Is the flu caused by shaking hands with infected people, the close proximity of chicken coops, pig-pens, and houses in China, or failure to get flu shots? If causality is a law of nature, why can there be multiple causes of a thing? Does the boy hit the ball, or is the ball hit by the boy? Do you think the fact that we give distinct scientific names to creatures we find constitutes a natural law that prevents them from mating? Like lions and tigers, or camels and llamas, for example?
You can usually think more analytically about how things happen if you just run the numbers--causality is a useful, but neither infallible, nor indispensable mental convenience, in aid of human decision-making, not a law of nature.
Defining the question is critical.
Getting the flu may be caused by a number of things. The flu itself is a result of the interaction of the relevant virus and the infectee.
For instance one may be infected (have the virus setting up housekeeping) but not sick (a killer immune system)
Too many effects or too many causes usually mean a carelessly phrased question.
I am attempting to learn about causeless sub-atomic effects, courtesy of another poster, so on another level you may be right. Maybe I should modify my statement to include only the Newtonian world.