Popular vaccine protects juvenile (5)
I believe the answer is:
larva
'juvenile' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'popular vaccine protects' is the wordplay.
'protects' says the answer is hidden in the clue (hidden letters are protected by the clue).
'LARVA' can be found hidden inside 'popular vaccine'.
Can you help me to learn more?
(Other definitions for larva that I've seen before include "Grub of e.g. beetle" , "Immature form of caterpillar" , "Insect just out of egg" , "Insect in the first post-egg stage of its life" , "shows form of immaturity" .)