Antibody responses to SARS COV-2 is usually detected in the patients’ blood within 8-14 days following the onset of COVID-19 symptoms. However, due to the recent emergence of this virus in the human population it is not yet known how long these Ab responses will be maintained or whether they will provide protection from re-infection. Antibody responses to other human coronaviruses have been reported to wane over time. In particular, Aantibody responses targeting endemic human alpha and betacoronaviruses can last for as little as 12 weeks, whereas Abs to SARS-CoV and MERS can be detected in some individuals 12-34 months after infection. It is important to understand the immune responses following infection to define parameters in which Aantibody tests can provide meaningful data. Although several cross-sectional studies of antibody responses arising from SARS-CoV-2 infection have been reported, there is currently limited information on the longevity of the antibody response.

 Aims

To understand the kinetics of antibody development and try to understand the durability of the antibody response.

To understand the nature of antibody expressed in asymptomatic individuals

Study design: It will be a prospective observational study on HCWs who were tested positive for SARS COV2 infections by RT PCR

Study population & Inclusion Criteria: At least 45 HCWs with positive RT PCR for COVID will be included in the study.

 Exclusion Criteria:

Samples that do not have sufficient volume to complete testing on the VITROS^® Immunodiagnostics system (i.e. less than 1.0 mL)

Grossly haemolysed, icteric or turbid samples, or samples with visible particulates that are not getting removed even after centrifugation.

Samples which have been subjected to more than two freeze thaw cycles.

Samples from patients for whom the time between symptom onset and collection of samples cannot be determined.

 Materials & Methods

Two sequential samples from HCWs in the convalescent phase will be taken for subjects enrolled in the study. Samples will be collected in a gap of one month. Subjects who come negative for antibodies earlier will not be followed up further.

Informed consent will be taken from all subjects before enrolling into the study. Each subject will have to sign a declaration form and fill up a questionnaire for exposure history, type of symptoms and risk factors. Disease will be categorized into mild, moderate and severe based on severity symptoms and requirement of oxygen or ventilator as per clinical management guidelines by MoHFW, Govt. of India.

Clinical samples: 3 ml of serum sample will be collected from all subjects enrolled in the study who were positive for SARS COV-2 RT-PCR. For all the patient samples, the information viz., Date of Symptoms first observed, date of sample collection, the date of RTPCR showing positive shall also be recorded. 

Detection of Antibody levels

The test will be done in-house using a kit approved by ICMR for surveillance. The VITROS Immunodiagnostic Anti-SARS-CoV-2 IgG which is a chemiluminescence based assay, will be used for detection of IgG. The sensitivity for samples collected >15 days of onset of symptoms is 90% and the clinical specificity is 100% as mentioned in the kit literature.

We will also measure the neutralizing antibody levels of all the subjects by using the the LIAISON® SARS-CoV-2 S1/S2 IgG test. The LIAISON® SARS-CoV-2 S1/S2 IgG uses chemiluminescence immunoassay (CLIA) technology for the Quantitative determination of anti-S1 and anti-S2 specific IgG antibodies to SARS-CoV-2 in human serum or plasma samples.