Study: Young Children Previously Infected With COVID-19 May Have Long-term Immune Response

In prior research, investigators had observed that anti–SARS-CoV-2 spike protein receptor-binding domain (S-RBD) immunoglobulin G (Ig G) may persist for 18 months following infection in adults and children. However, investigators found during a recent study that children may have higher, and possibly longer, antibody peaks.¹

“This study suggests that the magnitude of SARS-CoV-2 S-RBD IgG antibodies is higher among younger children compared with older siblings and adults at all follow-up points,” wrote investigators in the study published in JAMA Network Open.¹

Additionally, investigators identified vaccination to be one of the most effective tools to quickly improve population herd immunity against SARS-CoV-2. Previous studies found that adults can have anti–S-RBD IgG for a year after infection, but investigators had remained uncertain regarding the duration of anti–SARS-CoV-2 antibodies in the pediatric population following infection.¹

Looking at the population with anti-S-RBD IgG is important to help investigators estimate the potential for long-term immunity against COVID-19.² For this reason, investigators decided to examine the kinetics of the anti–S-RBD IgG antibody in different family members to determine the immunity of different age groups.¹

To better understand pediatric immunity following a mild or asymptomatic infection of COVID-19, investigators conducted a single-center, prospective cohort study of 252 family clusters, which included 902 individuals in total, from April 1, 2020 to August 31, 2021. All participants attended the COVID-19 Family Cluster Follow-up Clinic at the Department of Women's and Children's Health at the University Hospital of Padua.¹

Among the participants, 351 were children or an older sibling who had a mean age of 8.6 years and 346 were parents. Additionally, a total of 697 individuals had a confirmed COVID-19 case, among whom 674 were mild or asymptomatic. Further, qualifying families included in the study had children younger than age 15 years and one family member who was infected with COVID-19.¹

After collecting titers of blood of the infected, investigators evaluated antibody levels at 1 to 4 months from baseline, 5 to 9 months, and at 10 or more months.¹

“Overall, higher levels of antibodies were observed among younger children compared with older children, adolescents, and adults, with an overall median S-RBD IgG titer in patients younger than 3 years 5-fold higher than adults,” investigators wrote in the study.¹

All age brackets experienced increased levels of anti-S-RBD IgG after infection, though the antibodies decayed over time and rapidly decreased within 200 days of infection. While different age groups had different antibody levels, specific cellular responses, genetics, the environment, and stochastic variables could impact long-term immune response, according to investigators.¹

“This study provided novel insights into the long-term features of the immune response to COVID-19 for different age classes, which could help in optimizing future COVID-19 vaccination strategies and prevention policies,” investigators wrote in the study.¹

The investigators noted that study limitations included follow-up times being either inconsistent or nonexistent due to pandemic restrictions. Additionally, investigators noted a limitation in identifying the baseline of infection among patients with a negative COVID-19 swab.¹

References

1. Costanza C, Cantarutti A, Costenaro P, et al. Long-term Immune Response to SARS-CoV-2 Infection Among Children and Adults After Mild Infection. JAMA Netw Open. 2022;5(7):e2221616. doi:10.1001/jamanetworkopen.2022.21616
2. Lo Sasso B, Agnello L, Giglio R, et al. Longitudinal analysis of anti-SARS-CoV-2 S-RBD IgG antibodies before and after the third dose of the BNT162b2 vaccine. Scientific reports. 12,8679(2022). doi:10.1038/s41598-022-12750-z