Health officials say Nigeria’s meningitis outbreak has killed at least 489 people as of Monday.

Isaac Adewole, Nigeria’s Minister of health says 4,637 meningitis cases have been confirmed. The federal government has kicked off a nationwide vaccination campaign for millions of people, though there is a worldwide shortage for the strain, which inflames the spinal cord and brain.

The northern part of the country have suffered a great deal of the disease outbreak. Zamfara state is the worst hit with 216 deaths. Katsina, Kebbi, Niger and Sokoto states in northwest and north-central Nigeria also have seen cases since the disease surfaced in December.

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Children are mostly victims of the disease.

In 2015 a meningitis epidemic killed 1,100 people and infected more than 10,000 in Nigeria and neighboring Niger. There are fears that this outbreak could again spread across the border.