Journal Article

High vaccine effectiveness against severe COVID-19 outcomes and population preventable fraction during the Omicron era in Luxembourg: A nationwide retrospective risk factor analysis

Vergison, Anne, Stranges, Saverio, Mossong, Joël, Ernst, Corinna, Zeegers, Maurice P., Bejko, Dritan

2024

Overview

•Residents infected with COVID-19 between December 2021 and March 2023 in Luxembourg were enrolled in a nationwide retrospective cohort study.•Complete primary vaccination conferred 49.5% protection against death, one booster 69.0%, and two boosters 76.2%•Complete primary vaccination conferred 38.8% protection against hospitalization, one booster 62.1%, and two boosters 71.6%•The vaccination against COVID-19 lowered mortality by 55.8% and hospital admissions by 49.1%. Luxembourg experienced major consecutive SARS-CoV-2 infection waves due to Omicron variants during 2022 while having achieved a high vaccination coverage in 2021. We investigated the risk factors associated to severe outcomes (i.e., hospitalisation, deaths) and estimated vaccine effectiveness (VE) as well as the role of immunity conferred by prior infections against severe outcomes in adults. We linked reported SARS-CoV-2 cases among residents aged ≥ 20 years with vaccination data and SARS-CoV-2 related hospitalisations and deaths. Cases were followed-up until day 14 for COVID-19 related hospital admission and up to day 28 for mortality after a positive test. We analysed the association between the vaccination status and severe forms using proportional Cox regression, adjusting for previous infection, age, sex and nursing homes residency. VE was measured as 1-adjusted hazard ratio of vaccinated vs unvaccinated individuals. The population preventable fraction was computed using the adjusted hazard ratio and the proportion of cases within the vaccination category. Between December 2021, and March 2023, we recorded 187143 SARS-CoV-2 cases, 1728 (0.93%) hospitalizations and 611 (0.33%) deaths. The risk of severe outcomes increased with age, was higher among men and nursing home residents. Compared to unvaccinated adults, VE against hospitalization was 38.8% (95%CI: 28.1%-47.8%) for a complete primary cycle of vaccination, 62.1% (95%CI: 57.0%-66.7%) for one booster, and 71.6% (95%CI: 66.7%-76.2%) for two booster doses. VE against death was respectively 49.5% (95%CI: 30.8%-63.3%), 69.0% (95%CI: 61.2%-75.3%) and 76.2% (95%CI: 68.4%-82.2%). Previous infection was not associated with lower risk of hospitalisation or mortality. The vaccination lowered mortality by 55.8 % (95%CI: 46.3%-62.8%) and reduced hospital admissions by 49.1% (95%CI: 43.4%-54.4%). Complete vaccination and booster but not previous infection were protective against hospitalization and death. The vaccination program in Luxembourg led to substantial reductions in SARS-CoV-2-related mortality and hospitalizations at the population level.

• Publisher: Elsevier Ltd,Elsevier Limited
• Subject: Adult / Adults / Age / Age groups / Aged / Aged, 80 and over / Allergy and Immunology / COVID-19 / COVID-19 - epidemiology / COVID-19 - immunology / COVID-19 - mortality / COVID-19 - prevention & control / COVID-19 infection / COVID-19 vaccines / COVID-19 Vaccines - immunology / Death / Disease transmission / Drug dosages / Effectiveness / Factor analysis / Fatalities / Female / hazard ratio / Hospital admission / Hospitalization / Hospitalization - statistics & numerical data / Hospitals / Humans / immunity / Infections / Luxembourg / Luxembourg - epidemiology / Male / Middle Aged / Mortality / Natural immunity / Nurses / Nursing homes / regression analysis / Retrospective cohort / Retrospective Studies / Risk Factors / SARS-CoV-2 - immunology / Severe acute respiratory syndrome coronavirus 2 / Sex ratio / Vaccination / Vaccination Coverage - statistics & numerical data / Vaccine effectiveness / Vaccine Efficacy / Vaccines / Young Adult