They are similar and are sometimes used interchangeably (by people who don’t pay close attention to slight differences of meaning. Here is one significant difference: Something can be important without being vital or essential. Vital or essential implies that, without that vital or essential thing, something becomes impossible. Example: Seatbelts are important in a car, but they are not essential or vital. You can still use the car without seatbelts. But gasoline is essential; without gasoline, you can’t use the car at all.