The study by the Francis Crick Institute said that antibiotics damage the body’s early-defence mechanism in the gut, leading to “significantly worse” infections.
Doctors fear overprescribing will create mutant infections that are able to resist all drugs.
The research found that 80 per cent of mice with healthy gut bacteria survived when infected with the flu virus. However, this plummeted to a 30 per cent survival rate in those mice given antibiotics prior to being infected.
Dr Andreas Wack, who led the research, said: “Antibiotics can wipe out early flu resistance. Inappropriate use not only promotes antibiotic resistance and kills helpful gut bacteria but may also leave us more vulnerable to viruses.”
He said that GPs should continue to prescribe antibiotics to patients diagnosed with flu where there was need to treat bacterial infection but warned against people “pre-loading” with antibiotics in the mistaken belief this would protect against catching an infection.