The flu and the common cold are the two classic winter infections. American researchers have discovered that it is however impossible to catch them at the same time. The two viruses compete with each other.
At the end of November, already a million French people had been vaccinated against the flu. The campaign started on October 15 this year, with a novelty: it is possible to get vaccinated in pharmacy. Flu is one of the most common winter respiratory infections along with the common cold. These two diseases are caused by two families of viruses: rhinoviruses (colds) and influenzas (flu). If you have a high chance of catching one of these two diseases this winter, you cannot catch both at the same time. Viruses infect the same cells of the respiratory mucosa, but they “compete” and inhibit each other.
More than 40,000 people with a respiratory infection were the subject of a statistical study, conducted by researchers from the University of Glasgow (Scotland). If 35% of them were infected by one of the eleven types of respiratory virus analyzed, only 8% were infected by at least two viruses at the same time. The results of this study are published in the journal Pnas.
The virus fights the arrival of the other
The scientific team has found that influenza-type viruses and rhinoviruses in particular are not made to get along. “One of the surprising results of our study is the decrease in cases of infection by rhinoviruses, the causative agent of the common cold, during the epidemic peak of the flu”, explains Dr. Sema Nickbakhsh, lead author of the study. According to him and his team, innate immunity kicks in when the flu virus attacks cells in the airways. A veritable army of interferons — proteins that act on the immune system — is in place to thwart viral infection. If a rhinorivus passed by and tried to infect the cells, it would be destroyed by these interferons. This process also works the other way around, when a person is already infected with the flu virus.
Improve the prediction of seasonal diseases
“We are studying several possible scenarios. Viruses can compete to infect cells in the body or the immune response complicates the infection of another type of virus”, continues Dr Nickbakhsh. These results also suggest that the incidence of influenza infections is not only related to the season, the age or the health of the person, but also to the incidence of other viral infections. So, if virus-virus interactions are better understood, this could improve, for example, seasonal predictions and improve strategies to combat these winter diseases.
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