Researchers also warned that the drugs’ effects on bacteria in the gut could make the disease more deadly.
Although the scientists’ research examined the results in mice, they stressed the principle could also apply to humans.
The team discovered that when bacteria living in a mouse’s gut detect a virus, they send out a chemical signal. This activates a defensive immune reaction in the lungs.
When mice with healthy gut bacteria were infected with the flu, about 80% of them survived. But only a third remained alive if they were given antibiotics before being infected. Dr Andreas Wack, from the Francis Crick Institute in London, which carried out the study, said: “Gut bacteria send a signal that prevents the virus from multiplying so quickly.