In the Whats App notification options you can choose between “short”, “long” and “normal” vibration. I’ve chosen the “short vibration” mode. However, the vibration is not different to the normal vibration. This is the same for “long vibration”.
The short vibration mode should result in only a single short vibration (such as the short vibration when the Fairphone is rebooted). Since the Fairphone does vibrate shortly when turned on/off, it should not be a hardware problem.