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New study cautions against relying on COVID-19's weather seasonality

By Mark Puleo, AccuWeather staff writer

Updated Apr 7, 2021 11:18 AM EDT

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Health officials warn that amid the spread of variants, the US could be on the cusp of a fourth surge in COVID-19 cases.

Over a year has passed since COVID-19 shook up the world as we know it and while many studies have provided many answers, huge questions still linger. What makes the virus easier to transmit in some places and more deadly in others? Can the environment lend a helping hand, or is it all up to us to stomp out the pandemic?

Dozens of studies have been conducted hoping to discover which piece of Mother Nature's puzzle may match the needed edges to eradicate transmission or at least provide a bit of optimism and glimmers of hope for a return to normalcy.

Now in the second calendar year of learning and adjusting for the virus, a task force from the World Meteorological Organization (WMO) has determined that its government policy influences that are likely to have the biggest impact on viral transmission, not the weather.

“If you depend too much on seasonality to help you, then you are basically helping the disease transmit," Ben Zaitchik, chair of the WMO taskforce, told AccuWeather. "We’ve seen that this disease is fully capable of transmitting effectively in every climate zone and is fully effective of transmitting in every season."

People have a drink on the seaside in Saint Jean de Luz in Saint Jean de Luz, southwestern France, Thursday, April 1, 2021. France's prime minister Jean Castex on Thursday defended new nationwide measures to combat a resurgent coronavirus in France that include closing schools for at least three weeks and putting in place a month-long domestic travel ban, the government has acted "consistently and pragmatically."(AP Photo/Bob Edme)

Zaitchik and the WMO's COVID-19 research task force's findings not only uncovered more about the behavior of COVID-19, but how the seasonality of endemic diseases in general is understood.

In comparing the virus to a fire, COVID-19 can be counted on to burn if given the opportunity to spread, with human behaviors being the most flammable of fuels.

As the Northern Hemisphere races toward the second summer of the pandemic, there just isn’t any evidence to support loosening of restrictions or a rapid reopening on the basis of the seasonality, he said.

For example, a wintertime peak in the U.S. may not have been a surprise by environmental standards because of how endemic diseases behave in colder conditions, but the same can't be said about countries that had similarly timed spikes in the Southern Hemisphere.

With viral infections, such as the flu or various types of coronaviruses, Zaitchik explained that seasonality with a virus is believed to be exhibited with viruses in one of three ways, each representing a different camp of thought.

The first being that the virus itself doesn't like particular weather conditions, thus it can become more difficult for transmission in certain conditions. Another is that a person's immune systems may not function as well under certain weather conditions, which can make people more susceptible to viruses in certain seasons.

Finally, the third camp of thought is that human behavior changes during different seasons, thus making transmission more dependent on social patterns.

Students listen during a class by Kyle Faircloth, Associate Professor of Intercultural Studies, at Palm Beach Atlantic University, Friday, Feb. 26, 2021, in West Palm Beach, Fla. University President Dr. Debra Schwinn said that they had to decide last summer whether to reopen campus or stick solely with online learning. (AP Photo/Wilfredo Lee)

But because of the shift in human behaviors to spend much more time indoors rather than outdoors, Zaitchik said commonly held hypotheses regarding the behavior of seasonality have been challenged and patterns revealed by this novel coronavirus have shed more light on our understanding.

This is where Zaitchik and his team's findings lean, concluding that the spread of COVID-19 is much more likely influenced by the seasonality of human behaviors rather than seasonality of weather conditions.

"What we've seen this past year with COVID is interesting because, to me, it really pushes it towards behavior,” Zaitchik said. “Obviously with the dominance of enforced or voluntarily adopted behavioral restrictions, that's clear, but even if you look at the seasonality" it points to behavior playing a larger role than weather.

For evidence, Zaitchik pointed to the Christmas-time case spike reported in the U.S., which environmentally would make sense because it was during the winter, but the same can't be said for the Christmas-time surge in South Africa.

Zaitchik pointed out that even when you dig in closer and examine seasonality, it's difficult to separate weather and human factors in the transmission of COVID-19, but there is some data that suggest human behavior may play more of a role than the weather. For example, if you look at wintertime in the United States, coronavirus cases were rampant around Christmas, with over 200,000 new cases recorded nearly every day of December and the daily count even reached 300,000 in early January.

