Vaccine is pronounced vak-SEEN (IPA /vækˈsiːn/). Stress 'SEEN' with a long 'ee'; second syllable rhymes with 'seen'.
IPA: /vækˈsiːn/
Syllables: vak · SEEN
Common ESL mistake: Learners say 'VAK-sin' with stress on first and short vowel.
Tip: Stress 'SEEN' with a long 'ee'; second syllable rhymes with 'seen'.