Which of the following is essential until the patient is secured on a backboard?

Manual support of the patient's head is crucial until the patient is secured on a backboard because it helps prevent further spinal injury. When dealing with potential spinal injuries, maintaining head and neck alignment is a priority to minimize movement that could exacerbate the injury. Supporting the head manually ensures that it remains stable and aligned with the spine until the backboard can provide that same level of support.

Other practices such as monitoring vital signs, communication with paramedics, and repositioning the patient are certainly important in a rescue scenario, but they do not take precedence over the immediate need for head and neck stability during extrication. Until the patient is safely immobilized on a backboard, maintaining manual control over the head is vital for patient safety and is the immediate step to protect their condition.