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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.

Objectives: Although medications for opioid use disorder (MOUD) save lives, treatment retention remains challenging. Identification of interventions to improve MOUD retention is of interest to policymakers and researchers. On behalf of the Agency for Healthcare Research and Quality, we conducted a rapid evidence review on interventions to improve MOUD retention. Methods: We searched MEDLINE and the Cochrane Library from February 2009 through August 2019 for systematic reviews and randomized trials of care settings, services, logistical support, contingency management, health information technology (IT), extended-release (XR) formulations, and psychosocial interventions that assessed retention at least 3 months. Results: Two systematic reviews and 39 primary studies were included; most did not focus on retention as the primary outcome. Initiating MOUD in soon-to-be-released incarcerated people improved retention following release. Contingency management may improve retention using antagonist but not agonist MOUD. Retention with interventions integrating medical, psychiatric, social services, or IT did not differ from in-person treatment-as-usual approaches. Retention was comparable with XR- compared to daily buprenorphine formulations and conflicting with XR-naltrexone monthly injection compared to daily buprenorphine. Most psychosocial interventions did not improve retention. Discussion: Consistent but sparse evidence supports criminal justice prerelease MOUD initiation, and contingency management interventions for antagonist MOUD. Integrating MOUD with medical, psychiatric, social services, delivering through IT, or administering via XR-MOUD formulations did not worsen retention. Fewer than half of the studies we identified focused on retention as a primary outcome. Studies used different measures of retention, making it difficult to compare effectiveness. Additional inquiry into the causes of low retention would inform future interventions. Registration: PROSPERO: CRD42019134739

Aims. American deaths from opioid overdose now approach 50,000 annually. While evidence shows that medications for addiction treatment (MAT) save lives, retaining patients in MAT programs is challenging. The U.S. Agency for Healthcare Research and Quality, on behalf of the U.S. Department of Health and Human Services, commissioned a rapid evidence review on the effectiveness of interventions to promote a broader understanding of the published literature on MAT retention among adults with opioid use disorder (OUD). Methods. We searched MEDLINE and the Cochrane Library from February 12, 2009, through August 20, 2019, for systematic reviews (SRs) and randomized controlled trials (RCTs). We summarized evidence for six retention intervention types: care settings/services/logistical support, contingency management, health information technology (IT), extended-release (XR) medication-based treatment, psychosocial support, and financial support. Our primary outcome was retention, defined as continued medication engagement for at least 3 months after MAT initiation. Secondary outcomes included mortality and harms. Findings. Key findings from 2 SRs and 39 primary studies include: • Most studies of MAT for OUD do not focus on retention as the primary outcome, are small (e.g., one to two trials per intervention), and have design flaws. • Care setting interventions that initiated MAT in soon-to-be-released incarcerated patients improved retention following release. • Contingency management improved retention when combined with antagonist MAT, but not with agonist forms of MAT. Applicability, however, may be limited due to implementation challenges. • Preliminary trials suggest that retention in MAT supported with health IT approaches may be no worse than in-person approaches. • Early studies suggest no difference in retention with XR-buprenorphine in either injectable or implant formulations compared with daily buprenorphine. There were conflicting results with XR-naltrexone injection compared with daily buprenorphine. • The addition of psychosocial interventions did not improve retention; however, many studies included some form of counseling in the control groups, potentially obscuring evidence of effectiveness. Harms were infrequently reported across studies except in studies of XR formulations. Similarly, few studies reported whether participant characteristics influenced retention. Conclusions. While patients who receive longer-term treatment with MAT have improved outcomes, fewer than half of the identified studies measured treatment retention as a primary outcome. Limited evidence suggests criminal justice prerelease MAT initiation and the use of contingency management for patients on antagonist forms of MAT may aid retention. XR viii and daily buprenorphine formulations appear to be equivalent for treatment retention and comparisons of XR-naltrexone versus daily buprenorphine showed conflicting results. Integrating MAT treatment with medical and social services and the use of health IT did not change retention. Some s...

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

 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.

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