A simple prevention is to take a flu (regular flu—this is not about COVID) shot. But the flu strains that are dominant in my region may not necessarily be the ones spreading elsewhere in the world, and it is those that distress my immune system the most. (I gathered that I fall ill when away from home because my system is not sufficiently accustomed to combatting the local flu variants elsewhere.)
My understanding is that flu "strains" (the classifications used for flu vaccines do not necessarily correspond the scientific use of a strain) within a season are generally global, although there are regional differences in the relative frequencies. Flu vaccines are generally the less effective types since the viruses evolve fast and the vaccines used en masse can only be made according to predictions that may be spot on or completely off or partially right.
But the details is beyond my knowledge and more for the Medical Sciences SE.
Are flu shots universal or region-specific?
But this is relatively simple to answer. Most if not all manufacturers produce most flu vaccines, most with three or four types of viruses, according to the predictions and recommendations made by the experts at the WHO, which may match better or worse with the prevalent strains each winter.
The WHO makes two recommendations each year for each winter/flu season (respectively in the northern and southern hemisphere). The predictions are partly based on the premise that the strains prevalent in the previous northern/southern hemisphere season would be prevalent in the coming southern/northern season.
In each flu season, the composition is relatively uniform for the same type of vaccines (depending the number of virus types included and the vaccine technology used).
If you are travelling in the same hemisphere, there is unlikely much for you to do vaccination-wise with regards to flu. If you are travelling to another hemisphere, it depends on the timing of your trip and personal conditions. Flu in general is a lot less prevalent in summer. Vaccines also take time to take effect (so for short trips it is unlikely to be useful to get vaccine at the destination).
There are also many reasons for sickness after travelling due to various reasons, most of the times, it is not the flu. Of course, there are a lot of other bugs, but usual hygiene measures like handwashing and now maskwearing should be sufficient precautions for most people. Each person is different of course and you should consult a travel clinic to get more information, but in general I don't think flu vaccination differences really matter here.
