This claim is interesting because it contains a kernel of truth yet is framed in a sensational and potentially misleading way ("may increase the lifespan of cancer patients"). Recent research fro the University of Texas MD Anderson Cancer Center and others indicate that, in a retrospective observational study — cancer patients (specifically advanced lung cancer or metastatic melanoma) who received an mRNA-based COVID-19 vaccine within ~100 days of starting immunotherapy had substantially better median survival than those who did not: for example, ~37.3 months vs ~20.6 months in one cohort.
However, there are important caveats: the studies are retrospective (not randomized controlled trials), and the authors themselves caution that we can’t yet conclude causality. Thus the claim that “Covid vaccines may increase lifespan” is partially true (there is some evidence) but misleading if one presents it as definitive proof. A more accurate statement: “Preliminary observational evidence suggests mRNA COVID-19 vaccines might improve survival for cancer patients undergoing immunotherapy, but further clinical trials are needed.”
https://www.reuters.com/business/healthcare-pharmaceuticals/health-rounds-mrna-covid-vaccines-appear-make-immunotherapy-cancer-drugs-work-2025-10-22/