Y.HAO1, L.W.ANG1, E.M.J.SOON1, I.C.BOUDVILLE1, Y.S.LEO1, M.P.H.S.TOH1
National Centre for Infectious Diseases1
Singapore rolled out its COVID-19 vaccination programme on 30 December 2020, with priority given to persons at high risk of infection and those vulnerable to severe disease. The more transmissible Delta (B.1.617.2) variant has become the dominant circulating strain in Singapore since late April 2021. The objective of this retrospective observational study is to compare disease severity of COVID-19 cases by vaccination status.
COVID-19 cases admitted to the National Centre for Infectious Diseases from 28 April to 11 July 2021 who had been discharged, decanted or died as of 14 July 2021 were included. We applied a multivariable logistic regression to examine the association between vaccination status and COVID-19 severity, as defined by supplementary oxygen requirement.
331 COVID-19 patients were included, of whom 88.2% had whole genome sequencing results (291 Delta and 1 Beta variant). Median age was 46 years (interquartile range 32 to 64). 42.6% had received at least one vaccine dose. 18.9% of non-vaccinated patients required supplementary oxygen compared with 3.5% who had been vaccinated with at least one dose. The predicted probability of supplementary oxygen requirement increased exponentially with age in non-vaccinated patients. Compared with non-vaccinated patients, the odds of supplementary oxygen requirement were 98% (95% CI: 89% to 100%) and 74% (95% CI: 25% to 93%) lower in the fully vaccinated and partially vaccinated groups respectively after adjustment for age.
Elderly persons are at higher risk of severe COVID-19 disease. Full COVID-19 vaccination is highly protective against severe disease across all ages.