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editorial
. 2021 Oct 30;20(3):1545–1551. doi: 10.1007/s10311-021-01346-0

Fig. 2.

Fig. 2

A metro station as in Paris, France, during the COVID-19 pandemic in February 2021, showing a large crowd of people waiting for the subway train. Although most people were wearing face masks, the efficacy of protection is questionable in the very crowded space with little physical distancing. During peak hours, it is impossible for commuters to keep the required six-foot social distance in public transport vehicles and waiting areas. Photo: copyright Eric Lichtfouse 2021