Maintaining/improving stomach acid levels may help along with taking probiotics as allegedly this is where your first line of defence is against infection. I have found in the years when I have been organised enough to take echinacea in winter I have had fewer and easier colds. I'll definitely try and remember to take it this year!
So if that was the case then, can you trick your immune system into doing its thing at a more convenient time so these disappointments don't occur? Say, some complete rest a couple of weeks before the expensive annual holiday. I too regularly have bouts of cold/flu on holiday - we were skiing in Finland once and I was burning up so I stayed in bed in the hotel with the patio doors wide open - it was -26C outside and I was still sweating buckets!
Could it be that the immune system holds off fighting illness (viruses and the likes) whilst you are working hard (running or jobwise) and when it feels you ease off a bit (whilst tapering or starting your holiday) takes the opportunity to do its job? Just a theory, could be total bo**ocks...
I also feel that too many people resort to swearing... I want to promote the campaign for more picturesque speech.
Jenny - what's so terrible about swearing? Swear words are just that - words - I'm pretty sure there are many non-swear words that could cause offence. There are times when a good swear really does help!