Flu might protect you from the common cold: Study

Researchers have found that people who suffered from influenza were 70 percent less likely to have acquired rhinoviruses, or the common cold. For the study, published in the journal Proceedings of the National Academy of Sciences, samples from 44,230 cases of acute respiratory illness, in 36,157 patients, were tested for 11 types of respiratory viruses over nine years at National Academy of Sciences (NHS) Greater Glasgow and Clyde board in UK.

"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," said study researcher Sema Nickbakhsh from the University of Glasgow.

During the study, the most striking interaction they found was between influenza A viruses and rhinoviruses, a type of virus that can cause the common cold.

Computer modelling of the data found that the inhibitory interactions between influenza and rhinoviruses appeared to occur within individual people as well as at a population level.

According to the study, patients with influenza were approximately 70 percent less likely to also be infected with rhinovirus, than were patients infected with the other virus types.

"We believe respiratory viruses may be competing for resources in the respiratory tract. There are various possibilities we're investigating, such as these viruses are competing for cells to infect in the body, or the immune response to one virus makes it harder for another unrelated virus to infect the same person," Nickbakhsh said.

Limitations of the study include that the correlations observed cannot show what is causing these interactions and that samples were only taken from people with symptoms of a respiratory infection, so it may not capture how the viruses behave in people who don't develop symptoms.

"A key thing to note with this research is that we're looking at average risks over a very large number of patients who have sought healthcare - that's not to say that occasionally unlucky individuals can't be infected with influenza and a cold virus at the same time," Nickbakhsh said.

The study looked at how 11 viruses interacted. It did find relationships between some of the other virus pairs, but these were not consistent at both the individual host and population level, which the study did find for influenza A and rhinovirus.

"Traditionally, people have studied viruses in isolation - you study only flu or rhinovirus - but we've shown here that we need to also be studying these viruses together like it's an ecosystem," said study lead researcher Pablo Murcia.