Science Monday: Can We Get a Cold + the Flu at the Same Time?
Flu shots to stave off the flu. Hot soup to battle colds. Can we catch both these winter illnesses at the same time?
As a Minnesota native, nothing screams “winter” to me like hours of shoveling snow, cars skidding on ice — and sneezing. I never went anywhere without at least one pocket stuffed full of tissues, shedding and slowly becoming a gigantic, merged wad that I’d pull out to stem the perpetually runny nose.
It seemed like, every year, the common cold (which can be caused by one of several different viruses, although most commonly the rhinovirus) would make the rounds. School probably didn’t help; once one child has a cold, it spread throughout the school faster than a salacious rumor.
The colds also seemed to pop up around the time when flu shots became available, prompting many people, upon hearing a sneeze, to sympathetically ask “Cold or flu?”.
The answer, usually, was a bleary, red-eyed shrug.
Indeed, the two seem pretty similar; they both come up in winter, they both hit us pretty much every year, and they both include many of the same symptoms (sneezing, aching, chills, and congestion). There are some ways to tell the difference, if you pay attention.
But this got me thinking. Why do we either get a cold, or the influenza infection?
Why doesn’t any poor soul come down with both (and probably end up blowing Jabba the Hutt sized boogers out of their nose)?
What is a Cold? What is the Flu?
Even though colds and flus have similar symptoms and strike at similar times, they have different root causes.
Both the common cold and the flu are caused by a virus — a tiny little package of DNA, inside a protein casing. Viruses don’t have the necessary machinery to reproduce on their own; they can only make more copies of themselves by finding a cell, injecting it with their DNA, and hijacking that cell’s machinery in order to make more viruses, instead of performing that cell’s normal functions.
Similarly, both of these illnesses target the respiratory system: the mouth, nose, throat, and lungs.
It’s the specific species of virus that indicates the difference between the cold and the flu — that and the symptoms.
The flu is caused by one specific type of virus, called the influenza virus. A cold, on the other hand, can be caused by one of several different types of virus, including the rhinovirus, adenovirus, or coronavirus.
(Yes, coronavirus! The term “coronavirus” is just the term for a family of viruses that have a “corona” of sugar and proteins surrounding the inner genetic material. The coronavirus in the news, from Wuhan, China, is a specific variant in the coronavirus family.)
It seems like the type of virus that infects us shouldn’t make a difference. Both are hijacking our cells! Why does it matter which type it is?
It turns out that it matters more when we get to symptoms. In general, the symptoms of a common cold tend to be both milder, and last for a shorter period of time, compared to the flu.
A cold will present:
- runny nose
- congestion (mucus buildup)
- sore throat
The typical cold will last a few days to a week and a half.
The flu, on the other hand, will present:
- runny nose and sore throat, same as a cold, but also:
- fever and chills
- vomiting and/or nausea
- in severe cases, pneumonia (fluid buildup in the lungs)
A cold is highly unlikely to cause lasting damage (although in rare cases, it can also lead to pneumonia). The flu, on the other hand, kills as many as 80,000 Americans per year, mostly infants, children, and the elderly. It does so either by triggering inflammation in the lungs, swelling that prevents us from breathing, or by getting into the bloodstream and causing inflammation in other vital organs, such as the heart or brain.
Can I Get Them Both At The Same Time?
Thankfully, it’s extremely rare to develop the cold and the flu at the same time. In a paper published last year, researchers swabbed more than 40,000 individuals, testing for the presence of various viruses.
Interestingly, they found that the cold and flu viruses exhibit a negative correlation, at both the individual and the population level. The flu seems to supplant the territory that was previously held by colds; when flu cases spike during winter months, the number of colds decreases. When an individual gets infected with the flu, they’re up to 70 percent less likely to develop a cold at the same time.
Why’s this happen? It’s still not completely clear, but it seems that, when someone is infected with one virus, it triggers the immune system to go on high alert. This means that, if another virus happens to attempt to strike, the immune system is already primed and poised to drive it off.
Another possibility is that, because the viruses are competing over the same resources and real estate in the respiratory system, the presence of one means that there are fewer resources available for the other to seize. One virus, essentially, starves out another.
Finally, what happens when people get sick? They usually stay home to rest and recuperate — which means that they have a lower risk of being exposed to other people who could be carrying a different virus. If someone stays home with the flu, they’re less likely to be exposed to a virus responsible for the cold.
The cold and the flu can have similar symptoms, but it’s possible to tell them apart; the flu tends to have worse symptoms, and can include more dangerous outcomes, such as vomiting, nausea, diarrhea, and even life-threatening inflammation of the lungs, heart, brain, or other organs.
Even though they’re both caused by viruses, there are different viruses responsible; the influenza virus causes the flu, while the cold can be due to either the rhinovirus, coronavirus, or adenovirus.
Fortunately, it’s very unlikely that you’ll develop both of these viral infections at the same time! Whether it’s due to competition for real estate inside the host body, a heightened immune system ready for a response, or simple lack of exposure, catching one virus seems to help you fight off other infections.
It’s probably not worth catching a cold just to reduce the chance of getting the flu (it’s much simpler to get a flu shot instead), but this may be the basis for new therapies in the future.
Sam Westreich holds his PhD in genetics, focusing on methods for studying the gut-associated microbiome. He currently works at a bioinformatics-focused startup in Silicon Valley. Follow on Medium, or on Twitter at @swestreich.
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