Few, but can occur. Zenapax is the brand name of the il2 receptor blocking antibody called daclizumab. It is a humanized monoclonal antibody most often used to prevent rejection of organ transplants. Any antibody (protein) can cause infusion reactions such as fever, chills, joint pains, headache, sob, etc. It was taken off the market in the us by its manufacturer in 2010. For poor sales, not safety issues.