An international team of researchers has developed a computer model which can predict the timing and intensity of influenza outbreaks in subtropical climates like Hong Kong where flu seasons can occur at different times and more than once during a year.

Scientists at Columbia University’s Mailman School of Public Health and the School of Public Health of Li Ka Shing Faculty of Medicine at the University of Hong Kong used data, from a network of 50 outpatient clinics and laboratory reports in Hong Kong from 1998 to 2013, as a test case to retrospectively generate weekly flu forecasts.

The system forecasted both the peak timing and peak magnitude for 44 epidemics in 16 years caused by individual influenza strains, including influenza A (H3N2), influenza B, and both seasonal and the 2009 pandemic outbreaks of influenza A (H1N1).

Advance Warning

The technique predicted the peak timing of the outbreak three weeks in advance of the actual peak with accuracy as high as 93 percent. Says senior author Jeffrey Shaman, PhD, associate professor of Environmental Health Sciences at the Mailman School:

“These forecasts provide information at lead times that can be valuable for both the public and health officials. Individuals may choose to get a flu vaccine to protect themselves against infection, while officials can anticipate how many vaccines and other supplies are needed, as well as the number of clinicians and nurses needed."

Since the 2013-2014 season, the Mailman School scientists have published weekly regional flu forecasts for over 100 cities in the United States using a system recognized by the U.S. Centers for Disease Control and Prevention.

[caption id=“attachment_19755” align=“aligncenter” width=“700”]understanding influenza Credit: CDC/ Douglas E. Jordan[/caption]

Researchers expect to publish real-time predictions for Hong Kong in advance of the next influenza season, which will appear on the Prediction of Infectious Disease website (, and the Hong Kong group website (

Flu in the Subtropics

Seasonal influenza outbreaks in temperate climates like the United States are restricted to the winter months. By contrast, outbreaks in the subtropics such as Hong Kong happen year-round.

In addition, outbreak intensity, duration, and timing are more variable in the subtropics than in temperate regions. Says first author Wan Yang, PhD, an associate research scientist at the Mailman School:

“The irregularity of flu outbreaks in subtropical climates makes forecasting more challenging."

Going forward, the researchers hope to refine the system to account for cross-immunity due to prior infections from related strains, for varying transmission dynamics among age groups, or spatial connectivity among sub-regions.

Worldwide, influenza kills an estimated 250,000 to 500,000 people each year. In the U.S. (population 320 million) about 35,000 and in Hong Kong (population 7.2 million) about 750 die from the flu every year.

Yang W, Cowling BJ, Lau EHY, Shaman J (2015) Forecasting Influenza Epidemics in Hong Kong. PLoS Comput Biol 11(7): e1004383. doi:10.1371/journal.pcbi.1004383

Photo: “Influenza-Shock2009(1)” by MASA (talk) - GFDL(投稿者撮影). Licensed under CC BY-SA 3.0

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