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This article investigated whether the atmospheric temperature had any
role in the spread and vulnerability to COVID-19 worldwide and how that
knowledge can be utilized to contain the fast-spreading disease. It
highlighted that temperature was an important factor in transmitting the
virus, and a moderately cool environment was the most favourable state
for its susceptibility. In fact, the risk from the virus is reduced
significantly in high temperature environment. Warm countries and places
were likely to be less vulnerable. We identified various degrees of
vulnerability based on temperature and specified countries for March and
April. The maximum reported case, as well as death, was noted when the
temperature was in the range of around 275°K (2°C) to 290°K (17°C).
Countries like the USA, UK, Italy and Spain belonged to this category.
The vulnerability was moderate when the temperature was less than around
275° K (2° C) and countries in that category were
Russia, parts of Canada and few Scandinavian countries. For temperature
300° K (27° C) and above, a significantly lesser degree
of vulnerability was noted. Countries from SAARC, South East Asia, the
African continent and Australia fell in that category. In fact, when the
temperature was more than 305° K (32° C), there was a
unusually low number of reported cases and deaths. For warm countries,
further analyses on the degree of vulnerability were conducted for the
group of countries from SAARC and South East Asia and individual
countries were compared. We also showed countries can switch from one
vulnerability state to another based on the variability of temperature.
We provided maps of temperature to identify countries of different
vulnerability states in different months of the year.
That influence of temperature on the virus and previous results of
clinical trials with similar viruses gave us a useful insight that
regulating the level of temperature can provide remarkable results to
arrest and stop the outbreak. Based on that knowledge, some urgent
solutions are proposed, which are practically without side effects and
very cost-effective too.
Introduction:
The recent pandemic of COronaVIrus Disease 2019 (COVID-19) and its rapid
spread worldwide1,2 brought the whole human
civilization to a standstill. The responsible virus for the disease is
Severe Acute Respiratory Syndrome CoronaVirus 2
(SARS -CoV -2 ) 3. Detailed
analysis of the characteristics of the virus and the nature of the
disease is outlined in current research4, 5.
The disease first originated in the Wuhan Province of China. The case of
hospital admission was first reported on 12th December
2019 and since then till 15th March there were 80,995
reported cases in China with 3,203 confirmed deaths2.
Various analyses on the COVID-19 spread in China were detailed in a
recent study6. That figure all over the globe reached
1,000,249 and 51,515 respectively2 on
3rd April 2020, since 31 December 2019. Geographic
distribution of COVID-19 cases worldwide are presented in Fig.1a.
Because of the highly contagious in nature 3,7, most
of the countries worldwide started lockdown situation from around third
week of March8.
Several facts highlighted that the spread of recent Coronavirus pandemic
showed some geographical preferences (Fig.1). Countries and cities with
moderately cold winter temperature indicated a rapid spread (UK, Italy,
Spain, northern USA etc.) compared to warm countries (e.g., countries
from the African continent, Indian subcontinent and, Australia)1,2. Moreover, very cold countries like Canada, Russia
and Scandinavian countries only showed moderate severity. Interestingly,
the countries that suggested moderate severity started showing the sign
of more severity from the end of April. More importantly, it is
happening in spite of a global lockdown situation. Over the same time,
some warm countries (e.g, Brazil, Chilli) also suggested a rise in
severity1,2.
On a regional basis, compared to warmer places, colder regions were seen
more affected. During February and January 2020, a sub-zero minimum
temperature was noted in the Wuhan province of China where the outbreak
was reported first. Wuhan experienced maximum severity in terms of the
death toll and the rapid rise of infected patients. In February this
year, the following cities (Rome in Italy, Tehran in Iran, Seoul in
South Korea) all experienced a sub-zero minimum temperature and
coincidentally showed a sharp increase in the number of infected
patients. Those cities were the epicentres of the outbreak of respective
countries. The numbers of infected people in Italy, Iran, South Korea
are reported to be 115242, 50468 and 10062 (as of 3rdApril 2020 since 31 December 2019) 2.
Close connections between epidemics and seasons are previously
identified for mid-latitude temperate regions; which is November till
March in the Northern Hemisphere, while May upto September in the
Southern Hemisphere 9,10,11. In temperate regions,
absolute humidity minimizes in winter alongside temperature which
becomes more susceptible to certain virus transmission and
survival10.
A laboratory study using a seasonally dependent endemic virus that has
close resemblance with Coronavirus also confirmed the dependence of
temperature and humidity on the spread of disease11.
