Because timing of pandemic onset was geographically asynchronous in Peru (Figure 1) , we explored the association between pandemic onset, demographic factors, and absolute humidity in the 134 provinces. At the province level, the timing of the pandemic onset was moderately and significantly associated with population density (Spearman rho = 20.44, P = 0.03; Figure D in Text S1). There was no significant association between the timing of the pandemic and population size (rho = 20.25, P = 0.23) or distance from Lima City (rho = 0.31, P = 0.13). Moreover, timing of pandemic onset at the province level was not associated with a decline in absolute humidity levels within 30 days of onset (Spearman rho = 0.16-0.30, P.0.14, Figure E in Text S1).