Air pollution, viral spread and health outcomes evidence from strikes in France

To evidence the impact of air pollution on the health of urban populations, several studies use natural experiments that shift commuting from public transport to cars (or vice-versa). However, as public transport use declines, reduced interpersonal contact may lead to slower virus spread and thus lower respiratory morbidity. Using a difference-in-differences strategy, we show that respiratory hospitalisations are both positively affected by air pollution and negatively affected by viral spread following partial unavailability of public transport due to strikes in the ten most populated French cities during the period 2010–2015. Our results are in line with studies in other countries that have found a significant increase in urgent respiratory hospitalisations following a public transport strike, most likely due to car pollution, but we also find a detectable interaction with viral spread, which should not be overlooked when interpreting these studies.