Some of those people are scared but grit their teeth, accept that their chances are better with the medicine, and get on with it.

A few are pushed over the edge and become delusional, believing that imaginary enemies - experts, officials, even human monsters - are out to get them.

"When people are vaccinated against a disease, they usually do not get the disease or get only a mild form of the disease. However, because no vaccine is 100% effective, some people who have been vaccinated still may get the disease." https://www.merckmanuals.com/en-ca/home/infections/immunization/overview-of-immunization

"Fifty years ago, when an estimated 2 million or more cases of whooping cough with 7,000 deaths occurred annually in the United States, little attention was paid to the rare infant who displayed severe symptoms following inoculation with the newly developed vaccine." https://www.ncbi.nlm.nih.gov/books/NBK216824/)

Some foreign countries prey on those people, feeding their fears, in an effort to disrupt society: https://en.wikipedia.org/wiki/Internet_Research_Agency