Coronavirus pandemic and weather: A one-year look back

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As the world marks one year since the World Health Organization designated the coronavirus outbreak a global pandemic, a look back at the past 12 months shows how much has been learned about how the virus is structured, how it spreads and how it behaves. Yet some weighty questions linger: Mainly, how did we get here?

Many signs and data points suggest the weather may influence the coronavirus to some degree, but to what degree remains something of a mystery. Since the world as we knew it ground to a halt last March, dozens (if not hundreds) of different studies have been published analyzing the many different weather influences on COVID-19. While each publication has shed some amount of new light on the topic, the overall picture remains murky at best.

However, as the end of winter nears, caseloads across the United States have gradually receded in recent weeks. Glimmers of hope twinkle that in the coming months, a mix of warmth and sunshine could offer the environmental aid needed to supplement human efforts at slowing and eventually stopping the transmission of the virus.

"It's tough to say exactly how big of a puzzle piece (seasonality) is, but I am personally looking forward to summer," researcher Jonathan Proctor told AccuWeather in January. "I have a little bit of optimism."

Visitors hold their hands out to receive the sun's energy as they celebrate the Spring equinox atop the Pyramid of the Sun in Teotihuacan, Mexico, Wednesday, March 21, 2018. Although the official vernal equinox occurred on Tuesday, thousands of visitors were expected to climb the ancient pyramid Wednesday to greet the sun and celebrate the beginning of Spring. (AP Photo/Rebecca Blackwell)

Proctor and his fellow authors from Harvard University and University of California Santa Barbara shared their findings on the impacts of seasonality on COVID-19 in December and certainly weren't the first researchers to try to better understand that link.

Going all the way back to last March, experts were keenly aware that some specific weather conditions were likely to play some role in the pandemic's impact. Linsey Marr, an aerosol scientist at Virginia Tech, explained to AccuWeather at the very beginning of the pandemic that the spread of coronavirus can be compared to second-hand smoke.

At the time she said that, the U.S. had never seen a day with more than 10,000 new cases.

"I think as the weather warms up and our humidity indoors gets higher, we'll have to see. We can hope that transmission might slow down, but I don't think we can count on it," Marr said on March 23, 2020.

Marr's doubt proved fatally true. More than half a million COVID-19 deaths later, worldwide, it's been proven that human behavior perhaps plays a much larger role than environmental factors in influencing viral spread. By July, daily caseload increases in the U.S. were regularly topping 70,000 new infections, more than double what they were in April. This rise in cases also coincided with the U.S. significantly ramping up capacity to test for the illness.

Come winter, when many of those environmental aids were replaced by a season of gray and snow, those daily cases had multiplied fourfold, topping out at 299,786 new infections on Jan. 2 alone. But was it just the weather that sent new infections surging? Those rising caseloads also coincided with the Thanksgiving and Christmas holidays, occasions in which many Americans ignored health officials' calls to social distance and traveled in some cases to different parts of the country.

But untangling which forces -- weather conditions, government restrictions or human behavior -- are most dominant in this equation has proven highly difficult for researchers.

In this Wednesday, March 18, 2020 file photo, a man wearing a face mask to prevent the spread of coronavirus travels by train in Barcelona, Spain. When the World Health Organization declared the coronavirus a pandemic one year ago Thursday, March 11, it did so only after weeks of resisting the term and maintaining the highly infectious virus could still be stopped. A year later, the U.N. agency is still struggling to keep on top of the evolving science of COVID-19, to persuade countries to abandon their nationalistic tendencies and help get vaccines where they're needed most. (AP Photo/Emilio Morenatti, file)

Comparing the size of impacts weather can make compared to human behaviors may be a nearly impossible task to quantify, but experts such as Proctor and Bryan Lewis, a professor with the Biocomplexity Institute at the University of Virginia, say Americans need to stick to the basics first and then hope the helpful weather can arrive as an aid.

"COVID is kind of both really difficult and simple at the same time," Proctor said, advising that people "keep doing the basics of wearing a mask. If you have to see someone, see them outdoors ... Quantitatively, when comparing the full effect of seasonality of winter to summer in the Northern or Southern Hemisphere, that affect appears to be a third to a sixth the size of social distancing policies."

Lewis told AccuWeather's Monica Danielle in January that those basics have proven effective, as seen by the vast reduction of flu cases this winter. The seasonal flu, another virus that is largely influenced by the weather, is spreading at record-low rates this winter in the U.S., and experts are crediting the mask-wearing and social distancing for keeping the flu at historic lows.

However, Lewis also emphasized that the flu and the coronavirus behave, spread and impact the population in much different ways.

The flu season typically runs from October to March, with some active cases lasting into May. But this year, it's just nowhere to be found, Lynette Brammer, who leads the domestic influenza team for the Centers for Disease Control and Prevention (CDC), told AccuWeather in February.

"The flu season this year has been pretty nonexistent, and I really do think that has a lot to do with the levels of precautions folks are talking, just the extra social distancing we're engaged in has eliminated flu transmission over this season," Lewis said. "COVID-19, the SARS-CoV-2 virus, is extremely more transmissible than the flu and has a lot worse outcomes as well and its been able to find a way to continue transmitting, but the flu has just been fully interrupted by people wearing masks, staying home, the reduced number of children in schools and I think more people got the flu vaccine as well."

In this Saturday, Oct. 17, 2020, file photo, University of Southern California student pharmacist candidate Whitney Fakolade prepares a single dose of influenza vaccine during L.A. Care Health Plan and Blue Shield of California Promise Health Plan's Community Resource Center's Free Drive-Thru vaccination event at the Exposition Park in Los Angeles. New government data suggests more Americans have been getting flu shots in 2020, apparently heeding the advice of health officials fearful of a flu/coronavirus double pandemic. (AP Photo/Damian Dovarganes, File)

Lewis said the spread of vaccines will be crucial in order for the environmental benefits in slowing COVID to be recognized going forward. He likened that process to the end of winter combining with the protection provided by flu vaccines in order to curb the spread of influenza.

Earlier this month, President Joe Biden announced that a vaccine would be available for every adult in the U.S. by the end of May, a timeline that would align nicely with the year's peak sunshine months of summer. Similar to Lewis and Proctor, Biden said in his announcement that the vaccines represent a "light at the end of the tunnel" but also cautioned that Americans wouldn't let their guards down.

The vaccine rollout process over the past three months has been difficult from a logistical standpoint. Adding to that, strictly in a practical sense, weather events certainly haven't helped. Multiple major snowstorms in cities such as Chicago, New York City and Philadelphia have held up vaccination efforts while the massive winter storm that shut down Texas for a week in February also halted testing and vaccination administrations.

Looking ahead, Lewis reiterated that the environment can't be fully relied upon to be the COVID killer like many might have hoped a year ago. But when coupled with the ongoing basic sanitation efforts and increased vaccination doses, greater hopes lie ahead.

"We do have to just brace ourselves that there is a long way to go before we have sufficient vaccinations to induce herd immunity and allow us to go back to normal," he said, adding that Americans need to stick to those basics in order to drive down prevalence. "Hopefully, by the time spring arrives and we get some assistance from Mother Nature, we'll be at a very low prevalence, and we then can start to move back into a normal life."

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