Longitudinal Follow-up of Antibody Responses in Pediatric Patients With COVID-19 up to 9 Months After Infection

Pediatr Infect Dis J. 2021 Aug 1;40(8):e294-e299. doi: 10.1097/INF.0000000000003199.


Introduction: Antibody response developed within 2-3 weeks after exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been shown to decrease over time; however, there is limited data about antibody levels at 6 months or later postinfection, particularly in children.

Materials and method: A prospective multicenter study was performed using 315 samples of 74 confirmed and 10 probable coronavirus disease 2019 pediatric cases. About 20% of these cases were classified as asymptomatic, 74% as mild/moderate and 6% as severe/critical. Patients were included if at least 2 samples were available. The antibody response was classified as either early-period or late-period (14 days-3 months and after 6 months, respectively) for IgG response whereas IgA response was tested on various time intervals, including as early as 4 days up to 3 months. Euroimmun Anti-SARS-CoV-2 IgG and IgA and Genscript SARS-CoV-2 Surrogate Virus Neutralization Kits were used for antibody detection.

Results: There was no difference between the early-period and late-period IgG positivity (P = 0.1). However, the median IgG levels were 11.98 in the early periods and 4.05 in the late periods, with a significance of P < 0.001. Although the decrease in IgG levels was significant in asymptomatic and mild/moderate cases (P < 0.008 and P < 0.001, respectively), the decrease in severe/critical cases was moderate (P = 0.285). The sensitivity of the IgG after 15 days was higher than 94%, and the sensitivity of IgA was 88% on days 8-15.

Conclusion: SARS-CoV-2 IgG antibody levels decreased after 6 months. The decrease was moderate in severe/critical cases. Overall, 95.8% of the patients remained positive up to 9 months after infection. Although the IgA response may be useful early on, the IgG response is useful after 14 days.

MeSH terms

  • Adolescent
  • Antibodies, Viral / biosynthesis*
  • Antibodies, Viral / immunology
  • Antibody Formation
  • COVID-19 / immunology*
  • Child
  • Child, Preschool
  • Female
  • Follow-Up Studies
  • Humans
  • Immunoglobulin A
  • Immunoglobulin G / biosynthesis
  • Immunoglobulin G / immunology
  • Infant
  • Longitudinal Studies
  • Male
  • Prospective Studies
  • SARS-CoV-2 / immunology*


  • Antibodies, Viral
  • Immunoglobulin A
  • Immunoglobulin G