SARS-CoV-2 antibodies in kids after COVID may peak at 1 to 3 months

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In a group of nonhospitalized children 0 to 16 years old, SARS-CoV-2 neutralizing antibody levels peaked at about 84% 1 to 3 months after they tested positive for COVID-19 but remain high for more than a year, finds a single-center study published yesterday in JAMA Pediatrics.

The study involved pre-Omicron strains and also found that antibody response in the first month after infection was most durable in participants younger than 5 years.

From Feb 1, 2020, to Sep 30, 2021, researchers in Singapore analyzed SARS-CoV-2 neutralizing antibody responses in 126 children aged 0 to 16 years for up to 16 months after COVID-19 diagnosis. Average participant age was 7.4 years, 58.7% were boys, and 30% completed two to four visits for blood sampling.

Antibodies still 70% at 9 to 13 months

All patients with COVID-19 symptoms (72%) had a mild illness. The most common symptoms were fever, cough, and a runny nose. No patients developed multisystem inflammatory syndrome in children (MIS-C).

SARS-CoV-2 neutralizing antibody levels peaked at a median of 84% roughly 1 to 3 months after infection and remained at roughly 69.8% after 9 to 13 months. An adjusted analysis showed no association between neutralizing antibody levels by time since infection and patient characteristics such as sex and symptom status.

In the first month after infection, children younger than 5 years had the highest antibody levels (71.6%; 95% confidence interval [CI], 58.5% to 84.6%), while those aged 12 to 16 had the lowest (49.9%; 95% CI, 41.3% to 58.6%). Neutralizing antibody levels remained stable in the younger group at all time points for up to 16 months.

"The findings suggest that risk of SARS-CoV-2 reinfection in younger children is lower than in adults, which has important implications for scheduling COVID-19 vaccination after infection," the study authors wrote. "The findings also broaden the understanding about less severe clinical disease in younger children."

Findings subject to change amid Omicron

In a related editorial, Catherine Mary Healy, MD, of Baylor College of Medicine, said that the sample size was too small to draw definitive conclusions but that "it is somewhat reassuring that neutralizing antibodies persisted for a reasonable interval (9-13 months) following infection."

While there is no confirmed correlate of immunity nor a full understanding of the immune response to SARS-CoV-2, specifically on the role of cellular immunity, "it is hoped that this antibody persistence may at least protect against or ameliorate severe disease, even if it does not prevent subsequent infection," Healy wrote.

She also said that because the study period preceded dominance of the more transmissible yet milder-appearing Omicron variant, the findings are not likely to hold today. "Emerging data suggest that the new BA.2.12.1, BA.4, and BA.5 Omicron subvariants are capable of escaping neutralizing antibodies produced by prior infection with the Omicron BA.1 and BA.2 variants, thus explaining current surges in infection in communities with high rates of prior infection, vaccination, or both," she wrote.

SARS-CoV-2 will continue to evolve, Healy added: "With each change, the clinical expression of infection may change. To date, Omicron has resulted in relatively less severe disease than other variants (for example Delta) but that may not be the case in the future."

"In pediatrics, it is also encouraging that vaccines are available under emergency use authorization to children as young as 6 months of age, since, despite immune escape, vaccines remain protective against not only severe infection and death, but also potentially against MIS-C," she concluded.

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