Vaccinia keratitis, although rare (and severe if left untreated), occurs when vaccinia virus is accidentally implanted into the periorbital structures or the cornea. Viral replication and the immune response lead to ulceration with subsequent corneal scarring or clouding. Lesions of the cornea secondary to implantation are potentially threatening to eyesight.

Although individuals with healthy eyes are susceptible to vaccinia keratitis, those with pre-existing eye disease (especially inflammatory diseases of the lids, conjunctiva and cornea) are particularly prone to implantation from contact with contaminated hands. Caregivers who bathe or otherwise handle children with vaccinations are the most likely to experience accidental transfer.

To prevent vaccinia keratitis, avoid vaccinating individuals with inflammatory eye or periorbital disease and instruct vaccinees and close physical contacts (eg, household members) of vaccinees to avoid touching, rubbing or otherwise performing any maneuvers that might transfer vaccinia virus from a vaccination site to the eye or surrounding skin.