The aim of this study was to identify and follow the long-term antibody response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (during first wave) in children and their household contacts.

This study included 6113 children (ages 0–18 years) who may have been exposed to ancestral SARS-CoV-2 in Germany from May 11 to June 30, 2020. Patients were recruited from inpatient and outpatient settings, as well as household contacts of SARS-CoV-2 positive study patients.

This was an observational prospective multicenter cohort study. Children with a positive SARS-CoV-2 PCR and/or antibody test, as well as their household contacts, were invited to 3 follow-up appointments with latest follow-up at 6 months. Nasopharyngeal swab was used for sequencing SARS-CoV-2 viral RNA, whereas venous sampling was used for antibody detection. Roche and DiaSorin antibody assays were used to detect SARS-CoV-2-specific antibodies in serum. Results were considered positive only if both assays yielded positive results.

In this study, 6113 children under 18 years of age were screened for SARS-CoV-2, with 4657 undergoing antibody testing. A total of 67 children (1.44% of all tested) were seropositive. The median time for presentation after infection was 83 days postsymptom onset (PSO). Most families had less than 100% seroprevalence, and those families with adult index cases had higher seroprevalence when compared with families with pediatric index cases (P = .047). In the follow-up phase, children had greater and more persistent antibody concentrations than the adults (ratio serum IgG spike in children versus adults 90 days PSO 1.75, P <  .001; 180 days PSO 1.38, P =  .01; 270 days PSO 1.54, P = .001). Children showed sustained seroconversion for up to 9 months PSO. At 6 months (>193 days after symptom onset), 97.6% of children remained nucleocapsid IgA, IgG, and IgM seropositive, whereas 100% of children remained spike IgG seropositive. Although spike IgG antibody levels were higher in children, their levels dropped more precipitously over time than in adults.

This study found that children had sustained long-term antibody response to SARS-CoV-2 (>6 months PSO) during the initial infection wave.

This was one of the first studies to look at ancestral SARS-CoV-2 seropositivity and compare antibody levels long-term between children and adults. Antispike IgG levels remained higher in children than adults over 193 days post symptom onset, even though a more rapid decline in serum antibody concentrations of children were observed initially. Most households did not have 100% seroprevalence, and those with pediatric index cases had lower seroprevalence. One limitation of this study is that it failed to evaluate the antibody levels in context with the participants’ clinical course of illness. The study highlights the dramatic and long-term antibody response children had to ancestral SARS-CoV-2, which is overall reassuring. Unfortunately, several more waves of SARS-CoV-2 have passed, and it hard to know how generalizable these data are to other SARS-CoV-2 variants. Although limited to the ancestral virus, this study offers an evidence-based foundation on long-term antibody response, which may be helpful as we suggest guidelines on when to vaccinate after SARS-CoV-2 infection.