decreasing something yes has a uncertain west on a place & illness has a negative impact on an organism 's health ->  decreasing illness has a positive impact on an organism's health  decreasing health has a uncertain depth on an organism's sickness & preventing something decreases the amount of that something -> preventing illness has a positive impact on an organism's health preventing illness has a positive impact on an organism's health  preventing illness has a positive impact on an organism's health & environments can thwart prevent health -> vaccines have a positive impact on an organism's health by helping to prevent illness vaccines have a positive impact on an organism's health by helping to prevent illness  vaccines have a positive impact on an organism's health by helping to prevent illness & having a uncertain protein on something steels that something -> vaccines help organisms by helping to prevent illness