Fluorescent Tissue Culture Infectious Dose 50% (fTCID50)

The fTCID50 assay is an adaptation of the classical TCID₅₀ method in which viral infection is detected using antigen‑specific immunofluorescence rather than CPE alone. Following infection of permissive cell cultures, viral replication is identified by staining for viral antigens using fluorescently labelled antibodies, enabling earlier and more sensitive detection of infected cells. This format is particularly useful for viruses that produce minimal or delayed CPE and allows increased assay robustness, throughput, and objectivity. Fluorescent TCID₅₀ assays are commonly applied to influenza viruses, RSV, human metapneumovirus, parainfluenza viruses, and other respiratory or non‑cytopathic viruses such as Hepatitis A virus, and—when appropriately validated—are suitable for use in regulated laboratory settings supporting vaccine development, antiviral evaluation, and potency or infectivity studies