Background: Respiratory protective equipment recommended in the UK for healthcare workers (HCWs) caring for patients with COVID-19 comprises a fluid resistant surgical mask (FRSM), except in the context of aerosol generating procedures (AGPs). We previously demonstrated frequent pauci- and asymptomatic SARS-CoV-2 infection HCWs during the first wave of the COVID-19 pandemic in the UK, using a comprehensive PCR-based HCW screening programme (Rivett et al., 2020; Jones et al., 2020). Methods: Here, we use observational data and mathematical modelling to analyse infection rates amongst HCWs working on “red” (COVID-19) and “green” (non-COVID-19) wards during the second wave of the pandemic, before and after the substitution of filtering face piece 3 (FFP3) respirators for FRSMs. Results: Whilst using FRSMs, HCWs working on red wards faced an approximately 31-fold (and at least 5-fold) increased risk of direct, ward-based infection. Conversely, after changing to FFP3 respirators, this risk was significantly reduced (52-100% protection). Conclusions: FFP3 respirators may therefore provide more effective protection than FRSMs for healthcare workers caring for patients with COVID-19, whether or not AGPs are undertaken. Funding: Wellcome Trust, Medical Research Council, Addenbrooke’s Charitable Trust, NIHR Cambridge Biomedical Research Centre, NHS Blood and Transfusion, UKRI.