What are the differences between H7N9, H1N1 and H5N1 viruses?

All three viruses are influenza A viruses but they are distinct from each other. H7N9 and H5N1 are considered animal influenza viruses that sometimes infect people. H1N1 viruses can be divided into those that normally infect people and those that normally infect animals.

(Source: World Health Organization)