The flu and the common cold are two classic winter infections. However, researchers have discovered that it is almost impossible to catch both at the same time. The two viruses compete with each other.
By the end of November, millions of Americans have been vaccinated against the flu. The flu is one of the most common respiratory infections in winter, along with the common cold. Both diseases are caused by two families of viruses: rhinoviruses (colds) and flu viruses (influenza). If you have a good chance of getting one of these two illnesses this winter, you cannot get both at the same time. The viruses infect the same cells of the respiratory mucosa, but they compete with each other and inhibit each other.
More than 40,000 people with a respiratory infection have been studied statistically by researchers at the University of Glasgow (Scotland). While 35% of them were infected with one of the eleven types of respiratory virus tested, only 8% were infected with two or more viruses at the same time. The results of this study are published in the journal Pnas.
The virus fights the arrival of the other
“One really striking pattern in our data is the decline in cases of the respiratory virus rhinovirus, which is typically a mild common cold causing virus, occurring during winter, around the time that flu activity increases.” says Dr. Sema Nickbakhsh, lead author of the study. According to him and his team, innate immunity arises when the flu virus attacks cells in the respiratory tract. A veritable army of interferons – proteins that act on the immune system – comes into play to counteract the viral infection. If a rhinovirus were to pass through and attempt to infect the cells, it would be destroyed by these interferons. This process also works in reverse when a person is already infected with the cold virus.
Improving prediction of seasonal illness
These results also suggest that the incidence of influenza infections is not only related to season, age, or health of the individual, but also to the incidence of other viral infections. Thus, a better understanding of the interactions between viruses could improve, for example, seasonal forecasts and improve strategies to combat these winter diseases.