Examining the association of live virus neutralisation activity of capillary microsamples and risk of SARS-CoV-2 infections: a nested case control study within the Virus Watch community cohort

Due to the proliferation of new SARS-CoV-2 variants, most COVID-19 cases are now caused by post-vaccine infections and a substantial proportion are reinfections. While prior research on correlates of protection has focused on the role of anti-spike antibodies, the results of the corresponding antibody assays may not accurately predict the risk of infection with new SARS-CoV-2 variants. In this study, we investigated the association between live virus neutralising antibody activity and SARS-CoV-2 infection risk using self-administered capillary microsample blood tests from VirusWatch participants. The study was conducted during the transition between the dominance of the B.1.617.2 (Delta) and B.1.1.529 (Omicron BA.1) SARS-CoV-2 variants, enabling us to investigate the association between variant-specific virus inhibition and subsequent infections within each dominance period. Greater inhibition of Omicron BA.1 live virus was associated with a reduction in infection risk during both the Delta and Omicron BA.1 dominance periods. Delta virus inhibition was associated with infection risk reduction during the Delta dominance period, but we found no association between Delta inhibition and protection against infection during the Omicron BA.1 dominance period. Our results are consistent with earlier findings and suggest that variant-specific serosurveillance of immunity and protection against SARS-CoV-2 infection at the population level could inform public health policy in near-real time using inexpensive and accessible home-based testing.