I'm using version 1.21-1.6.1b, Neoforge 1.21.1. I was testing adding some modded items to the Infection Cures and Immunity Item lists, and discovered this. I then started a fresh pack with nothing but The Hordes and Atlas Lib installed just to rule out anything else messing with it. I noticed that anything in the Immunity Items json would not remove the Infection, even if they were included in the Infection Cures json. For example, regular gold apples would successfully remove the Infection (without adding Immunity, as expected), but enchanted golden apples would NOT remove the infection, they would ONLY grant Immunity despite being in both lists by default. After removing the enchanted golden apples from the Immunity Items json, they then successfully cured the infection.

That's weird, applying the immunity effect should automatically remove infection when applied, I'll take a look and see what might be going on.

i made thoses modifications it worked you could try this.
{
"replace": false,
"values": [
"minecraft:golden_apple",
"minecraft:enchanted_golden_apple",
"cure:vaccine"
]
}
in the infections cures files and
[
{
"item": "minecraft:golden_apple" ,

	"duration": 150
	
},
{  
	"item":   "minecraft:enchanted_golden_apple",
    
	"duration": 150
},
{  
	"item":   "cure:vaccine" ,
    
	"duration": 150
}

]
in the immuniti items file