RESUMEN
Approximately 75% of the UK population has received only one dose of a 2-dose COVID-19 vaccine regime in the face of circulating SARS-CoV-2 Variants of Concern (VOCs). We aimed to determine the levels of vaccine-induced neutralising antibodies to SARS-CoV-2 variants B.1.1.7, B.1.351 and P.1. To do so, we undertook a single-centre cross-sectional study of health care workers (HCWs) and outpatients with immunodeficiencies (IDP) based at the same critical care tertiary NHS Trust, following a single dose of either BNT162b2 or AZD1222 vaccines. Data revealed low neutralising antibodies (nAbs) in IDPs, with only 5% and 3% showing detectable neutralisation of B.1.1.7 and B.1.351, respectively. In contrast, healthy HCWs without a prior SARS-CoV-2 infection demonstrated a wide range of nAb titres post-vaccination with responses significantly lower than HCWs with prior SARS-CoV-2 infection. Neutralisation of VOCs with the E484K mutation (B.1.351 and P.1) were consistently lower in HCWs in the absence of evidence of prior SARS-CoV-2 infection (p<0.001). Notably, in vaccinated HCWs with prior SARS-CoV-2 infection, there was a significant increase of neutralising titres post-vaccination to all variants, compared to their pre-vaccination neutralisation titres. This underscores the importance of vaccination to boost neutralising antibody breadth to VOCs, and also provides support for the hypothesis that repeated immunisations will boost protective immunity in individuals without prior SARS-CoV-2 exposure.