As fall temperatures settle in across the United States, flu cases are bound to pop up again after seemingly vanishing for the spring and summer months, but with the coronavirus pandemic now surging across the country, flu season this year could become even more tricky to navigate than usual.
The flu season in the Northern Hemisphere typically begins in October, but it usually does not pick up until sometime in December. The peak of flu season usually occurs in February and continues into March, and influenzalike activity can last as late as May.
In the Southern Hemisphere, however, because the seasons are shifted, flu outbreaks can begin in June and September. According to The New York Times, the original name of the virus -- influenza di freddo, in Italian -- is inspired by the cold conditions with which it's associated, and translates to "influence of the cold."
And when cold air masses plunge down from Canada and the Arctic during winter, humidity levels go much lower than they are in the warmer months.
"There's a lot of evidence that the lower humidity allows the virus to be more efficient in transmission," Bryan Lewis, a professor at the Biocomplexity Institute at the University of Virginia, said of the spread of influenza during the winter. "And behaviorally, people tend to gather a bit more inside when it's cold out." However, he explained in an interview with Accuweather, flu cases can also spike in areas that are inconsistent with cold weather factors.
AccuWeather Long-Range Meteorologist Paul Pastelok said that environmental factors play a significant role in the spread of influenza, as students are in school for months on end in closed classrooms -- compared to warmer months when more time is spent outdoors -- which makes it easier to catch an illness through bodily contact or germs spread through coughing.
School children then come down with the flu and pass it along to parents, and those cases could become serious depending on a person's health and age. He said the same process of transmission can occur with adults in work environments as well.
The flu "forms a backbone of tradition" in school environments and within children, Lewis said, so increased social distancing and closed schools and office spaces could potentially lead to a more mild flu season overall.
"The flu will be affected by the measures that are in place to keep COVID at bay," Lewis said. "We've never had a flu season where a fair number of people are actually wearing masks when they go out in public. We've never had a flu season where a good portion of schools are in a hybrid model," he added.
"I certainly think that will play a role and will diminish the flu."
Lewis said there is a lot of evidence the coronavirus will behave in the same way as the flu in terms of spiking cases in the winter. He explained that there are many different coronaviruses that behave similarly to the flu each year that are usually what cause a runny nose in the winter.
"There is a lot of work done that did look at where some of the more tropical areas weren't having as explosive a growth in that early phase as some of the more northern latitudes," Lewis said.
In addition, some of the recent spikes in cases can be linked to a pattern with cold air causing temperatures to drop.
"If you sort of look at mean temperatures over the last month and the places that are spiking [in cases], there are some visual correlations there," he said. Lewis also pointed out that behavioral factors play a significant role in transmission, and a community with high mask usage compared to a community with low mask usage in the same climate will likely not see the same level of spread.
Along with the weather cooling, there is also the matter of the sunlight that people in the Northern Hemisphere are exposed to decreasing by the day as the calendar marches toward winter. The days are getting shorter and the intensity of the sunlight is diminishing until it reaches the low point on the winter solstice.
"We must be extraordinarily cautious and vigilant in the next several weeks as we move closer to the winter solstice on Dec. 21 when the daylight hours and the daily amount of sunshine are the shortest," AccuWeather Founder and CEO Dr. Joel N. Myers said. "As AccuWeather reported last spring, the daily dose of sunshine on June 21, the summer solstice, is 10 times what it is on Dec. 21 if you are out in the sun all day long."
Myers explained that "this lack of sunshine, combined with the bad winter weather when people spend more time indoors where they are closer together and air does not circulate as well as it does outdoors, which can lead to a higher viral load, especially in confined indoor spaces, will set us up for greater spread of the coronavirus, unfortunately."
With new coronavirus cases in the U.S. showing no signs of stopping, nurse manager in the Department of Medicine at Johns Hopkins Hospital Neysa Ernst said getting a flu shot is essential.
"The challenge is that you're not going to really know what you have in some cases because they are so very similar for some people," Ernst told AccuWeather. "So again, having that flu shot will rule [the flu] out pretty well."
As COVID-19 cases surged in the U.S. right before the flu season began, Ernst said the situation is what medical professionals call a "twindemic."
"You sort of have both of these events that could converge," she explained. "Yes, we're afraid of a COVID resurgence, but eyeing the flu on top of that will be really challenging."
According to the U.S. Centers for Disease Control and Prevention (CDC), some key differences between the coronavirus and the flu are that the coronavirus is more easily spread, it can be much more severe for some individuals, people can be contagious and show symptoms for a longer duration of time than with the flu, and there is no vaccine yet approved for the coronavirus, though two developmental vaccines -- one made by Pfizer and another by Moderna -- have shown to be more than 90% effective in clinical trials, the two drugmakers have said in recent days.
But, as Myers pointed out, "the actual implementation of widespread vaccinations could be months away, so people must be aware of these other weather-related factors that will almost certainly impact their health and wellbeing during this critical period of colder weather."
Despite the differences, many symptoms appear to be similar for both viruses, including fever, chills, cough, shortness of breath or difficulty breathing, fatigue, sore throat, runny or stuffy nose, muscle pain and body aches, headache, vomiting and diarrhea, although the last two are mostly seen with children.
"If you haven't had a flu shot and you feel these symptoms, go and ask your physician if you can get a COVID test," Ernst advised. "It's better to be safe than sorry."
