Influenza, or flu, and air pollution are significant public health risks that impact nations around the world with large economic consequences. The authors of this paper show that increased levels of air pollution significantly increase the rate of hospitalisation for people with flu. In addition, they find that protection afforded by the flu vaccine greatly diminishes the relationship between air pollution and hospitalisation and reduces the social and medical costs of poor air quality. This suggests that seemingly disparate policy actions of pollution control and vaccination campaigns jointly provide greater returns than those implied by addressing either problem in isolation. The insights regarding compounding risks from pollution and flu may extend to other viral respiratory illnesses, including the current COVID-19 pandemic, and are also relevant for climate change policies given their significant overlap with air quality policies.