What Causes Lower Back Stiffness?
Not a virus.
Detailed Answer:
I read your question carefully and I understand your concern.
Lower back stiffness is not associated with a viral cause, at least not as the only symptom.
Much more common causes are degenerative changes of the spine with inflammation or a muscle strain. They are managed similarly at this stage. Unless there are other symptoms (like pain or weakness radiating in the limbs, bladder control issues, fever, a traumatic event originating the symptoms) I wouldn't worry, symptoms may persist for a few weeks but should gradually improve.
Over the counter anti-inflammatory medication like Ibuprofen may help. So can muscle relaxants like Flexeril. Warm compresses may also be beneficial.
I remain at your disposal for other questions.