Cold and flu won't attack you simultaneously, study says
Posted December 16, 2019 3:11 p.m. EST
CNN — Coughing, sneezing and suffering from an achy breaky body? While having the flu is the worst, here's a bit of good news you can take to bed with you: You won't suffer from a cold simultaneously.
That's the conclusion of a new study that analyzed viral test results of more than 44,000 patients in Glasgow, Scotland, between 2005 and 2013. The study was published Monday in the journal for the Proceedings of the National Academy of Sciences.
"It was clear that flu and rhinovirus -- which causes the common cold -- interact in a negative way," said study author Dr. Pablo Murcia of the University of Glasgow Centre for Virus Research. "When there is a lot of flu in the population, there is little rhinovirus, and vice versa."
The finding might explain why colds and flu tend to have different seasonal peaks, which are repeated statistically each year, said lead author Sema Nickbakhsh, a postdoctoral research associate at Glasgow University's Centre for Virus Research.
"The cold virus declines at the time that flu peaks each winter, and that happens every single year," Nickbakhshs said, adding that cold viruses tend to peak in the spring and autumn when flu declines.
Each person in the study was tested for 11 different cold and flu viruses, thus allowing researchers to show the association occurred on both an individual "host" level and the broader population level as well.
"It's very interesting if true," said Dr. William Schaffner, a professor in Vanderbilt University's Division of Infectious Diseases.
"I think what they're saying is virus number one initiates an inflammatory response which then acts as a barrier to the second virus," Schaffner said. "I think there are also some data to suggest that's two viruses cannot simultaneously infect the same cell."
Viruses are parasites that must infect an individual's cells in order to replicate and be maintained in the environment. Some affect a broad number of cells within humans (and animals), and some have predilections for certain parts of the body.
The polio virus, for example, tends to like intestinal cells because they are more receptive to invasion. Bronchitis and pneumonia find it easier to infect the lower respiratory areas of the lung. Influenza and cold viruses are drawn to the cells in the upper respiratory track, such as the nose and throat, which make them particularly easy to spread.
Therefore, it would be possible to have simultaneous viral infections, Schaffner said, but only one virus takes hold to the extent that it triggers our immune system's killer instinct.
"There are times when one viral infection may be so apparent, shall we say, that it actually acts as a barrier to your getting a second," Schaffner said. "We're just beginning to find out whether this is virus specific or whether it has more to do with the intensity of the infection."
Interestingly, a person can become a carrier for a virus without being sick themselves, he explained, which can lead to some disturbing, but common, scenarios.
"I come down with a cold and I say to myself, 'Oh my goodness, how did I get this cold?' I wasn't around anyone who was coughing and sneezing in the last 48 hours," Schaffner said. "But I was around a healthy person carrying the cold virus in their throat who didn't know they were capable of spreading it."
More research needed
The Glasgow study found a number of virus that had both negative and positive impacts on each other, but only at the broader population level. Why that occurs isn't clear.
"They might have the same seasonal preferences or climate and temperature conditions that they favor," Nickbakhsh said. "Or it might be that the two don't occur together because if you're sick and at home or you're in hospital, then you're not going to be exposed to other viruses."
Cooperative relationships have long been known to exist between viruses and bacteria; Flu enhances a person's susceptibility to pneumococcal bacteria, for example.
"So it is well known in the respiratory system that cooperative relationships can occur among pathogens," Nickbakhsh said. "We don't know among the viruses what the reason is for it at this stage, which means a lot more research needs to happen."