Arthritis (from Greek arthro-, joint + -itis, inflammation) is a group of conditions where there is damage caused to the joints of the body. Arthritis is the leading cause of disability over the age of 65.
There are many forms of arthritis, each of which has a different cause. The form of vaccine-associated is implicated as an autoimmune form in which the body is attacking itself.
Why would the body attack itself? The answer is usually a disruption in immune function. Many vaccine components (ingredients) are know to do this and specific many vaccines have been well-documented to directly and immediately cause arthritic conditions. The onset can also be latent or delayed, so no one knows to what degree vaccines have cause the ever-increasing incidence of autoimmune arthritis.