This 2020 electron microscope image made available by the U.S. Centers for Disease Control and Prevention shows the spherical particles of the new coronavirus, colorized blue, from the first U.S. case of COVID-19. Antibody blood tests for the coronavirus could play a key role in deciding whether millions of Americans can safely return to work and school. But public health officials warn that the current “Wild West” of unregulated tests is creating confusion that could ultimately slow the path to recovery. (Hannah A. Bullock, Azaibi Tamin/CDC via AP)

However, across the Atlantic Ocean and in the Southern Hemisphere, South Africa also witnessed a notable spike after the Christmas holiday, as the country had its most intense days of new transmissions fall in the first week of 2021. The nation's 16 highest single-day infection spikes all fell between Jan. 23 and Feb. 16, topping out at nearly 22,000 new cases on Jan. 8.

These trends in the data kept raising one question for Zaitchik: "Will we eventually see some kind of seasonality emerge with this disease?" He thinks, perhaps we may, but since the virus is still so new and spreading in populations without herd immunity and so much volatility, what we will see sooner are the influences of human behavior.

Beyond the roller coaster of virus seasonality that experts have tried to chase for the past year, Zaitchik raised a deeper concern about an environmental factor that he doesn't think is receiving its proper attention. In his studies, poor air quality may be the deadly, underlying link that bears more focus.

Poor air quality may explain why the disease has been more severe in some places than others, Zaitchik said.

"The fact that chronic exposure to poor air quality showed up within months as a risk factor for death from COVID-19 is yet another reminder of how important air quality is and how egregious the environmental injustices are in its disparities," he said.

A woman wearing a face mask to help curb the spread of the coronavirus stands against the China Central Television (CCTV) building as capital city is hit by polluted air and a sandstorm in Beijing, Monday, March 15, 2021. The sandstorm brought a tinted haze to Beijing's skies and sent air quality indices soaring on Monday. (AP Photo/Andy Wong)

Zaitchik called the lack of focus on air quality "really troubling" because of how important the component has shown to be in influencing the virus's deadliness.

While there is much more left to be understood about its overall impacts on severity, Zaitchik said, the connection is clear. One aspect he said he longs to better understand is whether air quality is causing people to have weaker respiratory systems before infection or if poor air quality complicates symptoms after infection.

In fact, according to Zaitchik's findings, there might be evidence for both chronic and acute impacts.

"When it comes to severity of the disease, from everything we’ve seen, air pollution is going to be much more predictive than anything having to do with meteorology," he said.

A woman wearing a face mask reacts from a sandstorm as she walks across a street in Beijing, Monday, March 15, 2021. The sandstorm brought a tinted haze to Beijing's skies and sent air quality indices soaring on Monday. (AP Photo/Andy Wong)

But regardless of the order in which air quality causes its destruction, the findings from Zaitchik's team still clearly point the finger at government policies as playing a far more important role than weather factors.

While it may be impossible to quantify the size of that role, the lessons learned from a disastrous 2020 can hopefully shape the way we respect and adapt policies regarding the virus in 2021, he said.

Policies in countries such as in New Zealand and Australia showed that the virus can be eliminated by behavior changes, he said, and the inverse was also learned the hard way elsewhere.

In New Zealand, swift policy changes such as fierce border-control changes, a long-term national shutdown and strict contact tracing of all residents has nearly eliminated the spread of the virus entirely in the country. Since May, the nation hasn't had a single day with more than 31 new cases.

But those changes will need to be dictated by policies, he said, and not the over-reliance on weather.

"I think what we learned in 2020 is that these kinds of changes in behavior really have a massive impact," Zaitchik said. "This thing can be squashed... effectively through behaviors and so I think it’s a positive message that, that this is a disease that we can control if we want to and if those kinds of interventions work."

Related:

Coronavirus pandemic and weather: A one-year look back
More sunlight equals less COVID transmission, new study suggests
What if COVID actually arrived in the US far earlier than we currently think?
Heat and relative humidity affect how coronavirus spreads, new study finds

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