A teenager attacked a care home worker before spitting on her face and telling her: "You have got corona."
Two youths on bikes approached the woman walking in Sherborn open space in Canford Heath, Poole, on Friday.
Dorset Police said one teenager hit the woman on the head, knocked her to the ground and kicked her multiple times, before spitting on her.
The force said it was "truly despicable" and the victim believed she was targeted because of her uniform.
The teenager who attacked the woman at around 13:00 GMT is described as aged between 16 and 18, with pale skin and possibly light brown hair.
He was wearing a grey tracksuit with the hood up and had a blue bag. He was riding a blue bike.
The second boy told the other to stop, police said.
Police community support investigator Chris Hardy said: "We are committed to supporting those who are helping our communities at this difficult time.
"We are determined to identify those involved and are carrying out a detailed investigation into the incident."