i don't know him or her but you must know a person before you define your thoughts about him or her
answer: the valid reasons are they may give a little failure effect of the vaccine that may cause us people to have sickness
explanation: some vaccines are dengue vaccine that also been failed to make,some children past away just of oneto two shots of it so this is one valid reason in my guess only
its a branch of science that study about the environment
lithium is an example, after it bonds an element with a 7 valence electrons like fluorine.