Lewis said some people with flu symptoms may even have to isolate themselves as a "presumptive COVID case."
Ernst drew parallels to what she imagines may happen with flu season this year to the Ebola epidemic in West Africa.
"We've learned this with Ebola believe it or not," she explained. "We used to have a lot of people coming from West Africa during the Ebola epidemic and they were concerned that they have Ebola."
Doctors discovered that people coming to them with what they thought was Ebola was actually Malaria, which is treatable, because they were not taking their preventative medicine.
"We were going through this whole process where people were really worried and concerned that they had this disease that there's no cure for," Ernst said. "So our message became to anyone that was traveling back and fourth from that area to make sure that you take your anti-malarials."
Ernst explained that coronavirus symptoms and flu symptoms are almost identical, but the incubation period sets the two illnesses apart. The flu is able to incubate in one to four days, while the coronavirus can require up to 14 days of incubation. And if a person does not isolate after being exposed to the virus, that individual could risk spreading the virus to others throughout the entire 14-day incubation period.
Along with the standard coronavirus symptoms such as a cough and a fever, which Ernst said "really mock the flu," many coronavirus patients have been coming to their doctors and telling them that they have an "incredible" sense of fatigue -- something that sets the virus apart from influenza. If a someone begins to lose their sense of smell or taste, the CDC says it is a tell-tale sign that the illness is more likely to be the coronavirus.
In addition, the shortness of breath that often comes on with the coronavirus can be so extreme that it separates itself from the flu.
"Most people with the flu have a fever and the chills and things like that, but they don't have this shortness of breath, this sense that 'I can't get a good air exchange,'" Ernst said.
People that are older, Ernst said, are significantly more likely to experience the intense shortness of breath that comes on with COVID-19 than younger people.
It is important to establish if you have come down with a case of the flu or if you have the coronavirus, not only for quarantine procedures but for treatment as well.
There are many different treatments being used for the coronavirus currently, but Ernst said the treatment patients are prescribed is largely based on the severity of their condition. People who come down with a case of the flu can simply buy some over-the-counter medication, such as Theraflu.
With the coronavirus, there are no over-the-counter medications that a person can take to lessen the symptoms. And the prescription therapeutics that drug companies have in development are at various stages of testing. Regeneron recently announced that it would no longer enroll patients with severe cases of COVID-19 in its experimental antibody treatments, according to Reuters. Around the end of October, remdesivir was given emergency approval in the U.S. for patients 12 years and older in cases of hospitalization.
While asymptomatic individuals have become what Ernst described as "a great fear" with the coronavirus pandemic, the CDC says that individuals can have asymptomatic cases of the flu as well. Following the steps to protect yourself from asymptomatic individuals with the coronavirus, such as hand hygiene and masking, will also help to protect against the flu.
While both the flu and the coronavirus can take a toll on a person's health, Lewis says a winter surge of both illnesses at the same time could lead to another strain on medical facilities as well, especially as hospital staff members become infected themselves.
"It doesn't matter if you have a ventilator if you have no one to administer it," he said. "I think we are going to run into some challenges this season when the two start interacting -- if the flu does start taking off."
He said he has seen a few anecdotal cases where patients actually become infected with both illnesses; however, those cases did not end up becoming any worse than either illness on its own would have been. He believes that duel infections will be "a somewhat rare event" through the season.
"I don't think that there's any evidence to date that shows some sort of really extreme morbidity or mortality that comes out of that combination," Lewis said.
Despite concerns from some that the flu shot is not always effective, Ernst said there is still value in being vaccinated even if you end up getting the flu anyway.
"This happened to my son one year," she said. "It was so much less severe than his friends who hadn't gotten the flu shot. Where he was sick for maybe a day, they were sick for a week."
Ernst said she believes this year there will be an added emphasis from experts on the need to get a flu shot, and that there is also more availability this year than previous years, with even more drug stores offering flu shots than in previous years. She said if someone has toyed with the idea of getting a flu shot in the past, "This is the year to get it."
In October, a study that has yet to be peer-reviewed suggested that a flu shot may even be able to reduce the chance of coronavirus infection; however, it received mixed responses from experts. Lewis had not seen the study himself, but said the flu shot is very specifically formulated for the flu itself and the flu and coronavirus have very different structures, so he thinks there is no reason to suspect carryover protection.
Ellen Foxman, an immunobiologist and clinical pathologist at the Yale School of Medicine, told Scientific American that the study does not provide "definitive evidence" and said there could be other factors at play. She argued that a person who makes the effort to get a flu shot may be more careful about contracting COVID-19 than a person who does not, resulting in fewer chances for infection.
"The main benefit [of a flu vaccine] would be that you have less people that are mildly ill with influenza. Then, if they did get COVID, they are in a healthier and stronger position," Lewis explained. "But I don't think the actual immune response will carry over."
The CDC recommends getting a flu shot in late October; however, it is not too late to get one this year. The CDC says flu shots should continue to be offered throughout flu season, into January or even later. The vaccination takes up to two weeks to begin working in the body, so it is better to get vaccinated before any community outbreaks begin.
"Getting that flu shot, masking, social distancing, hand hygiene -- those are really important things to stop the spread of both the flu and COVID," Ernst said.
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