Spirulina has been studied in a small number of trials involving people with HIV or hepatitis C. This research does not show that spirulina prevents common viral infections or replaces antiviral treatment.
A 2024 review reported possible changes in viral load and CD4 counts across six studies, while an earlier Cochrane review found no consistent clinical or immunological benefit and concluded that firm conclusions could not be drawn. The studies differed in design, population and treatment context.
Spirulina should not be used to prevent or treat a viral infection and must not replace vaccination, testing or prescribed antiviral care.