New simulations reveal that the 2009 H1N1 pandemic and the 2020 COVID-19 spread rapidly across more than 300 US metro areas within weeks, often before officials registered an outbreak or intervened.[1] H1N1 caused 274,304 hospitalizations and 12,469 deaths in the US.[1] The study, published in the journal Proceedings of the National Academy of Sciences, is the first to compare the spatial transmission of the two pandemics at the metrolithic level.[1] Major travel hubs such as New York and Atlanta provided rapid nationwide transmission, with air travel playing a larger role than the daily commute.[1] Unpredictable and random patterns of spread made it difficult to predict outbreaks in real time.[1] The researchers used computer models with data on air traffic, human movement, and superdiffusion to reconstruct the spread.[1] The study highlights the importance of early detection systems to slow down future pandemics.[1] Other factors such as demographics, school schedules, or weather also affect the spread.[1]