Longitudinal study of severe acute respiratory syndrome coronavirus (SARS-CoV-2) antibody titers in children exposed to SARS-CoV-2 infection

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection induces an early immunoglobulin (Ig)M response followed by IgG antibodies, which confer protection against reinfection. Data on the prevalence and persistence of SARS-CoV-2 antibodies in children are limited. Aims and Objective: The aim of the study was to evaluate SARS-CoV-2 seropositivity and antibody persistence in children with previous COVID-19 infection or household exposure. Materials and Methods: This prospective cross-sectional follow-up study was conducted in a tertiary teaching hospital. Children aged 1 year–<18 years with reverse transcription polymerase chain reaction (RT-PCR)–confirmed COVID-19 or documented household exposure to an RT-PCR–positive family member at least 6–8 weeks before enrolment were included after informed consent. Venous blood samples were obtained at enrolment and again at 5 (±2) months. Enzyme-linked immunosorbent assay was used to assess total SARS-CoV-2 antibodies (IgM, IgG, IgA). Seropositivity was defined as antibody titers >11 AU/mL. Results: Out of 100 children enrolled; 54% were male, and 52% resided in rural areas. About 46% of children had confirmed COVID-19 infection. At enrolment, 75% of children were seropositive, with a mean antibody titer of 40.33±19.84 AU/mL. At 5-month follow-up, 86.7% (65/75) of initially seropositive children remained seropositive, while 13.3% (10/75) lost seropositivity, with a significant mean decline in titers of 12.34±15.20 AU/mL (P<0.001). Antibody levels showed no significant association with age, sex, nutritional status, or mode of exposure. Conclusion: Most children develop seroconversion for SARS-CoV-2 after infection, with persistence of seropositivity for at least 5 months in the majority. These findings improve understanding of antibody-mediated immunity to SARS-CoV-2 in children.