Explain why global efforts are being made to mass vaccinate populations and the importance of herd immunity in wiping out disease nationally and globally?

If you’re referring to the current Coronavirus pandemics, the reasons we want to mass vaccinate the population is to stop the spread by making it harder to find a host that it can use to replicate. The more times the RNA virus replicates, the more mutations are generated, the more likely a strain, that can escape the any immunity developed, can occur. Herd Immunity is what will help reduce the ability of a virus to spread. If the virus can’t find a host to replicate in (because the host is immune to the virus) the harder it is for the virus to spread.