Serum IgG and mucosal IgA antibodies from pre-pandemic samples collected in Kilifi, Kenya, neutralize SARS-CoV-2 in vitro.
Nyagwange J., Kutima B., Mwai K., Karanja HK., Gitonga JN., Mugo D., Sein Y., Wright D., Omuoyo DO., Nyiro JU., Tuju J., Nokes DJ., Agweyu A., Bejon P., Ochola-Oyier LI., Scott JAG., Lambe T., Nduati E., Agoti C., Warimwe GM.
OBJECTIVES: Many regions of Africa have experienced lower COVID-19 morbidity and mortality compared to Europe. Pre-existing humoral responses to endemic human coronaviruses (HCoV) may cross-protect against SARS-CoV-2. We investigated neutralizing capacity of SARS-CoV-2 spike reactive and non-reactive IgG and IgA antibodies in pre-pandemic samples. METHODS: To investigate the presence of pre-existing immunity, we performed ELISA using spike antigens from reference SARS-CoV-2, HCoV HKU1, OC43, NL63 and 229E using pre-pandemic samples from Kilifi in coastal Kenya. Additionally, we performed neutralization assays using pseudotyped reference SARS-CoV-2 to determine functionality of the identified reactive antibodies. RESULTS: We demonstrate presence of HCoV serum IgG and mucosal IgA antibodies which cross-react with the SARS-CoV-2 spike. We show pseudotyped reference SARS-CoV-2 neutralization by pre-pandemic serum with a mean ID50 of 1:251, which is ten-fold less than that of pooled convalescent sera from COVID-19 patients but still within predicted protection levels. The pre-pandemic naso-oropharyngeal fluid neutralized pseudo-SARS-CoV-2 at a mean ID50 of 1:5.9 in the neutralization assay. CONCLUSION: Our data provide evidence for pre-existing functional humoral responses to SARS-CoV-2 in Kilifi, coastal Kenya and adds to data showing pre-existing immunity for COVID-19 from other regions.