Vaccines

Some people believe that vaccines are not effective. Is this true?

This idea comes from the fact that when an outbreak of a preventable disease occurs, of the people who get the disease, more have been vaccinated than have not. This is true even when the vaccine for the disease is 98% effective. This does not mean that the vaccine does not work. This apparent paradox can be explained by understanding two facts about vaccinations in the U.S.: (1) for certain diseases, those who have been vaccinated greatly outnumber those who have not and (2) no vaccine is 100% effective.

During an outbreak of a disease, two groups of people will get the disease. The first group consists of the unvaccinated, and in the U.S. (for certain diseases), this group is very small (often under 1%). The second group consists of those who have been vaccinated but for some reason did not develop an immunity and are therefore not protected. (Most childhood vaccines are effective for 85% to 95% of recipients.) Even when a vaccine is very effective—98%—this second group is still larger than the first group. That means that when there’s an outbreak of a disease, of the affected people, the vaccinated-but-unprotected group will outnumber the unvaccinated group. So, it is misleading to imply that, because the larger group was indeed vaccinated but still got sick, the vaccine did not work. It didn’t work for them, but it did work for almost everyone. Ironically, if immunization efforts were not so successful in the U.S., the apparent paradox would not exist, because the unvaccinated group would be larger, and, during an outbreak of disease, a higher percentage of the total number of affected people would come from that group.