Being exposed to one respiratory virus can help human bodies resist other competing pathogens, revealed scientists, explaining why a potential 'twindemic' of COVID and flu was stopped in its tracks.

Many public health experts had feared that flu and COVID-19 would grip countries this last winter, but it never happened, the New York Times reported. While some individuals may have ended up being infected with two or even three viruses simultaneously, it did not take place at a population level.

Strict measures such as masks, and social distancing, among others, imposed to control the spread of COVID largely prevented flu outbreaks while the Coronavirus reigned, and resurged as it receded. But it was not alone.

In a study published in the Journal of Experimental Medicine, scientists found the reason to be a biological phenomenon, called viral interference. This means that exposure to one respiratory virus may put the body's immune defences on high alert, blocking other pathogens from gaining entry into the airways, the report said.

Using a model of human airway tissue, the team showed that rhinovirus infection stimulates interferons -- first nonspecific defenders in the human body -- that can then fend off the coronavirus.

"My gut feeling, and my feeling based on our recent research, is that viral interference is real," Ellen Foxman, an immunologist at the Yale School of Medicine, was quoted as saying. "I don't think we're going to see the flu and the Coronavirus peak at the same time," Foxman said.

In a separate study, researchers from the University of Sheffield explored the viral interference phenomenon in children. Because it would be unethical to deliberately infect children with the flu, they gave children in the Gambia a vaccine with a weakened strain of the virus, the report said. They found that children who already had high levels of interferon ended up with much less flu virus in their bodies than those with lower levels of interferon.

The findings suggested that previous viral infections primed the children's immune systems to fight the flu virus -- a potential reason why children, who tend to have more respiratory infections than adults, seem less likely to become infected with COVID.

The theory can also be applied to adults. Recent studies have shown that co-infection of flu and Coronavirus are rare, and those with active influenza infection were nearly 60 per cent less likely to test positive for Coronavirus, the report said.