Mild SARS-CoV-2 Infections and Neutralizing Antibody Titers

PURPOSE OF THE STUDY: To examine the production and persistence of neutralizing antibodies against SARS-CoV-2 in a cohort of family clusters with history of coronavirus disease 2019 (COVID-19). STUDY POPULATION: The study enrolled 57 Italian families over a 6-month period (March 1–September 4, 2020) who met the inclusion criteria, which required that the families had a child or children of pediatric age (<15 years old) and had at least 1 immediate family member with a history of COVID-19. METHODS: Families were enrolled 4 to 8 weeks after the end of isolation or hospitalization. They underwent clinical evaluation, and blood samples were collected from confirmed COVID-19 cases. Confirmed cases were defined as having a history of positive polymerase chain reaction (PCR) testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) or having a positive serologic test (chemiluminescence immunoassay or plaque reduction neutralizing test). Data regarding the date of infection, severity of illness, and age at the time of illness were retrospectively collected. RESULTS: During this study, 57 family clusters were evaluated. Of these, 209 recruited subjects underwent serological assessment. In total, 152 confirmed COVID-19 cases were identified, with 70 children or older siblings and 82 parents making up these confirmed cases. The median age for the group of children and older siblings was 8 years old, and the median age for the parent cohort was 42 years old. Neutralizing antibodies persisted up to 7 to 8 months from infection with only a modest decline over time. Neutralizing antibodies inversely correlated with age with children <6 years old (particularly toddlers <3 years old) showing the highest levels. Mildly affected children (<6 years old) showed increasing levels of neutralizing antibodies over the study time (236 days from time of infection). CONCLUSIONS: This study provides a longitudinal evaluation of neutralizing antibody production and duration in asymptomatic and mildly symptomatic patients from familial clusters. Of the participants in this study, younger children developed higher levels of neutralizing antibody compared with older siblings or adults.