Studies on immune responses in afferent and efferent lymph of lymph nodes draining the tissues have contributed to the concept that primary immune responses are generated in the lymph nodes with a delay before antigen-specific effector cells arrive at the affected tissue.
Lightning strikes the ground approximately 25 million times each year in the U.S. According to the NWS, the chance of an individual in the U.S. being killed or injured during a given year is one in 240,000. Assuming an average life-span of 80 years, a person's odds over their lifetime becomes one in 3000.
Shark attacks are extremely rare. An individual is three times more likely to be hit by lightning than to be bitten by a shark. There were an average of 32 shark attacks per year in U.S. waters between 1990 and 2004. Of the 490 attacks during this 15-year span, 11 were fatal. Most people die in the deep waters, some on the shores.