Active and Passive Immunity. Naturally acquired active immunity occurs when the person is exposed to a live pathogen, develops the disease, and becomes immune as a result of the primary immune response. Artificially acquired active immunity can be induced by a vaccine, a substance that contains the antigen.
Lower back tightness can cause muscle twitching, pain and reduced range of motion. Lower back muscle tightness is the cause of a muscle spasm. This can be brought on by a strain, overuse or muscle weakness, according to BetterMedicine.com.
After four or five days, providing the inflammation has subsided, applying heat for 15 or 20 minutes at a time may be beneficial. Heat increases blood flow and helps relax tight back muscles. (Pain can cause muscles to tighten or spasm).