Reduced seroconversion in children compared to adults with mild COVID-19

Abstract

Importance: The immune response in children with SARS-CoV-2 infection is not well understood. Objective: To compare seroconversion in children and adults with non-hospitalized (mild) SARS-CoV-2 infection and to understand the factors that influence this. Design: Participants were part of a household cohort study of SARS-CoV-2 infection. Weekly nasopharyngeal/throat swabs and blood samples were collected during the acute and convalescent period following PCR diagnosis for analysis. Setting: Participants were recruited at the Royal Childrens Hospital, Melbourne, Australia between May and October 2020. Participants: Those who had a SARS-CoV-2 PCR-positive nasal/throat swab. Main outcomes and measures: SARS-CoV-2 antibody and cellular responses in children and adults. Seroconversion was defined by seropositivity in all three serological assays. Results: Among 108 SARS-CoV-2 PCR-positive participants, 57 were children (median age: 4, IQR 2-10) and 51 were adults (median age: 37, IQR 34-45). Using three established serological assays, a lower proportion of children seroconverted compared with adults [20/54 69 (37.0%) vs 32/42 (76.2%); (p<0.001)]. This was not related to viral load, which was similar in children and adults [mean Ct 28.58 (SD: 6.83) vs 24.14 (SD: 8.47)]. Age and sex also did not influence seroconversion or the magnitude of antibody response within children or adults. Notably, in adults (but not children) symptomatic adults had three-fold higher antibody levels than asymptomatic adults (median 227.5 IU/mL, IQR 133.7-521.6 vs median 75.3 IU/mL, IQR 36.9-113.6). Evidence of cellular immunity was observed in adults who seroconverted but not in children who seroconverted. Conclusion and Relevance: In this non-hospitalized cohort with mild COVID-19, children were less likely to seroconvert than adults despite similar viral loads. This has implications for future protection following COVID-19 infection in children and for interpretation of serosurveys that involve children. Further research to understand why children are less likely to seroconvert and develop symptoms following SARS-CoV-2 infection, and comparison with vaccine responses may be of clinical and scientific importance.

Tracking the clonal dynamics of SARS-CoV-2-specific T cells in children and adults with mild/asymptomatic COVID-19

“…Several studies from Hong Kong, Australia and the United States have shown impaired humoral and cellular immune responses in children exposed to SARS-CoV-2 [ 10 , 26 , 76 , 105 ]. This agrees with our data showing impaired generation of T cell memory responses in children compared to adults.…”

The Challenge of Studying Long COVID: An Updated Review

“…Another unavoidable limitation includes the possibility that the uninfected control group is contaminated by children who have been infected with SARS-CoV-2 but who were not tested or who did not seroconvert. 40 Further, studies that evaluate a single time point might miss transitory or intermittent symptoms of long COVID. Finally, the range and the number of symptoms sought in studies vary considerably and some studies have been criticized for evaluating certain key symptoms.…”

Seroprevalence of SARS-CoV 2 antibodies & its determinants in children of 5-to-18-year age group in an urban setting, Kerala

“…This is in accordance with other studies, where children and adults with confirmed COVID positivity showed greater seropositivity. [ 10 20 ] The report of a recent survey conducted in our state also showed a seroconversion of more than 90% in children who had a history of COVID 19 positivity. [ 14 ] The delta variant, which was the predominant strain circulating in the community at the time of the study, may be the reason for the higher proportion of seroconversion.…”