Treat vain nurse now and then for preventable bacterial infection (7)
I believe the answer is:
tetanus
'bacterial infection' is the definition.
(I know that tetanus is a type of bacterial infection)
'treat vain nurse now and then' is the wordplay.
'now and then' means one should take alternating letters (letters taken on a regular basis, now and then).
'treat'+'vain'+'nurse'='treatvainnurse'
The alternating letters of 'treatvainnurse' are 'TETANUS'.
'for preventable' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for tetanus that I've seen before include "Locker" , "Attunes to disease from dog-bite" , "Infection from wound" , "Bacterial disease" , "Disease known as lockjaw from rabid dog bite" .)