Study suggests children develop short-term humoral immunity following SARS-CoV-2 infection

A single-center, cross-sectional epidemiological survey conducted in Israel has recently pointed out that antibodies induced by natural severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in children start declining just after 4 months of acute infection. However, their seropositivity rates are not impacted by school reopening. The study has recently been published in the journal Acta Paediatrica.

Background

Since its emergence in December 2019, SARS-CoV-2, the causative pathogen of coronavirus disease 2019 (COVID-19), has infected 188 million people and claimed 4 million lives globally. In children, the virus has mostly caused mild infection, with significantly lower morbidity and mortality than adults and older adults. However, the virus has been found to cause multisystem inflammatory syndrome (MIS) in a small subset of children weeks after infection onset. Primarily, MIS affects school children and causes serious complications in multiple organs due to excessive inflammation.

Studies investigating robustness and durability of humoral immunity have indicated that anti-SARS-CoV-2 antibodies remain active even after 10 months of infection onset in adults. Similarly, vaccine-induced immunity has shown equivalent durability in adults. However, not enough information is available regarding the long-term immune response against SARS-CoV-2 in children.

In the current study, the scientists have investigated the prevalence of SARS-CoV-2 infection in children by conducting IgG-specific anti-SARS-CoV-2 antibody testing. In children with a known history of infection, they have determined the durability of antibody response. Moreover, they have investigated whether school reopening has influenced the infection rate in children and adolescents under the age of 18 years.

Study design

The study was conducted on 1,138 patients under 18 years (age range: 1.3 – 11.3 years) who visited the pediatric emergency department of a medical center in Jerusalem, Israel, between October 2020 and January 2021. The details about demographic background, medical history, possible SARS-CoV-2 exposure, and history of PCR-confirmed COVID-19 and symptoms were collected from all patients.

The blood samples collected from the patients were analyzed for IgG-specific anti-nucleocapsid and anti-spike antibodies.  

Important observations

Of all enrolled patients, only 10% were seropositive, meaning that they had detectable anti-SARS-CoV-2 antibody levels in the blood. Of all seropositive patients, only 44% had a history of PCR-confirmed SARS-CoV-2 infection. Importantly, among patients with family members who tested positive for SARS-CoV-2, only 31% exhibited detectable antibody levels.

A significant positive correlation was observed between seropositivity and older age, being Muslim or orthodox Jewish, and having a large family size. Moreover, an age-dependent induction in seropositivity rate was observed. Specifically, seropositivity was observed in about 6% of patients under the age of 1 and 14% of adolescents aged 12 – 18 years.  

Overall, only 6% of all patients mentioned having a history of confirmed SARS-CoV-2 infection. Of them, 70% were seropositive. The seronegative status was more frequent in patients who remained asymptomatic during the active infection period. In contrast, patients with SARS-CoV-2 related multisystem inflammatory syndrome had higher antibody titers than other seropositive patients.

Regarding the durability of antibody response, significantly higher antibody titers were observed in blood samples taken within 22 – 119 days of the active infection. The titers dropped significantly after 4 months in all seropositive patients with known SARS-CoV-2 infection. A variation in antibody response was also observed by age, with patients under the age of 6 years having higher antibody levels than older patients. However, after 60 days of infection, the antibody levels declined sharply in younger patients.

During the 90-day study period, no variation in weekly seropositivity rates was observed, despite school reopening. Moreover, no significant difference in infection rate was observed between children who attended or were absent from school during the lockdown.

Study significance

The study reveals that about 41% of children with detectable anti-SARS-CoV-2 antibody levels do not have a known history of PCR-confirmed infection or suspected viral exposure. However, the durability of humoral immunity is relatively short-term in children than adults, with antibody levels declining sharply after 4 months of acute infection. Important, the study highlights that school reopening does not increase the rate of infection in children.

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