(CNN) The Centers for Disease Control and Prevention recommended the US Customs and Border Protection (CBP) vaccinate migrants in detention against the flu last winter, but CBP rejected the idea, according to a letter obtained by CNN.

The recommendations, first reported by The Washington Post , came from a letter CDC director Dr. Robert R. Redfield wrote in response to US Rep. Rosa L. DeLauro of Connecticut. In the initial October 4 letter, DeLauro asked if CBP spoke with the CDC about the child deaths at detention centers, if CBP asked for guidance about vaccination of migrants and if the CDC has spoken with HHS or the White House about CBP vaccination issues.

Redfield responded to her letter November 7, saying the CDC has been discussing the issue of child deaths with CBP since the beginning of 2018. He also wrote the CDC provided written recommendations to the Department of Homeland Security in January 2019 and, beginning in late May through July 4, the CDC spoke with CBP weekly about the flu cases in migrant facilities.

In the 2018-2019 flu season, at least three children died of the flu while in CBP custody.

DeLauro told The Post CBP's continuing refusal to provide flu vaccines was "unconscionable."

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