Hotter weather slows, but does not halt spread of most viruses

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COLUMBUS, Ohio (WCMH) — The global outbreak of the coronavirus (SARS-CoV-2) responsible for COVID-19 is linked to the absence of immunity, and is spreading much faster than a similar acute viral respiratory illness caused by the SARS coronavirus pathogen (SARS-CoV), which first appeared in southern China in November 2002.

COVID-19 cases are increasing rapidly in the U.S. through community spread, after initially being associated with travelers who were exposed to the virus in another country.

Dr. Iahn Gonsenhauser, Chief Quality and Patient Safety Officer at Wexner Medical Center, Internal Medicine, said, “In the winter months, obviously runny noses, a lot more coughing, a lot more congestion, a lot more bodily secretion that are hard to control — that’s the primary spread for viruses.”

The seasonal flu typically peaks in the winter, although transmissions still occur in the summer, but at a significantly reduced rate. The peak period for viruses such as influenza in the Northern Hemisphere occurs between November and April.

Experts caution that there is no way of predicting whether the spread of the novel coronavirus, which resembles the flu but has a much higher reproduction rate (a single COVID-19 carrier potentially infects between 2 and 3 other people), will be mitigated by warmer weather.

Gonsenhauser added, “As far as the weather goes, we really don’t see weather as a necessary implication for flu patterns for viral respiratory patterns, or for viruses in general.”

Cases of the novel coronavirus have been fewer in subtropical and equatorial regions such as Singapore, and in the Southern Hemisphere, where it’s currently autumn, although these regions are also less populous, reducing opportunities for community spread. Densely populated India is on a 21-day coronavirus lockdown.

The temperature itself is not the primary factor, because most viruses and bacteria are comfortable at our normal body temperature. A fever is how the body tries to kill the virus or bacteria and stimulate the immune system.

However, several studies have shown that viruses tend to survive longer in colder, drier conditions (lower humidity), and are easily passed on from host to host, largely because we are more cooped up compared to the late spring and summer.

The increasing sun angle in late spring and summer and in the mid-latitudes of North America and Europe allows more sunlight (ultraviolet light) to reach the surface, which interferes with the transmission and replication of viruses responsible for the common cold and influenza. Ultraviolet light can disrupt the essential structure (DNA or RNA) of viruses. The additional sunlight also provides us with more Vitamin D, which balances our immune system.

However, not all viruses exhibit the same pattern, or any at all. Tuberculosis and polio outbreaks hit harder in warmer climates. A further challenge for medical experts when it comes to predicting a seasonal pattern is that the novel coronavirus outbreak this year started later in the wintertime in China and South Korea than previous epidemics.

There are four coronaviruses that cause the common cold and tend to wane in the warmer months. The slower-moving SARS (2002-2003) epidemic and H1N1 swine flu (2009-2010), peaked in the colder months before fading by summertime.

There are similarities between the novel coronavirus and the SARS virus, which started in China and killed 774 people and infected 8,098 around the world. The number of cases fell sharply in Asia by summer, and was largely controlled in the U.S. in late spring.

The Spanish flu pandemic in 1918, which killed an estimated 50 million people or more worldwide (675,000 in the U.S.), declined in summer, but was followed by a huge and deadly fall resurgence. This occurred after the return home of World War I troops from across the Atlantic, after the Allied victory in November 1918.

Gonsenhauser stressed the current uncertainties about the pattern of the novel coronavirus. “This is new. We haven’t seen this specific pathogen before, so it’s hard to really predict. Anecdotally speaking, when we look at other coronaviruses they tend to wane in the warmer summer months, so we would expect the same about this one as well.”

“Seasonally we do see some changes, and historically and anecdotally what I can reference is that we do typically see a drop off in coronavirus, the typical coronavirus that we have seen in the past. So, not the novel coronavirus, but in typical coronavirus, we have seen a pretty significant drop off as we move out of the winter months and into the warmer months,” Gonsenhauser explained.

The cautious hope among scientists and medical experts is that the seasonal return of warm, humid weather in the Northern Hemisphere and at least several months of social distancing will stem the tide of the coronavirus.

COVID-19 is an upper respiratory illness or infection that can be accompanied by a fever, chills in period that varies from hours to days, and can lead to a life-threatening Acute Respiratory Distress Syndrome. The symptoms can be mild and confused for allergies or a common cold, or not evident at all in someone who is carrier.

“The best distinguishing feature is if you come into contact with somebody, direct contact with somebody who has been diagnosed, or is exhibiting signs and sympotms of COVID-19,” Gonsenhauser said. The novel virus is more easily spread than most coronaviruses in past epidemics.

“It depends which data set you look at. MERS and SARS were 6 to 8 percent mortality range. Be careful how you’re interpreting it because it’s still outstanding. But, if you look at South Korea which has the most complete data set, they’ve ended up at about 0.5% mortality, which is significantly lower than what we’re seeing elsewhere,” Gonsenhauser said.

Even as the weather warms, the best advice is to just keep washing your hands and monitoring your symptoms diligently, because little is known about the novel coronavirus. And experts note that even if it diminishes in the summer, it is impossible to predict whether it will return in the autumn with comparable severity.

Copyright 2020 Nexstar Broadcasting, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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