately 20 days post-symptom onset or RT-PCR diagnosis