The COVID-19 pandemic it has spread rapidly, and this fact was pronounced in the temperate regions of the northern hemisphere, coinciding with winter. The number of cases reported in countries in tropical regions was lower. Till the date, the spread of COVID-19 has been minimal in high-income southern hemisphere countries such as Australia and New Zealand, which were in their summer season when the first cases were reported in late January and February, respectively.
Much has been speculated on whether warmer temperatures are associated with less transmission of COVID-19, similar to what is seen in many viral respiratory infections. It was shown that Higher temperatures have a protective effect against the transmission of severe acute respiratory syndrome from 2002-2003, possibly due to the lower survival of SARS-CoV on surfaces at higher temperatures. Decreased droplet spread when speaking at higher temperatures is another possible mechanism, as seen for human influenza viruses, although their role in the transmission of SARS-CoV-2 remains unclear.
Several studies have investigated the association between time variation (mainly temperature and humidity) and the spread of COVID-19. However, there are several important limitations of the studies published to date. First, the existing ones have not distinguished between imported and locally acquired infections. This is potentially a major source of bias in the analyzes, as imported infections are not related to weather conditions in the place where they are detected. For example, 62.5% of COVID-19 cases in Australia (May of this year) were acquired abroad, and the proportion was even higher at the beginning of the pandemic. Secondly, most studies have not taken into account variation in the ability to detect emerging infections; This is particularly relevant for interpreting data on the spread of COVID-19 in the first weeks of the pandemic.
Finally, no study has performed a global analysis using aggregated COVID-19 data consistently at the subnational level, reflecting the limitations of current reports. For example, a recent global analysis had COVID-19 data available at the city, province and country levels. The country-level measurements were compared with meteorological data for the capital city, which masks significant meteorological variations that can occur within countries.
Thermometers and forecasts
Currently, consistent global datasets on COVID-19 cases, or public health interventions implemented in response to the pandemic, are not available at the subnational level. This significantly limits efforts to disentangle the effects of climate variation from those produced by public health interventions since the widespread lockdowns and other substantial control measures began. However, detailed COVID-19 data from the first weeks of the pandemic, before the massive lockdown implementation, could be informative to understand the association between COVID-19 and climate variation.
A partially complete open-line global list of all COVID-19 cases reported since inception, including detailed location and epidemiological information for each case has enabled in he study carried out by a group of professionals from Ausvet Europe, Lyon in France, the objective was to analyze seasonal variation taking into account the limitations of existing studies.
In March the list of lines contained Detailed data on 26,032 cases, of which 25,861 had a valid confirmation date entry and were used for analysis. This document provides new evidence of the impact of climate-related parameters on the incidence of COVID-19 cases. There was a statistically significant effect of the average air temperature during the previous three weeks on the incidence of infections as recorded in this study. However, the effect size was quite small. The incidence of the COVID-19 case was negatively correlated with air temperature for temperatures above -15 ° C. It should be noted that the effect of relative humidity was not statistically significant.
This study provides evidence that there may be seasonal variability in the transmission of SARS-CoV-2, but this analysis does not imply that temperature alone is a major driver of COVID-19 transmission. The observed association may not be directly due to temperature.
More heat, less COVID-19?
Countries with the highest early detection capacity had an increasing incidence of reported cases. Specialists suggest that this association “is due to a detection bias, where countries with better disease testing capacity simply register more cases.”
Current reports on the pandemic show that almost every country in the world has been affected by SARS-CoV-2, despite the great variation in their ability to prevent, detect and respond to disease outbreaks. However, the opposite association was expected, where countries with higher early detection capacity would have fewer cases due to their ability to implement control measures earlier.
There are several strengths in this presented analysis, which add to the evidence base for an association between climate variation and COVID-19. The most important thing is that This study used detailed data from the online list, allowing the first global analysis of COVID-19 cases at the provincial or state level, and for the categorization of cases as local or imported.
Temperature and humidity have also been considered factors that influence the spread of pandemic influenza. and other respiratory tract viruses. This condition tends to show few seasonal trends at the time of emergence, while seasonal patterns appear during later waves. These patterns have been linked to more efficient transmission in cold and dry climates. However, many other factors related to the host, the virus and the environment are likely to be involved. “Our results – they say – regarding the effect of temperature on the incidence of COVID-19 are consistent with some of these characteristics. The possibility of a similar recurrence and seasonality has been suggested for SARS-CoV-2, although caution should be exercised before extrapolating the observed characteristics for pandemic influenza to the COVID-19 pandemic ”.
The final conclusion indicates evidence of a modest association between warmer temperatures and lower COVID-19 incidence, for reported cases globally. Thus, Warmer weather may modestly reduce the spread rate of COVID-19. These findings do not justify transmission due solely to temperature with the onset of summer.
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