"The scientists imagine these types of chips being implanted into the human body, and then wirelessly communicating information on what they measure via ultrasound. In its current form this is limited to body temperature, but other possibilities include blood pressure, glucose levels and respiratory function."
Nobody says it's hidden in the vaccines. But injectable microchips are a thing: https://newatlas.com/electronics/worlds-smallest-single-chip-system-injectable/
"The scientists imagine these types of chips being implanted into the human body, and then wirelessly communicating information on what they measure via ultrasound. In its current form this is limited to body temperature, but other possibilities include blood pressure, glucose levels and respiratory function."
They've been doing this since for a long long time.