She said those with the vulnerability have a overblown immune response.

"Some people will experience more severe symptoms than others when they are acutely sick with the same infection because their body's response is more intense which in turn is due to their genetic make-up," Vollmer-Conna said.

She said: "This group in the population were found to spend twice as many days in bed during the acute illness and they also reported more than twice as many days when they were unable to perform their normal roles and duties."

The findings could ultimately help identify people who are vulnerable and give them individualised prevention and treatment for common infectious diseases, and priority therapy in the event of a pandemic.

"In certain conditions, it may even be possible to save lives," she said.