Impact of COVID-19 Vaccination on Patients with Non-Small Cell Lung Cancer Receiving First-Line Immune Checkpoint Inhibitor Therapy: Real-World Evidence from Romania

Background: The interaction between COVID-19 vaccination and immune checkpoint inhibitor (ICI) therapy in advanced non-small cell lung cancer (NSCLC) remains incompletely characterized. Methods: Retrospective cohort study of 139 patients with stage IV NSCLC treated with first-line ICI-based therapy, stratified by vaccination status and total doses received (0–1 vs. ≥2). Progression-free (PFS) and overall survival (OS) were analyzed by Kaplan–Meier and Cox regression; logistic regression explored factors associated with treatment-related toxicity. Results: Vaccinated patients had longer median PFS (13.0 vs. 11.0 months) and OS (29.0 vs. 24.0 months; both p < 0.001). In multivariable models these associations were attenuated and of borderline significance (OS HR = 0.83, 95% CI 0.69–0.99; PFS HR = 0.79, 95% CI 0.62–0.99). Outcomes were also more favorable with ≥2 doses (median PFS 14.0 vs. 12.0 months, p = 0.001; median OS 30.0 vs. 24.0 months, p < 0.001), and tumor mutational status was the strongest independent predictor of survival. In an exploratory model, ≥2 doses were associated with higher odds of any-grade toxicity (OR = 2.47, p = 0.037); events were predominantly low grade, with no Grade 4 or 5 toxicity. Conclusions: COVID-19 vaccination was associated with improved PFS and OS in stage IV NSCLC receiving first-line ICI therapy, with a dose-related pattern. The association was attenuated after adjustment for tumor biology and is hypothesis-generating. These findings support the safety and potential clinical relevance of vaccination in this population and underline the need for structured monitoring during immunotherapy. Prospective validation is required.