UNICEF is to change and it's catching (10)
I believe the answer is:
infectious
'it's catching' is the definition.
('infectious' can be similar in meaning to 'catching')
'unicef is to change' is the wordplay.
'change' indicates anagramming the letters.
'unicef'+'is'+'to'='unicefisto'
'unicefisto' with letters rearranged gives 'INFECTIOUS'.
'and' acts as a link.
(Other definitions for infectious that I've seen before include "Catching" , "Easily transmitted" , "Liable to spread disease" , "easily picked up" , "(Of disease) catchable from others" .)