Producing or capable of producing infection, containing pathogenic agents which may be transmitted. 

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.

» COVID-19 Glossary