I'm pretty certain that any airline has zero liability for contagion on board. There's no way to guarantee that you won't get a bug when flying with them. There's only a way to guarantee that measures are in place to ensure as sanitary an environment as practically possible. Once you're familiar with that and have made the decision to travel either at your own risk or under an appropriate insurance cover, suing MOL would be about as productive as suing TfL after getting a bug on the tube.