Booster timing — not just vaccination status — drives COVID-19 death risk in immunocompromised patients

For patients with immune-mediated rheumatic diseases, staying current on COVID-19 boosters could be a matter of life and death. A nationwide retrospective study from Brazil found that the longer a patient went without a booster, the higher their risk of dying in the hospital from COVID-19. Crucially, it wasn't about whether they were vaccinated or how many total doses they'd received — it was specifically about how long ago their last booster was.

The study, presented at ACR Convergence 2026, analyzed 918 hospitalized patients from Brazil's national surveillance system between 2022 and 2024. Overall in-hospital mortality was 36% across the study period, declining from 38% in 2022 to 26% in 2023 before ticking back up to 28% in 2024.

By the Numbers:

• 28% — in-hospital mortality rate in 2024 for this patient group
• OR = 1.97 — odds of death for patients with a longer gap since last booster
• OR = 4.89 — odds of death for patients requiring ICU admission
• OR = 2.22 — elevated mortality risk for Black patients compared to other groups

Why it matters: Clinicians managing immunocompromised patients need to track not just vaccination history, but recency of the last booster. While the study can't yet define an optimal booster interval, it sends a clear signal: for this vulnerable population, letting too much time pass between boosters may carry serious consequences.