In the face of a nationwide outbreak of hepatitis A virus (HAV), health and prison officials in St. Louis, Missouri, are teaming up to vaccinate more than 800 prisoners against the virus, St. Louis Public Radio reports.

Over the next few weeks, the St. Louis Department of Health and St. Louis Division of Corrections will provide vaccines to all eligible inmates in the city’s two jails. About 1,000 people are housed at both facilities. The mass vaccination is intended to be a one-time event.

Vaccinating inmates, health officials explain, is essential because prisoners are one of the most at-risk groups for hepatitis A in the country—along with people experiencing homelessness, intravenous drug users and other people who live in unsanitary environments. Vaccinating inmates also helps protect jail employees and visitors, say prison officials, as well as the general public, since populations in city jails are often in flux and viruses can spread within and outside the facilities.

St. Louis appears to be getting ahead of the outbreak. Missouri has reported 378 cases of hepatitis A since September 2017, but only one case has been recorded in St. Louis so far, and no cases have been reported at either of the city’s two jails. This sort of preemptive effort is one many hepatitis advocates have pushed for since the start of the outbreak.

City corrections and health officials say they will also give inmates who are released after a single dose the second required dose to ensure full protection. 

To learn more about hepatitis in prisons, click here.