A childhood illness that does not stay mild
In a young child chickenpox is usually a week of spots and irritability. In an adult it is a different disease: a far heavier rash, high fever, and a meaningful risk of pneumonia, which is the complication that puts adults in hospital.
Because the UK has never had routine childhood varicella vaccination, a proportion of British adults reach their twenties and thirties without immunity - more often those who grew up in smaller households or outside the UK. They tend to find out at the worst possible moment.
Where travel comes into it
The virus is everywhere, so this is not about a destination. It is about consequence. Catching chickenpox in the second week of a six-month posting, or on a cruise, or while looking after children abroad, is a serious disruption as well as a serious illness - and some airlines will not carry an actively infectious passenger.
It is also the vaccine we are asked about most often by people planning a pregnancy, since it cannot be given during one. Getting it done before, rather than finding out you are not immune during, is the straightforward move.
Chickenpox, shingles and the same virus
Chickenpox and shingles are caused by the same virus. After chickenpox it stays dormant in nerve tissue and can reactivate decades later as shingles.
They are not interchangeable vaccines. Varicella vaccine prevents a first infection; the shingles vaccine is a different product for people who have already had chickenpox and want to reduce the chance of reactivation. Our pharmacy colleagues cover shingles vaccination - this page is about the first of the two.