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Big Cities Have Longer Flu Seasons, While Small Cities Have More Intense Ones

New research reveals how city size and density affect the transmission of the flu virus.
A boy gets a flu shot at a health center in Decatur, Georgia, in February 2018.
A boy gets a flu shot at a health center in Decatur, Georgia, in February 2018.David Goldman/AP

Heading into flu season, predicting the virus’ spread and mapping where outbreaks might occur remains an imperfect science. But a new study says a surprising factor impacts how bad the season is: city size.

The study, published in the journal Science, finds that smaller cities like Nashville experience flu season differently than larger, denser metropolises, with shorter and more intense outbreaks of the disease that can strain public-health infrastructure. Accounting for the impact of humidity, the researchers also found that larger cities such as Miami and New York had flu seasons that started earlier and stretched into the spring, but with cases that were more spread out.