What factors might influence how effective a vaccine is when it’s widely released?

A vaccine basically works by injecting a small amount of a virus into your body, and your body learns to fight the virus and becomes immune to the virus.

Explanation:

If it is 100% safe and effective, I will take the vaccine. The vaccine is stored at 2-8 degrees celcius. It can stay in the refrigerator for 72 countinuous hours.  172 countries are working on a vaccine. 5 are the US, China, Brazil, Italy, and Japan. The name of the vaccine is COVAX. Two doses are required, and it should be mandatory for high risk people as well as everyone else.

answer; a muscle cell, another neuron and a of the above

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.