Hi,
I used to be in the medical field before so just to share my point of view here.
I had taken a flu jab last year before my trip to US where the winter is very cold and could have a high potential of catching the flu virus.
Just to claify a bit, there was a shortage of flu jabs in US last year because of contamination with of the flu jabs vaccine. Priority are given to the elderly and young whereby their immune is weaker.
Taking a flu jab does not gurantee that you will not get the virus, it just provide more immunity if your antibodies is strong.
Keep yourself healthy and practise good hygiene will further reduce the risk.