Why would someone not want a vacination? They may have a compromised immune system or be subject to certain skin conditions such as psoriasis or eccema which can cause complications. However, if enough people are vaccinated there is a certain herd immunity that would prevent the spread of the disease. The down side is we may expect one death for every 1,000,000 vaccinations. 300 million vaccinations would mean roughly 200 dead people. IT is a cost benefit thing and I honestly do not know enough to evaluate the risk of not starting to vaccinate the entir populace.
Stay well - Stay safe - Stay armed - Yorktown
I'm guessing like polio a small fraction of a percentage would be susceptible to catching the full blown version.