Background : As management and prevention strategies against Coronavirus Disease-19 (COVID-19) evolve, it is still uncertain whether prior exposure to immune checkpoint inhibitors (ICIs) affects COVID-19 severity in patients (pts) with cancer.

Methods : In a joint analysis of ICI recipients from OnCovid (NCT04393974) and ESMO CoCARE registries, we assessed severity and mortality from SARS-CoV-2 in vaccinated and unvaccinated pts with cancer and explored whether prior immune-related adverse events (irAEs) influenced outcome from COVID-19.

Results : The study population consisted of 240 pts diagnosed with COVID-19 between Jan 2020 and Feb 2022 exposed to ICI within 3 months prior to COVID-19 diagnosis, with a 30-day case fatality rate (CFR₃₀) of 23.6% (95%CI: 17.8-30.7%). 42 (17.5%) were fully vaccinated prior to COVID-19 and experienced decreased CFR₃₀ (4.8% vs 28.1%, p=0.001), hospitalization rate (27.5% vs 63.2%, p<0.001), requirement of oxygen therapy (15.8% vs 41.5%, p=0.003), COVID-19 complication rate (11.9% vs 34.6%, p=0.004), and COVID-19-specific therapy (26.3% vs 57.9%, p=0.001) compared with unvaccinated pts. IPTW-fitted multivariable analysis, following a clustered-robust correction for the data source (OnCovid vs ESMO CoCARE), confirmed that vaccinated pts experienced a decreased risk of death at 30 days (aOR 0.08, 95%CI: 0.01-0.69). 38 pts (15.8%) experienced at least 1 irAE of any grade at any time prior to COVID-19, at a median time of 3.2 months (0.13-48.7) from COVID-19 diagnosis. IrAEs occurred independently of baseline characteristics except for primary tumour (p=0.037) and were associated with a significantly decreased CFR₃₀ (10.8% vs 26.0%, p=0.0462) additionally confirmed by the IPTW-fitted multivariable analysis (aOR: 0.47, 95%CI: 0.33-0.67). Pts who experienced irAEs also presented a higher median absolute lymphocyte count at COVID-19 (1.4 vs 0.8 10⁹ cells/L, p=0.009).

Conclusions : Anti-SARS-CoV-2 vaccination reduces morbidity and mortality from COVID-19 in ICI recipients. History of irAEs might identify pts with pre-existing protection from COVID-19, warranting further investigation of adaptive immune determinants of protection from SARS-CoV-2.