Meteorological conditions and nonpharmaceutical interventions jointly determined local transmissibility of COVID-19 in 41 Chinese cities: A retrospective observational study

Abstract

Background Before effective vaccines become widely available, sufficient understanding of the impacts of climate, human movement and non-pharmaceutical interventions on the transmissibility of COVID-19 is needed but still lacking. Methods We collected by crowdsourcing a database of 11 003 COVID-19 cases from 305 cities outside Hubei Province from December 31, 2019 to April 27, 2020. We estimated the daily effective reproduction numbers ( R t ) of COVID-19 in 41 cities where the crowdsourced case data are comparable to the official surveillance data. The impacts of meteorological variables, human movement indices and nonpharmaceutical emergency responses on R t were evaluated with generalized estimation equation models. Findings The median R t was 0•46 (IQR: 0•37–0•87) in the northern cities, higher than 0•20 (IQR: 0•09–0•52) in the southern cities ( p =0•004). A higher local transmissibility of COVID-19 was associated with a low temperature, a relative humidity near 70–75%, and higher intracity and intercity human movement. An increase in temperature from 0℃ to 20℃ would reduce R t by 30% (95 CI 10–46%). A further increase to 30℃ would result in another 17% (95% CI 5–27%) reduction. An increase in relative humidity from 40% to 75% would raise the transmissibility by 47% (95% CI 9–97%), but a further increase to 90% would reduce the transmissibility by 12% (95% CI 4–19%). The decrease in intracity human movement as a part of the highest-level emergency response in China reduced the transmissibility by 36% (95% CI 27–44%), compared to 5% (95% CI 1–9%) for restricting intercity transport. Other nonpharmaceutical interventions further reduced R t by 39% (95% CI 31–47%). Interpretation Climate can affect the transmission of COVID-19 where effective interventions are implemented. Restrictions on intracity human movement may be needed in places where other nonpharmaceutical interventions are unable to mitigate local transmission. Funding China Mega-Project on Infectious Disease Prevention; U.S. National Institutes of Health and National Science Foundation.

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