Background Understanding pre-existing, cross-reactive immunity to SARS-CoV-2 is important for pan-coronavirus vaccine design. Since pre-existing T cell immunity has been associated with prior infection by circulating, endemic human coronaviruses (hCoVs), there has been recent interest in mapping hCoV exposure and immunity. However, few of these studies have been performed in Africa, where hCoV exposure may differ. We measured antibodies to endemic hCoVs in South African adults and adolescents, to gain insights into baseline exposure across different age groups.

Methods Using an established ELISA, we measured IgG specific for HKU1, 229E, OC43 and NL63 in pre-pandemic plasma from adolescents (n=14, ages 15–19) and adults (n=13, ages 20–50). A technical repeat was included for each sample, and samples were randomised within each assay plate. Data were analysed using non-parametric statistical tests.

Results In preliminary findings, antibodies specific for NL63, an alphacoronavirus, were detected in all adults and most adolescents (93%). Interestingly, fewer participants had antibodies to the other human alphacoronavirus, 229E, with IgG detected in 54% of adults and 50% of adolescents. Antibodies to the betacoronavirus, HKU-1, were present in all participants. We found no differences in the magnitude of responses between adults and adolescents for NL63, 229E and HKU-1, although a weak association with age was observed for NL63 (p=0.04, r=0.39) and HKU-1 (p=0.04, r=0.4). Finally, antibodies against OC43, another betacoronavirus, were measured in a subset (n=9) of adult participants, with responses detected in all.

Conclusion Our data suggest childhood exposure to endemic coronaviruses, such that adolescents already have detectable antibodies. Importantly, hCoV 229E may not circulate as frequently in South Africa compared to the global north, where reports confirm durable and detectable 229E antibody responses in adults. These geographical differences in exposure have important implications when considering the SARS-CoV-2 shift to endemicity, and the design of pan-coronavirus vaccines.