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This is one of the 117 mis-spellings listed as 'Common difficulties' in the section on 'Spelling' within 'Writing' in UEfAP.

The verb 'to vaccinate', with the associated nouns vaccine, vaccination and vaccinator, etc, have two '-c-'s. Each '-c-' represents a separate consonant in English, a '-k-' and an '-s-', to produce 'VAK-seen', IPA: /ˈvæk siːn/ etc.

They all derive from the Latin vacca 'a cow', because the first widely publicized successful vaccination in Europe was in 1796, when Edward Jenner (1749-1823) used the cowpox virus to protect against the related but much more dangerous smallpox. (Some protection had previously been given by variolation, the deliberate infection of a patient with a dried, and thus less potent, material from blisters of smallpox itself. Historians of eighteenth century medicine should be careful to distinguish between vaccination and variolation (which had been developed in China around 1,000 CE): the two terms were not carefully distinguished by contemporaries.)
Spelling confusion may be caused by inoculate, inoculation etc, 
words which have, in general use, very similar meanings - but written with only one '-c-'. (They are derived from Latin oculus, 'eye'.)