HOW LONG DOES IT TAKE?

The flu jab to work: Two weeks

THE vaccine doesn’t provide maximum immunity against the flu virus straight away — instead it builds over time, explains Dr Jeremy Rossman, a senior lecturer in virology at the University of Kent.

That’s because the flu vaccination works using a part of the immune system known as the adaptive response — where the body produces antibodies to attack infection. ‘To do this, immune cells called the B-cells have to replicate, and it takes one to two weeks for the cells to replicate enough to provide sufficient antibodies to protect you,’ says Dr Rossman.

This is why, even though the main flu season in the UK runs from October to May, vaccination programmes start in September.