Transmissible by direct or indirect contact with an infected person. Contagious diseases may be spread by direct or indirect contact.
An ailment such as food poisoning is infectious, it is capable of producing infection, but it is not contagious. The coronavirus, on the other hand, is both contagious and infectious. Anything that is contagious is automatically also infectious, but the reverse is not true. Both words are frequently used in a figurative manner.