The infectious unit of influenza A virus is a population of particles, not a single virion, as shown by absolute particle quantification

Absolute particle quantification of influenza A virus A/Puerto Rico/8/1934 (H1N1) shows a count-to-PFU ratio of ~400, with infection saturating at pMOI 5–10.

• Why it matters: Influenza A virus stocks contain many non-infectious particles, but how incomplete viral genomes contribute quantitatively to productive infection has been unclear.
• What they did: The study used a digital influenza assay to measure particles and define particle-based MOI, then combined single-cell infection in microcompartments with automated cell classification across a wide pMOI range.
• The result: Infection rates followed a sigmoidal curve and saturated at pMOI 5–10, and modeling suggested stochastic functionality across eight genomic segments, robust across strains despite a 20-fold CTPR variation.

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