To make the vaccine, the virus is first injected into a chicken egg—and this forces it to mutate and change in order to survive and grow. By the time it's extracted and put into the vaccine, it bears little resemblance to the virus that's in the 'real world', say scientists from the Scripps Research Institute.

It's been the standard way the vaccine has been produced for more than 70 years—which means that, for all those years, the vaccine has been rendered largely ineffective even before it reaches the doctor's surgery. The researchers reckon that, at best, the vaccine is just 33 per cent effective.

For their experiment, the researchers examined the H3N2 influenza virus as it went through the vaccine-making process. The virus is one of the most prevalent, and is one of the most common causes of seasonal flu.

But once it was put into the egg, it started to mutate to adapt to its new environment, and this alteration happened in the part of the virus that is recognised by our immune system.

It's critical that manufacturers start looking at alternative ways to make the vaccines, and especially the flu shots, said lead researcher Nicholas Wu.