Trump's denials didn't help
Columbia University's Mailman School of Public Health
Both outbreaks had major consequences in the United States.
The 2009 H1N1 flu pandemic led to 274,304 hospitalizations and 12,469 deaths.
The COVID-19 pandemic has been even more devastating, with 1.2 million
confirmed deaths reported so far.
Modeling the Spread Across Cities
The researchers aimed to understand how these pandemics
traveled geographically in order to improve planning for future outbreaks. To
do this, they combined detailed information about how each virus spreads with
computer models that accounted for air travel, everyday commuting, and the
possibility of superspreading events. Their analysis focused on more than three
hundred metropolitan areas across the U.S.
Rapid Expansion Before Early Warnings
The simulations revealed that both pandemics were already
circulating widely in most metro areas within just a few weeks. This widespread
transmission often occurred before early case detection or government response
measures were in place. Although H1N1 and COVID-19 followed different routes
between locations, both relied on shared transmission hubs, including major
metro areas such as New York and Atlanta. Air travel played a much larger role
than commuting in driving this rapid spread. At the same time, unpredictable
transmission patterns added significant uncertainty, making it difficult to
anticipate where outbreaks would emerge in real time.
"The rapid and uncertain spread of the 2009 H1N1 flu
and 2020 COVID-19 pandemics underscores the challenges for timely detection and
control. Expanding wastewater surveillance coverage coupled with effective
infection control could potentially slow the initial spread of future
pandemics," says the study's senior author, Sen Pei, PhD, assistant
professor of environmental health sciences at Columbia Mailman School.
Wastewater Surveillance and Pandemic Preparedness
Previous research has highlighted the value of wastewater
surveillance as an early warning tool. This new study adds further support,
showing that expanding wastewater monitoring could play an important role in
improving pandemic preparedness and slowing early transmission.
Lessons Beyond H1N1 and COVID-19
In addition to reconstructing the spread of the last two
pandemics, the researchers developed a flexible framework that can be used to
study the early stages of other outbreaks. While human movement, especially air
travel, is a major driver of pandemic spread, the team notes that other factors
also influence how outbreaks unfold. These include population demographics,
school calendars, winter holidays, and weather patterns.
The study's first author is Renquan Zhang, Dalian University
of Technology, Dalian, China. Additional authors include Rui Deng and Sitong
Liu from Dalian University of Technology; Qing Yao and Jeffrey Shaman from
Columbia University; Bryan T. Grenfell from Princeton; and Cécile Viboud from
the National Institutes of Health.
For more than ten years, Jeffrey Shaman and colleagues,
including Sen Pei, have worked to improve methods for tracking and simulating
the spread of infectious diseases such as influenza and COVID-19. Their
real-time forecasting tools estimate how quickly outbreaks grow, where they are
likely to spread, and when they may peak, helping guide public health
decision-making.
- Renquan
Zhang, Rui Deng, Sitong Liu, Qing Yao, Jeffrey Shaman, Bryan T. Grenfell,
Cécile Viboud, Sen Pei. Reconstructing the early spatial spread of
pandemic respiratory viruses in the United States. Proceedings
of the National Academy of Sciences, 2026; 123 (2) DOI: 10.1073/pnas.2518051123
