any vaccine effectiveness can vary, recent studies show that flu vaccination reduces the risk of flu illness by between 40% and 60% among the overall population during seasons when most circulating flu viruses are well matched to the flu vaccine.
Explanation:
this is right i had to to a test and a whole lesson over this. ^^^^ that all is from my notes!
The population would increase drastically and we would run out of resources for food. then the birth rates would eventually equal out to number of death rates . we then wouldnt have anyone alive
