Simply put: Vaccination saves lives.

Few measures in public health can compare with the impact of vaccines. Vaccinations have reduced disease, disability, and death from a variety of infectious diseases. For example, in the United States, children are recommended to be vaccinated against 16 diseases (1). Table 1 highlights the impact in the United States of immunization against nine vaccine-preventable diseases, including smallpox and a complication of one of those diseases, congenital rubella syndrome, showing representative annual numbers of cases in the 20th century compared with 2016 reported cases (2, 3). All of the diseases have been reduced by more than 90% and many have either been eliminated or reductions of 99% or more have been achieved. A recent analysis of vaccines to protect against 13 diseases estimated that for a single birth cohort nearly 20 million cases of diseases were prevented, including over 40,000 deaths (4). In addition to saving the lives of our children, vaccination has resulted in net economic benefits to society amounting to almost $69 billion in the United States alone. A recent economic analysis of 10 vaccines for 94 lowandmiddleincomecountries estimated that an investment of $34billion for the immunization programs resulted in savings of $586 billion in reducing costs of illness and $1.53 trillion when broader economic benefits were included (5). The only human disease ever eradicated, smallpox, was eradicated using a vaccine, and a second, polio, is near eradication, also using vaccines (6, 7). Vaccines not only provide individual protection for those persons who are vaccinated, they can also provide community protection by reducing the spread of disease within a population (Fig. 1). Person-toperson infection is spread when a transmitting case comes in contact with a susceptible person. If the transmitting case only comes in contact with immune individuals, then the infection does not spread beyond the index case and is rapidly controlled within the population. Interestingly, this chain of human-tohuman transmission can be interrupted, even if there is not 100% immunity, because transmitting cases do not have infinite contacts; this is referred to as “herd immunity” or “community protection,” and is an important benefit of vaccination. Mathematical modelers can estimate on average how many persons the typical transmitting case is capable of infecting if all of the contacts were susceptible (i.e., a population of 100% susceptibility). This number is known as R0, or the basic reproductive number. The immunity threshold needed within the population for terminating transmission can be calculated in percent as (R0 − 1)/R0 × 100 and is a guide to setting immunity levels and vaccination coverage targets for various diseases (8). For example, measles is one of the most