SARS-CoV-2 seroprevalence and determinants of infection in young adults: a population-based seroepidemiological study

OBJECTIVES: Most SARS-CoV-2 seroprevalence studies have focussed on adults and high-risk populations, and little is known about young adults. The objective of the present study was to provide evidence on the SARS-CoV-2 seroprevalence among young adults in Germany and to explore determinants associated with seropositivity in general and, specifically, with previously undetected infections. STUDY DESIGN: This was a population-based SARS-CoV-2 seroprevalence study. METHODS: In November 2020, a population-based study on SARS-CoV-2 seroprevalence in young adults (aged 18–30 years) was conducted in a large German city. Serum samples were obtained to analyse the SARS-CoV-2 antibody status using the Elecsys Anti-SARS-CoV-2 immunoassay. Descriptive statistics and odds ratios (ORs) of seropositivity and of previously undetected infections in relation to different determinants were calculated. RESULTS: Among 2186 participants, SARS-CoV-2 antibodies were detected in 72 individuals, equalling a test performance-adjusted seroprevalence of 3.1% (95% confidence interval [CI]: 2.4–4.0). Based on reported COVID-19 cases to the public health authority, a moderate underascertainment rate of 1.7 was calculated. Seropositivity was higher among individuals who sought COVID-19-related information from social media (OR: 1.83, 95% CI: 1.2–3.1), and undetected COVID-19 infections were more prevalent among men and those not adhering to social distancing. CONCLUSIONS: The results show a substantial underascertainment of SARS-CoV-2 infections among young adults and indicate that seroprevalence is likely to be much higher than the reported COVID-19 prevalence based on confirmed COVID-19 cases in Germany. Preventive efforts should consider the heterogeneity of risk profiles among the young adult population.