Ecuador was an early COVID-19 hotspot with substantial COVID-19-mortality. In developed countries, low socioeconomic status is associated with COVID-19 infection and low compliance with non-pharmaceutical interventions (NPIs). However, if NPI were successful in resource-limited settings with high human mobility and informal labour is still unclear. We performed a retrospective observational molecular and serological study of Ecuador’s reference laboratory. We tested 1,950 respiratory samples from COVID-19 surveillance for SARS-CoV-2 and 12 respiratory viruses using RT-PCR, characterized 642 SARS-CoV-2 genomes, and examined SARS-CoV-2 seroprevalence in 1,967 samples from patients with fever in Ecuador’s reference laboratory during 2020-2021. Molecular and serological data were compared to NPI stringency in Bayesian, maximum-likelihood and modelling frameworks.SARS-CoV-2 (Pearson correlation test; r=-0.74; p=0.01) and other respiratory viruses (r=-0.68; p=0.02) detection correlated negatively with NPI stringency. SARS-CoV-2 seroprevalence increased from