New research adds to the early evidence that seasonal weather variations which drive influenza outbreaks are playing a role in the spread of Covid-19.
Findings from two newly published studies suggest that higher temperatures and increased humidity are factors in slowing the spread of the disease.
High humidity has been shown in numerous studies to protect against seasonal flu outbreaks, and the two studies suggest that high humidity may also reduce the transmission of the Covid-19 virus SARS-CoV-2.
In a study of climate impact in the early spread of Covid-19 in Spain, published June 9 in the journal Geographical Analysis, warmer temperatures and higher humidity were associated with reduced spread of the virus.
Researcher Antonio Paez, of McMaster University, Ontario, and colleagues, estimated that for each 1% increase in temperature and humidity, a 3% reduction in viral transmission would occur under normal, non-lockdown, conditions.
However, increased sunlight was associated with higher viral spread, which the researchers attributed to increased social interaction and less social distancing on sunnier days.
Higher temperatures and higher humidity also appeared to protect against SARS-CoV-2 spread in a 50 city climate data study conducted during the early months of the SARS-CoV-2 outbreak, published June 11 in JAMA Network Open.
Researchers compared climate data from 8 cities with substantial spread of Covid-19 from January to March 10, 2020 to 42 cities that did not see substantial community spread during this period.
They found that the 8 cities (Wuhan, China; Tokyo; Daegu, South Korea; Qom, Iran; Milan; Paris; Seattle and Madrid) were all located on a narrow geographical band along the 30° to 50° N corridor. These cities also had consistently similar weather patterns during the winter months examined, with temperatures between 5° and 11° C (41° to 52° F) and low specific and absolute humidity.
Cities located at latitudes above or below the 30° to 50° N corridor had lower spread of the virus during these months than would have been expected based on proximity to the outbreak cities, wrote researcher Mohammad Sajadi, MD, of the University of Maryland School of Medicine, and colleagues.
In an interview with BreakingMED, Sajadi said climate and seasonality are just one of many potential factors associated with the spread of SARS-CoV-2, with social distancing interventions, travel patterns, population density and other variables all playing a role.
“Transmission is multifactorial, but temperature and humidity may give us some guidance about when areas have the highest potential risk,” he said.
Sajadi added that using weather modeling, it may be possible to estimate the regions most at risk for community spread of Covid-19 in the months to come.
He noted that within the continental United States, most cities are projected to experience temperature and humidity drops associated with increased spread of Covid-19 in late Sept. and early Oct.
“We can basically predict the start of (seasonal) influenza spread when there is a sudden drop in humidity,” he said. “We don’t yet know if this is also true with Covid-19, but it may be.”
Sajadi and colleagues called for research integrating epidemiological earth-human system models, “which can incorporate climate and weather processes and variables (e.g., dynamics of temperature, humidity) and their spatiotemporal changes as well as simulate scenarios of human interactions (e.g., travel, transmission due to population density).
“Such models can assimilate data currently being collected to accelerate the improvements of model estimations on short time scales (ie, daily to seasonally),” they wrote. “This approach would allow researchers to explore questions such as which population centers are most at risk and for how long; where to intensify large-scale surveillance and tighten control measures to prevent spreading; how to better understand limiting factors for virus spreading in the southern hemisphere; and how to make estimations for the 2021 to 2022 virus season.
“A better understanding of the cause of seasonality for coronavirus and other respiratory viruses would undoubtedly aid in better treatments and/or prevention and be useful in determining which areas need heightened surveillance.”
- Higher temperatures and increased humidity appear to be associated with reduced spread of SARS-CoV-2, two newly published studies found.
- Eight cities with early Covid-19 outbreaks were all located on a narrow geographical band along the 30° to 50° N corridor. These cities also had consistently similar weather patterns during the winter months examined, with temperatures between 5° and 11° C (41° to 52° F) and low specific and absolute humidity.
Salynn Boyles, Contributing Writer, BreakingMED™
Funding for this research was provided by the U.S. National Institutes of Health.
The researchers reported no relevant conflicts of interest related to this study.
Cat ID: 190
Topic ID: 79,190,254,930,500,932,190,926,192,927,151,928,925,934