Changing Prevalence of Immunocompromising Conditions in Patients Hospitalized with Severe Acute Respiratory Infection in Europe: Insights from the COVIDRIVE Study

Background
Immunocompromised individuals are at substantially increased risk of severe acute respiratory infection (SARI), often compounded by inadequate response to vaccination. We assessed the prevalence of immunocompromising conditions (ICs) among hospitalized SARI patients, overall and by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) status, focusing on temporal trends during the coronavirus disease 2019 (COVID-19) pandemic. We hypothesized that IC prevalence among SARS-CoV-2-positive SARI patients may have increased over time due to increasing background rates of SARS-CoV-2 exposure and differential vaccination coverage and efficacy among those with IC.

Methods
We conducted a secondary data analysis of 5280 adults (≥ 18 years) hospitalized with SARI, enrolled in the COVIDRIVE study from five hospitals in Belgium, Italy, and Spain (June 2021-May 2023) and tested for SARS-CoV-2 by reverse transcription-polymerase chain reaction (RT-PCR). IC prevalence (including 95% confidence intervals [CIs)] was assessed using two definitions (main and alternative), excluding and including cancer patients. Changes in IC prevalence over time were assessed using linear trend analysis.

Results
Among the 5280 SARI cases, IC prevalence by main definition was 13.9% (95% CI: 12.9–14.8) overall, increasing from 8.3% (95% CI: 3.7–15.8) to a peak of 22.0% (95% CI: 17.9–26.4) in Q3 2022; by alternative definition, IC prevalence was 28.8% (95% CI: 27.6–30.0) overall, increasing from 18.8% (95% CI: 11.5–28.0) to a peak of 38.5% (95% CI: 32.7–44.5) in Q2 2023. Among the 1924 SARS-CoV-2-positive cases, IC prevalence by main definition was 14.2% (95% CI: 12.7–15.9) overall, increasing from 3.4% (95% CI: 0.1–17.8) to a peak of 23.8% (95% CI: 17.4–31.1) in Q3 2022; by alternative definition, IC prevalence was 29.6% (95% CI: 27.6–31.7) overall, increasing from 3.4% (95% CI: 0.1–17.8) to a peak of 46.8% (95% CI: 32.1–61.9) in Q2 2023. The larger observed increase in IC prevalence (by both definitions) over time among SARS-CoV-2-positives, relative to SARI patients without SARS-CoV-2, was statistically significant.

Conclusions
Immunocompromised individuals represent a high proportion of hospitalized SARI cases, with results suggesting IC prevalence was higher during later periods of the COVID-19 pandemic. As immunocompromised individuals often respond inadequately to vaccination, alternative strategies are needed to better protect this vulnerable group.