New vaccine technology cracked by unknown actress essential to 3 (5)

I believe the answer is:

myrna

I'm a little stuck... Click here to teach me more about this clue!

'new vaccine technology cracked' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'unknown actress essential to 3' is the wordplay.
'unknown actress' becomes 'my' (I can't explain this - if you can you should give a lot more credence to this answer).
'essential to' indicates the central letters.
'3' becomes 'ternary' (synonyms).
The central letters of 'ternary' are 'rna'.
'my'+'rna'='MYRNA'

'by' is the link.

Can you help me to learn more?

I've seen this clue in The Independent.

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