According to the safety communication:
"The U.S. Food and Drug Administration (FDA) is warning parents, caregivers, and health care providers not to use neck floats with babies for water therapy interventions, especially with babies who have developmental delays or special needs, such as spina bifida, spinal muscular atrophy (SMA) type 1, Down syndrome, or cerebral palsy. The use of these products can lead to death or serious injury."
Read the full safety communication: Do Not Use Baby Neck Floats Due to the Risk of Death or Injury: FDA Safety Communication - FDA.gov