ABSTRACT
Background. Longitudinal serological surveillance is critical to understand dynamics of SARS-CoV-2 infections in children, a substantial portion of whom are asymptomatic. We describe trends in seroprevalence using at-home testing and evaluate demographic and clinical characteristics associated with seroconversion. Methods. Children 2-17 years old enrolled at 3 North Carolina sites (Figure 1) were followed April 2- December 31, 2021. Daily electronic surveys solicited symptoms and vaccination status. Four fingerprick lateral flow immunoassay tests were shipped to participants to be completed monthly;sensitivity and specificity were 84.5% and 99.0%, respectively. We defined an infection window as 30 days before a positive antibody test (IgG), excluding results after any vaccine. Asymptomatic was defined as absence of "new" symptoms in the window;"new" was defined as not occurring the 14 days preceding the first observation of the symptom in the window. Univariate logistic regression was used to compare participants with and without infection-induced antibodies. For estimated seroprevalence, we used Bayesian inference accounting for sensitivity and specificity, modeling IgG positives from a binomial distribution. Results. Of 1,501 participants, 9.1% developed infection-induced antibody (Table 1). Blacks were more likely to seroconvert (OR 1.95 [95% CI 1.05-3.45]) as were those in a 5-or-more person household (OR 4.25 [CI 1.47-12.1]). Cumulative seroprevalence of SARS-CoV-2 increased from 12.7% in May to 32.4% in October (Figure 2);61% of those seropositive were asymptomatic (Table 2). Adolescents had the highest seroconversion rates and were significantly more likely than 2-4-year olds to be asymptomatic. Conclusion. Prior SARS-CoV-2 seroprevalence data in children are limited by cross sectional design and use of convenience samples. With serial testing, we demonstrate rising SARS-CoV-2 seroprevalence, with highest rates of seroconversion in adolescents. Although prior findings suggest that asymptomatic infections occur most frequently in young children, we found a high proportion among adolescents. Our findings underscore the importance of serosurveillance to optimize public health efforts aimed at children and adolescents. (Table Presented).
ABSTRACT
Background. Well-regulated clinical trials have shown authorized COVID-19 vaccines to be immunogenic and highly efficacious. Information about antibody responses after vaccination in real-world settings is needed. Methods. We evaluated seroconversion rates in adults reporting ≥ 1 dose of an authorized COVID-19 vaccine in a U.S. multistate longitudinal cohort study, the COVID-19 Community Research Partnership. Participants were recruited through 12 participating healthcare systems and community outreach. Participants had periodic home-based serologic testing using either a SARSCoV-2 nucleocapsid and spike IgM/IgG lateral flow assay (63% of participants) or a SARS-CoV-2 spike IgG enzyme-linked immunosorbent assay (37% of participants). The timing and number of tests before and after vaccination varied based on participant time in study. Participants were included if they were seronegative on the last test before and had >1 test result after vaccination (some had previously been seropositive, but seroreverted). A weighted Cox regression model with right censoring was used to obtain adjusted hazard ratios for sex, age, race/ethnicity, and prior seropositivity. Time-to-event (seroconversion) was defined as time to first positive test > 4 days after vaccination;participants were censored at the date of their last available test result. Results. 13,459 participants were included and 11,722 seroconverted (Table). Median time in study was 272 days (range 31-395). Median follow-up time from vaccine to last available test was 56 days (range 1-147). Participants had a median of 3 tests (range 1-12) before and 2 tests (range 1-8) after vaccination. Based on the Kaplan-Meier method, median time to seroconversion after first COVID-19 vaccination was 35 days (interquartile range: 25-45). Likelihood of seroconversion decreased with older age (Table). Female participants, non-Hispanic Black participants, and participants who were previously seropositive were more likely to seroconvert (Table). Conclusion. All subgroups had high rates of seroconversion, with some small differences in likelihood of seroconversion between subgroups. These data demonstrate the excellent immunogenicity of COVID-19 vaccines in real-world settings in the US.