Association between COVID-19 vaccination status and mortality in hospitalised COVID-19 patients during the Omicron period: a retrospective cohort study in Taiwan

Abstract

Objectives The Omicron variant of SARS-CoV-2 has emerged as the predominant strain of COVID-19 since 2022. Its association with prior vaccines remained under investigation. Design Retrospective cohort study. Setting Clinical data for patients, from 1 May 2022 to 31 January 2023, were extracted from the Chi-Mei Medical Center, Chiali electronic medical record databases. Participants Hospitalised COVID-19 patients in dedicated wards were enrolled in the study. Cases of COVID-19 reinfection and relapse were also included. Patients who did not have COVID-19, those with PCR repositivity, or those with incomplete laboratory data were excluded. Interventions Various doses of vaccines included primary series, additional dose and booster. The types of vaccines included ChAdOx1-S, mRNA-based vaccines and recombinant protein vaccine. The interval between the last vaccination date and the diagnosis date of COVID-19 was assessed. Primary and secondary outcome measure The primary outcome was all-cause mortality by day 30. The secondary outcomes were severe disease of COVID-19 and 90-day survival. Results Among 469 cases, the adjusted HR for 30-day mortality in vaccinated compared with unvaccinated patients was 0.831 (95% CI 0.541 to 1.277; p=0.398), indicating no statistically significant association. Age, Charlson Comorbidity Index (CCI), quick Sequential Organ Failure Assessment score and administration of dexamethasone were recognised as powerful predictors for survival in multivariable analysis. In subgroup analysis, a statistically significant association with better 30-day survival was observed among patients aged <75 years and those with CCI <3. Conclusions Vaccination was associated with lower mortality in younger or low-CCI patients, but not in older or highly comorbid patients.