vacuna

In a sentence

• La vacuna contra la grip es recomana cada any.

  The flu vaccine is recommended every year.

  Here, 'vacuna' is used as a noun referring to the medical substance designed to trigger immunity against a disease (the flu in this case).

• Vacuna el teu gos per evitar la ràbia.

  Vaccinate your dog to prevent rabies.

  In this sentence, 'vacuna' is the imperative form of the verb 'vacunar', used to instruct someone to administer a vaccine to prevent illness (rabies here).

• L'últim assaig clínic ha provat una nova vacuna.

  The latest clinical trial tested a new vaccine.

  Here, 'vacuna' appears again as a noun, referring generically to a newly developed immunization product within the context of clinical testing.