It showed that at a temperature of 5 ºC and relative humidity (RH) 35%
to 50% the infection rate was very high (75-100%). Whereas, when the
RH was still kept at 35%, but only temperature was increased to 30°C
the infection rate surprisingly reduced to zero11. As
the infection rate was reduced to zero at temperature 30 °C and humidity
35% that estimation may be useful for arresting spread of similar
viruses and needs further exploration.
Another virus named the Middle East Respiratory Syndrome Coronavirus
(MERS-CoV) that share genetic similarity with COVID-19 was shown to
remain active for a long time in low humidity and low
temperature12. Studies with a different Coronavirus
SARS-CoV (Severe Acute Respiratory Syndrome Coronavirus) also noted the
same connection 13,14,15. MERS-CoV and SARS-CoV both
belong to the Coronavirus genus in
the Coronaviridae family16.
Research also studied strength and activity for a similar generic
Coronavirus (viz. SARS-CoV) using a variable level of temperature and
humidity14. It found that inactivation of the virus
was faster at all humidity level if the temperature was simply raised to
20°C from 4°C. Also, the inactivation was more rapid if the temperature
was further increased to 40°C from 20°C, suggesting the virus is
extremely sensitive to high temperature . SARS could, however, be active
for at least five days in typical airconditioned environments which has
relative humidity 40-50 % and room temperature 22 -25°C13. The strength of the virus was lost rapidly when
relative humidity was >95% and temperatures were 38°C or
higher13. Studies with various Coronavirus generic
categories other than MERS and SARS also confirmed that low temperature
significantly contributes to the survival and transmission of the
virus14,17.
COVID-19 is an extremely contagious disease 3,7 as it
invaded almost all parts of the globe in less than two
months1,2. The nature of its transmission under
variable temperature condition also needs attention. A lab experiment
was conducted using guinea pigs to examine the contamination of a
similar seasonal air-borne virus11. It studied the
effect of temperature on airborne transmission as well as contact
transmission. Increasing the temperature prevented airborne transmission
but could not stop contact transmission. When guinea pigs were kept in
separate cages for 1 week at a temperature of 30°C, no infection took
place among recipient guinea pigs. But to simulate contact transmission,
if those were kept in the same cage, between 75% and 100% became
infected. They, however, found no role of humidity in these experiments.
Though the knowledge of temperature sensitivity to the similar seasonal
virus is recognised, whether any early warning systems can be proposed
on various space and time scales is yet to be
determined18. The role of weather on the spread of
COVID-19 was also studied in various analyses. Research confirmed
dependencies on temperature and humidity 14,15 ; wind
speed and surface pressure19 for the spread of virus.
A systematic review to understand the effect of temperature on COVID-19
was also conducted21 . It collected numerous recent
journal submissions (around 16 in number) and almost all of them
indicated a strong dependence on temperature. There are potential that
the knowledge of such analyses can be used for the benefit of human
society in the current emergency situation. The role of global
temperature on the transmission of COVID-19 worldwide was mentioned
first by the author in a recent work 22. That
knowledge was further elaborated in a subsequent study by presenting a
global temperature spatial map and comparing with vulnerability
worldwide23. The current analysis is an extension work
to investigate that effect further. It also identifies countries that
are more vulnerable/ favourable than others in various seasons.
It is an extremely contagious disease3,7 and has very
high epidemic potential. Scientists from different fields are working
tirelessly to mitigate the crisis. Clinical trials and laboratory
experiments are time consuming. Lockdown and social distancing can be a
temporary solution, as the economy and mental health also need
attention. With those emergency situations in mind, some effective
solutions are proposed. These additional measures, apart from existing
guidelines 3,7 , can greatly benefit to overcome the
crisis.
This article is based on the idea whether the variable global
temperature has any role in the transmission of virus globally and to
arrest the rapidly spreading disease, how that knowledge can be used.
Methodology and Data:
We analysed global air temperature data from NCEP/NCAR Reanalysis
product24, a joint product from the National Center
for Atmospheric Research (NCAR) and National Centers for Environmental
Prediction (NCEP). The data is freely available25. It
has a temporal coverage of Monthly as well as Daily values from 1948
January till recent dates. The long-term monthly mean of this data is
available and derived for years 1981 - 2010. The spatial coverages
extend all over the globe and has 17 vertical levels. In this analysis,
we only considered the lowest level near the surface which is 1000mb.
For air temperature, we calculated climatology (30 years average), as
well as some daily composites using compositing technique. We also used
the Method of Mean Differences to analyse the result and to find
differences between two sets of data. The level of statistical
significance was derived using the student’s t-test. Data related to
COVID-19 are freely available and all listed underneath.