COVID-19 vaccine effectiveness against progression to in-hospital mortality — Zambia, 2021-2022

Background COVID-19 vaccines are highly effective for reducing severe disease and mortality. However, vaccine effectiveness data is limited from sub-Saharan Africa, where SARS-CoV-2 epidemiology has differed from other regions. We report COVID-19 vaccine effectiveness against progression to in-hospital mortality in Zambia. Methods We conducted a retrospective cohort study among admitted patients at eight COVID-19 treatment centers across Zambia during April 2021 through March 2022. Patient demographic and clinical information including vaccination status and hospitalization outcome (discharged or died) werecollected. Multivariable logistic regression was used to assess the odds of in-hospital mortality by vaccination status, adjusted for age, sex, number of comorbid conditions, disease severity, and COVID-19 treatment center. Vaccine effectiveness of ≥1 vaccine dose was calculated from the adjusted odds ratio. Results Among 1,653 patients with data on their vaccination status and hospitalization outcome, 365 (22.1%) died. Overall, 236 (14.3%) patients had received ≥1 vaccine dose before hospital admission. For patients who had received ≥1 vaccine dose, 22 (9.3%) died compared with 343 (24.2%) among unvaccinated patients (p <0.01). The median time since receipt of a first vaccine dose was 52.5 days (IQR: 28-107). Vaccine effectiveness for progression to in-hospital mortality among hospitalized patients was 64.8% (95% CI: 42.3-79.4%). Conclusions Among patients admitted to COVID-19 treatment centers in Zambia, COVID-19 vaccination was associated with lower progression to in-hospital mortality. These data are consistent with evidence from other countries demonstrating benefit of COVID-19 vaccination against severe complications. Vaccination is a critical tool for reducing the consequences of COVID-19 in Zambia. Key points ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work has been supported by the Zambia Ministry of Health and the U.S. President's Emergency Plan for AIDS Relief (PEPFAR) through the U.S. Centers for Disease Control and Prevention (CDC) and the CDC Emergency Response to the COVID-19 pandemic. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study protocol was approved by the University of Zambia Biomedical Research Ethics Committee; it was also reviewed in accordance with the US Centers for Disease Control and Prevention (CDC) human research protection procedures and was determined to be research, but CDC investigators did not interact with human subjects or have access to identifiable data or specimens for research purposes. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors