New York, Sep 5 (IANS): Rhinovirus, the most frequent cause of common cold is capable of preventing the flu virus from infecting airways by jump-starting the body's immune defences, say researchers.

The findings, published in the journal The Lancet Microbe, help answer a mystery surrounding the 2009 H1N1 swine flu pandemic.

For the study, the research team studied three years of clinical data from more than 13,000 patients at Yale-New Haven Hospital in the US with symptoms of respiratory infection.

The researchers found that even during months when both viruses were active if the common cold virus was present, the flu virus was not.

"When we looked at the data, it became clear that very few people had both viruses at the same time," said study senior author Ellen Foxman from the Yale University in the US.

Foxman stressed that scientists do not know whether the annual seasonal spread of the common cold virus will have a similar impact on infection rates of those exposed to the coronavirus that causes Covid-19.

"It is impossible to predict how two viruses will interact without doing the research," she said.

To test how the rhinovirus and the influenza virus interact, Foxman's lab-created human airway tissue from stem cells that give rise to epithelial cells, which line the airways of the lung and are a chief target of respiratory viruses.

They found that after the tissue had been exposed to rhinovirus, the influenza virus was unable to infect the tissue."The antiviral defences were already turned on before the flu virus arrived," she said.

The presence of rhinovirus triggered production of the antiviral agent interferon, which is part of the early immune system response to the invasion of pathogens.

"The effect lasted for at least five days," Foxman said.

The researchers said that their lab has begun to study whether the introduction of the cold virus before infection by the Covid-19 virus offers a similar type of protection.