Zinc is a trace metal that is essential in over 300 enzymes and therefore effects many systems of the body. It is very important in the immune system for helping us have white blood cells that are more tolerant of other cells and proteins - Regulatory T cells that help protect against infection without being so active that seasonal allergies or autoimmune disease aren't problems.
Zinc can also be moved from some types or parts of cells to other areas to protect against different type of infectious pathogens. Some are susceptible to too much zinc and immune cells can overload the pathogen with more zinc and others are susceptible to having too little zinc and then the immune system will remove zinc from being available.
Supplements of zinc given either daily or weekly have been found to help reduce the prevalence or severity of some common childhood illnesses such as diarrhea. Excessive amounts are not beneficial though and may reduce immune and membrane function. Copper and zinc levels also need to be in balance for optimal health. Food sources of both were included in the last post: Trace Metals - it's teamwork, or see The 10 Best Foods for Zinc, (healthline.com).
Reference: Trace Metals and Infectious Diseases, Ed. by Jerome O. Nriagu and Eric P. Skaar, (2015, MIT Press, mitpress) pp 216-222
Disclaimer: Opinions are my own and the information is provided for educational purposes within the guidelines of fair use. While I am a Registered Dietitian this information is not intended to provide individual health guidance. Please see a health professional for individual health care purposes.