For months, the Centers for Disease Control and Prevention (CDC) has recommended U.S. Customs and Border Protection (CBP) to vaccinate immigrants and asylum seekers in detention against the flu virus, but the agency has continued to ignore the medical professionals’ suggestions, the Washington Post reports.

According to a letter from the CDC to Rep. Rosa DeLauro (D-Conn.) dated November 7, the CDC has been writing recommendations about flu prevention to Border Patrol officials since January and had regular calls with the agency on the matter between May and July. During their correspondence, CDC representatives urged CBP to provide flu vaccinations “at the earliest feasible point of entry” for all people who have crossed the border that are older than six months.

In the letter, CDC Director Robert Redfield notes that the agency started making recommendations to CBP after growing concerned about flu-related deaths of children in Border Patrol custody.

Medical professionals have repeatedly stressed concern about the high risk of influenza outbreaks at detention centers. While detention at CBP facilities are supposed to be short term, many immigrants and asylum seekers have stayed for longer periods. Having a combination of long-term detainees with short-term ones particularly puts people at risk for illness.

According to The Hill, during combined CDC visits to Border Patrol facilities, teams examined a total of 65 people. Of them, six tested positive for influenza.

Despite the glaring data, CBP continues to reject proposals for vaccinating immigrants.

“CBP has significantly expanded medical support efforts, and now has more than 250 medical personnel engaged along the Southwest Border. To try and layer a comprehensive vaccinations system on to that would be logistically very challenging,” an agency spokesperson told the political news site.

The agency said they will not vaccinate immigrants because individuals receive this treatment once they are transferred to other agencies, like the Department of Health and Human Services or Immigration and Customs Enforcement.

For CBP, these percussions don’t “make sense from a law enforcement, public health or good governance perspective.”

In the time that the CDC has urged Border Patrol to vaccinate immigrants and asylum seekers, at least two children have died in U.S. custody related to the flu.