Importance . COVID-19 pandemic control measures affect the prevalence of other respiratory viruses . Effects on some viruses have been described; however, the broader impact and temporal relationship of control measures on virus decline and subsequent re-emergence have not been thoroughly documented . Understanding these phenomena may influence health policies . Objective . To examine the prevalence of unrelated respiratory viruses in relation to population-wide pandemic response measures and phases in 2020 in Singapore . Design, Setting, and Participants . Data from respiratory multiplex PCRs from 3 major hospitals (total 3700 beds) in Singapore were collated . The full dataset consisted of 42,558 test results , 19,898 from 2019 and 22,660 from 2020 . Main Outcomes and Measures . Weekly virus prevalence data were mapped onto prevailing pandemic response measures, in order to elucidate temporal relationships and differential virus responses . Pre-pandemic data from 2019 were compared with data from 2020 . Results . Early response measures, even before national lockdown, were followed by a dramatic reduction of influenza viruses and a more gradual decline of other respiratory viruses, including respiratory syncytial virus, parainfluenza viruses, endemic coronaviruses and metapneumovirus . Marked decline of enterovirus/rhinovirus and adenovirus, however, was only observed during lockdown . About 13 weeks into phased reopening, enterovirus/rhinovirus re-emerged, followed by adenovirus, the latter mainly in the pediatric population . All other viruses remained at low levels until the end of 2020 . Conclusions and Relevance . COVID-19 control measures in Singapore had a significant impact on a broad range of respiratory viruses . Effects of various control measures varied between phases and different viruses . Influenza viruses declined earliest and most dramatically; relaxation of measures was followed by re-emergence of enterovirus/rhinovirus and adenovirus . These patterns are presumably a result of different propensities for contact versus droplet and overall ease of transmission, and different virus reservoirs . Further studies into these phenomena are a matter of public health importance.