Effectiveness of COVID-19 vaccines administered in the 2023 autumnal campaigns in Europe: Results from the VEBIS primary care test-negative design study, September 2023-January 2024

Abstract

In autumn 2023, European vaccination campaigns predominantly administered XBB.1.5 vaccine. In a European multicentre study, we estimated 2023 COVID-19 vaccine effectiveness (VE) against laboratory-confirmed symptomatic infection at primary care level between September 2023 and January 2024. Using a test-negative case-control design, we estimated VE in the target group for COVID-19 vaccination overall and by time since vaccination. We included 1057 cases and 4397 controls. Vaccine effectiveness was 40 % (95 % CI: 26-53 %) overall, 48 % (95 % CI: 31-61 %) among those vaccinated < 6 weeks of onset and 29 % (95 % CI: 3-49 %) at 6-14 weeks. Our results suggest that COVID-19 vaccines administered to target groups during the autumn 2023 campaigns showed clinically significant effectiveness against laboratory-confirmed, medically attended symptomatic SARS-CoV-2 infection in the 3 months following vaccination. A longer study period will allow for further variant-specific COVID-19 VE estimates, better understanding decline in VE and informing booster administration policies.

Keywords: COVID-19; Europe; Multicentre study; SARS-CoV-2; Test-negative design; Vaccine effectiveness.

Fig. 1

Patients included in the VEBIS primary care study by COVID-19 case status and ISO week of symptom onset, Europe, September 2023–January 2024 (n = 5,454). ISO: International Organisation for Standardisation; VEBIS: Vaccine Effectiveness, Burden and Impact Studies.

Fig. 2

COVID-19 vaccine effectiveness^a against medically-attended symptomatic SARS-CoV-2 infection among target groups for vaccination, (A) overall against any SARS-CoV-2 and against Omicron XBB and its sublineages and (B) against any SARS-CoV-2 stratified by age-specific vaccination target groups, Europe, VEBIS primary care study, September 2023–January 2024. Abbreviations: VEBIS: Vaccine Effectiveness, Burden and Impact Studies. The series of numbers below the x-axes provides the number of vaccinated cases; number of cases / number of vaccinated controls; number of controls. ^a All VE models included study site, sex and presence of chronic condition as adjustment variables. Using the Akaike information criterion to select the best functional form of onset date and age for each VE model, we included onset date as a restricted cubic spline (RCS) with 3 or 4 knots depending on the analysis, and age as a RCS with 3 or 5 knots, as a continuous variable or as a categorical variable with 5-year age bands depending on the analysis. ^b The target groups for older adults varied by country, see Table 1.

Fig. 2

COVID-19 vaccine effectiveness^a against medically-attended symptomatic SARS-CoV-2 infection among target groups for vaccination, (A) overall against any SARS-CoV-2 and against Omicron XBB and its sublineages and (B) against any SARS-CoV-2 stratified by age-specific vaccination target groups, Europe, VEBIS primary care study, September 2023–January 2024. Abbreviations: VEBIS: Vaccine Effectiveness, Burden and Impact Studies. The series of numbers below the x-axes provides the number of vaccinated cases; number of cases / number of vaccinated controls; number of controls. ^a All VE models included study site, sex and presence of chronic condition as adjustment variables. Using the Akaike information criterion to select the best functional form of onset date and age for each VE model, we included onset date as a restricted cubic spline (RCS) with 3 or 4 knots depending on the analysis, and age as a RCS with 3 or 5 knots, as a continuous variable or as a categorical variable with 5-year age bands depending on the analysis. ^b The target groups for older adults varied by country, see Table 1.