Nayak 2021.

Study characteristics
Patient Sampling	Purpose: Diagnosis of convalescent‐phase infection Design: Two‐group study to estimate sensitivity and specificity [1] Confirmed COVID‐19 patients, RT‐PCR +ve, n = 42 [2] Pre‐pandemic controls n = 22 Group [2] not eligible for our review as < 25 samples Recruitment: COVID‐19‐recovered individuals recruited from Shaheed Hasan Khan Mewati Government Medical College, Haryana, India, Super Specialty Pediatric Hospital and Post Graduate Teaching Institute, Noida and ICMR‐National Institute of Malaria Research, New Delhi Prospective or retrospective: [1] Unclear [2] Retrospective Sample size: 64 (42) of which 42 (42) were eligible for our review Further detail: [1] SARS‐CoV‐2 PCR‐positive at the time of initial diagnosis, and PCR‐negative when recruited for this study [2] Not stated Exclusions not reported
Patient characteristics and setting	Setting: Convalescent Location: Shaheed Hasan Khan Mewati Government Medical College, Haryana, India, Super Specialty Pediatric Hospital and Post Graduate Teaching Institute, Noida and ICMR‐National Institute of Malaria Research, New Delhi Country: India Dates: Not stated, 25‐84 days post‐PCR +ve Symptoms and severity: Not stated, all recovered Demographics: Mean age 39.4 years (range 15‐70); 38 males, 4 females Exposure history: Not stated Non‐Covid group 1: NA
Index tests	Test name: COVID‐Kavach ELISA test kit Manufacturer: Zydus diagnostics, Calida Healthcare Limited Antibody: IgG Antigen target: Not stated Evaluation setting: Laboratory Test method: ELISA Timing of samples: 25‐84 days post‐PCR +ve Samples used: Plasma Test operator: Not stated, laboratory staff? Definition of test positivity: >= 1.5 Blinding reported: Unclear Threshold predefined: Unclear, performed as per manufacturer instructions
Target condition and reference standard(s)	Reference standard: RT‐PCR assay as the standard operating procedures established by Indian Council of Medical Research (ICMR)‐National Institute of Virology (NIV), Pune, India under the Government of India guidelines for COVID19 diagnosis (ICMR‐NIV, 2020) Threshold not stated Samples used: Nasopharyngeal and throat swabs Timing of reference standard: Not stated Blinded to index test: Yes Incorporated index test: No Definition of non‐COVID cases: NA Samples used: NA Timing of reference standard: NA Blinded to index test: NA Incorporated index test: NA
Flow and timing	Time interval between index and reference tests: 25‐84 days All patients received same reference standard: yes Missing data: Not stated Uninterpretable results: Not stated Indeterminate results: Not stated Unit of analysis: Patients
Comparative
Notes	Funding: Supported in part by Indian Council of Medical Research VIR/COVID‐19/02/2020/ECD‐1. Individual authors supported through Dengue Translational Research Consortia National BioPharma Mission, DBT grant, DBT/Wellcome Trust India Alliance Early Career Fellowship grant Publication status: Published paper Source: Virology Author COI: Authors declared no known competing financial interests or personal relationships.
Methodological quality
Item	Authors' judgement	Risk of bias	Applicability concerns
DOMAIN 1: Patient Selection
Was a consecutive or random sample of patients enrolled?	Unclear
Was a case‐control design avoided?	No
Did the study avoid inappropriate exclusions?	Unclear
Did the study avoid inappropriate inclusions?	Unclear
Could the selection of patients have introduced bias?		High risk
Are there concerns that the included patients and setting do not match the review question?			High
DOMAIN 2: Index Test (All tests)
DOMAIN 2: Index Test (Antibody tests)
Were the index test results interpreted without knowledge of the results of the reference standard?	Unclear
If a threshold was used, was it pre‐specified?	Yes
Could the conduct or interpretation of the index test have introduced bias?		Unclear risk
Are there concerns that the index test, its conduct, or interpretation differ from the review question?			Low concern
DOMAIN 3: Reference Standard
Is the reference standards likely to correctly classify the target condition?	Yes
Were the reference standard results interpreted without knowledge of the results of the index tests?	Yes
The reference standard does not incorporate the index test	Yes
Could the reference standard, its conduct, or its interpretation have introduced bias?		Low risk
Are there concerns that the target condition as defined by the reference standard does not match the question?			High
DOMAIN 4: Flow and Timing
Was there an appropriate interval between index test and reference standard?	Unclear
Did all patients receive the same reference standard?	Yes
Were all patients included in the analysis?	Yes
Did all participants receive a reference standard?	Unclear
Were results presented per patient?	Yes
Could the patient flow have introduced bias?		Unclear risk