Airborne dominance in COVID-19 transmission on long-haul flights

Abstract

The COVID-19 pandemic underscored the heightened risk of respiratory virus transmission in enclosed, densely populated environments. Aircraft cabins represent a unique setting, combining high ventilation and high-efficiency particulate air (HEPA) filtration with persistent uncertainty regarding dominant transmission routes. Using data from a documented long-haul in-flight outbreak, we developed a multi-route mechanistic model with Bayesian inference to quantify contributions of airborne, direct deposition, and contact transmission. Airborne transmission dominated, accounting for a median of 92.2% (95% credible interval [CrI]: 83.6–96.5%), whereas contact (7.8%, 95% CrI: 3.5–16.4%) and direct deposition (0.0%, 95% CrI: 0.0–0.1%) played minimal roles. Passengers seated within two rows of the index case had a 4.41-fold higher attack rate compared with those farther away (95% confidence interval [CI]: 1.98–9.81, P < 0.001), which our model reproduced through a simulated 5.00-fold (95% CrI: 2.10–12.86) higher risk in the same zone. Notably, 45% of observed infections occurred beyond this proximity, with our model predicting a comparable proportion (40%), indicating that long-range airborne transmission can persist even in highly ventilated cabins and underscoring limitations of contact tracing protocols. These findings provide quantitative evidence for SARS-CoV-2 transmission mechanisms in aircraft cabins and yield insights to guide risk assessment and infection control strategies in enclosed environments.