The basic reproduction number (R0), also called the basic reproduction ratio or rate or the basic reproductive rate, is an epidemiologic metric used to describe the contagiousness or transmissibility of infectious agents. R0 is affected by numerous biological, sociobehavioral, and environmental factors that govern pathogen transmission and, therefore, is usually estimated with various types of complex mathematical models, which make R0 easily misrepresented, misinterpreted, and misapplied. R0 is not a biological constant for a pathogen, a rate over time, or a measure of disease severity, and R0 cannot be modified through vaccination campaigns. R0 is rarely measured directly, and modeled R0 values are dependent on model structures and assumptions. Some R0 values reported in the scientific literature are likely obsolete. R0 must be estimated, reported, and applied with great caution because this basic metric is far from simple.

State-mandated vaccination requirements for school entry protect children and communities against vaccine-preventable diseases (1). Each school year, federally funded immunization programs (e.g., states, territories, jurisdictions) collect and report kindergarten vaccination data to CDC. This report describes vaccination coverage estimates in all 50 states and the District of Columbia (DC), and the estimated number of kindergartners with at least one vaccine exemption in 47 states and DC, during the 2015-16 school year. Median vaccination coverage* was 94.6% for 2 doses of measles, mumps and rubella vaccine (MMR); 94.2% for diphtheria, tetanus, and acellular pertussis vaccine (DTaP); and 94.3% for 2 doses of varicella vaccine. MMR coverage increased in 32 states during the last year, and 22 states reported coverage ≥95% (2). A total of 45 states and DC had either a grace period allowing students to attend school before providing documentation of vaccination or provisional enrollment that allows undervaccinated students to attend school while completing a catch-up schedule. Among the 23 states that were able to voluntarily report state-level data on grace period or provisional enrollment to CDC, a median of 2.0% of kindergartners were not documented as completely vaccinated and were attending school within a grace period or were provisionally enrolled. The median percentage of kindergartners with an exemption from one or more vaccinations was 1.9%. State and local immunization programs, in cooperation with schools, can improve vaccination coverage by ensuring that all kindergartners are vaccinated during the grace period or provisional enrollment.

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A total of 95 811 students aged 13-15 years participated in nationally representative Global School-based Student Health Surveys (GSHS) in 47 low-income and middle-income countries conducted between 2003 and 2012. On average, about 40% of the participants in each country reported at least one injury in the past year that was serious enough to cause the student to miss at least one full day of usual activities (such as school, sports and a job) or to require treatment by a healthcare professional. In 40 of the 47 countries, boys reported a significantly higher injury rate than girls. Based on these numbers, injuries likely cause approximately four million days of school absence by lower secondary school students annually. Most of these injuries are preventable.

Effective vaccination policy requires a robust understanding of vaccination behavior. Some states make it difficult to access data or provide low-resolution data of limited value for identifying vaccination behavior.