Direct and indirect effects
Immunizations against specific infectious diseases protect individuals against infection and thereby prevent symptomatic illnesses. Specific vaccines may blunt the severity of clinical illness (e.g., rotavirus vaccines and severe gastroenteritis) or reduce complications (e.g., zoster vaccines and postherpetic neuralgia). Some immunizations also reduce transmission of infectious disease agents from immunized people to others, thereby reducing the impact of infection spread. This indirect impact is known as herd immunity. The level of immunization in a population that is required to achieve indirect protection of unimmunized people varies substantially with the specific vaccine.
Since childhood vaccines have become widely available in the United States, major declines in rates of vaccine-preventable diseases among both children and adults have become evident (Table 5-2). For example, vaccination of children <5 years of age against seven types of Streptococcus pneumoniae led to a >90% overall reduction in invasive disease caused by those types. A series of childhood vaccines targeting 13 vaccine-preventable diseases in a single birth cohort leads to prevention of 42,000 premature deaths and 20 million illnesses and saves nearly $70 billion (U.S.).
Control, elimination, and eradication of vaccine-preventable diseases
Immunization programs are associated with the goals of controlling, eliminating, or eradicating a disease. Control of a vaccine-preventable disease reduces poor illness outcomes and often limits the disruptive impacts associated with outbreaks of disease in communities, schools, and institutions. Control programs can also reduce absences from work for ill persons and for parents caring for sick children, decrease absences from school, and limit health care utilization associated with treatment visits.
Elimination of a disease is a more demanding goal than control, usually requiring the reduction to zero of cases in a defined geographic area but sometimes defined as reduction in the indigenous sustained transmission of an infection in a geographic area. As of 2013, the United States had eliminated indigenous transmission of measles, rubella, poliomyelitis, and diphtheria. Importation of pathogens from other parts of the world continues to be important, and public health efforts are intended to react promptly to such cases and to limit forward spread of the infectious agent.
Eradication of a disease is achieved when its elimination can be sustained without ongoing interventions. The only vaccine-preventable disease of humans that has been globally eradicated thus far is smallpox. Although smallpox vaccine is no longer given routinely, the disease has not reemerged naturally because all chains of human transmission were interrupted through earlier vaccination efforts and humans were the only natural reservoir of the virus. Currently, a major health initiative is targeting the global eradication of polio. Sustained transmission of polio has been eliminated from most nations but has never been interrupted in three countries—Afghanistan, Nigeria, and Pakistan—while recent outbreaks in Syria and the Horn of Africa underscore that other countries remain at risk for importation until these reservoirs have been addressed. Detection of a case of disease that has been targeted for eradication or elimination is considered a sentinel event that could permit the infectious agent to become reestablished in the community or region. Therefore, such episodes must be promptly reported to public health authorities.
Outbreak detection and control
Clusters of cases of a vaccine-preventable disease detected in an institution, a medical practice, or a community may signal important changes in the pathogen, vaccine, or environment. Several factors can give rise to increases in vaccine-preventable disease, including (1) low rates of immunization that result in an accumulation of susceptible people (e.g., measles resurgence among vaccination abstainers); (2) changes in the infectious agent that permit it to escape vaccine-induced protection (e.g., non-vaccine-type pneumococci); (3) waning of vaccine-induced immunity (e.g., pertussis among adolescents and adults vaccinated in early childhood); and (4) point-source introductions of large inocula (e.g., food-borne exposure to hepatitis A virus). Reporting episodes of outbreak-prone diseases to public health authorities can facilitate recognition of clusters that require further interventions.
Recognition of suspected cases of diseases targeted for elimination or eradication—along with other diseases that require urgent public health interventions, such as contact tracing, administration of chemo- or immunoprophylaxis, or epidemiologic investigation for common-source exposure—is typically associated with special reporting requirements. Many diseases against which vaccines are routinely used, including measles, pertussis, Haemophilus influenzae type b invasive disease, and varicella, are nationally notifiable. Clinicians and laboratory staff have a responsibility to report some vaccine-preventable disease occurrences to local or state public health authorities according to specific case-definition criteria. All providers should be aware of state or city disease-reporting requirements and the best ways to contact public health authorities. A prompt response to vaccine-preventable disease outbreaks can greatly enhance the effectiveness of control measures.
Several international health initiatives currently focus on reducing vaccine-preventable diseases in regions throughout the world. These efforts include improving access to new and underutilized vaccines, such as pneumococcal conjugate, rotavirus, human papillomavirus (HPV), and meningococcal A conjugate vaccines. The American Red Cross, the World Health Organization (WHO), the United Nations Foundation, the United Nations Children’s Fund (UNICEF), and the Centers for Disease Control and Prevention (CDC) are partners in the Measles & Rubella Initiative, which targets reduction of worldwide measles deaths by 95% from 2000 to 2015. During 2000–2011, global measles mortality rates declined by 71%—i.e., from an estimated 548,000 deaths in 2000 to 158,000 deaths in 2011. Rotary International, UNICEF, the CDC, and the WHO are leading partners in the global eradication of polio, an endeavor that reduced the annual number of paralytic polio cases from 350,000 in 1988 to <250 in 2012. The GAVI Alliance and the Bill and Melinda Gates Foundation have brought substantial momentum to global efforts to reduce vaccine-preventable diseases, expanding on earlier efforts by the WHO, UNICEF, and governments in developed and developing countries.
Enhancing immunization in adults
Although immunization has become a centerpiece of routine pediatric medical visits, it has not been as well integrated into routine health care visits for adults. This chapter focuses on immunization principles and vaccine use in adults. Accumulating evidence suggests that immunization coverage can be increased through efforts directed at consumer-, provider-, institution-, and system-level factors. The literature suggests that the application of multiple strategies is more effective at raising coverage rates than is the use of any single strategy.
Recommendations for adult immunizations
The CDC’s Advisory Committee on Immunization Practices (ACIP) is the main source of recommendations for administration of vaccines approved by the U.S. Food and Drug Administration (FDA) for use in children and adults in the U.S. civilian population. The ACIP is a federal advisory committee that consists of 15 voting members (experts in fields associated with immunization) appointed by the Secretary of the U.S. Department of Health and Human Services; 8 ex officio members representing federal agencies; and 26 nonvoting representatives of various liaison organizations, including major medical societies and managed-care organizations. The ACIP recommendations are available at www.cdc.gov/vaccines/hcp/acip-recs/. These recommendations are harmonized to the greatest extent possible with vaccine recommendations made by other organizations, including the American College of Obstetricians and Gynecologists, the American Academy of Family Physicians, and the American College of Physicians.
Adult immunization schedules
Immunization schedules for adults in the United States are updated annually and can be found online (www.cdc.gov/vaccines/schedules/hcp/adult.html). In January, the schedules are published in American Family Physician, Annals of Internal Medicine, and Morbidity and Mortality Weekly Report (www.cdc.gov/mmwr). The adult immunization schedules for 2013 are summarized in Fig. 5-1. Additional information and specifications are contained in the footnotes to these schedules. In the time between annual publications, additions and changes to schedules are published as Notices to Readers in Morbidity and Mortality Weekly Report.
Recommended adult immunization schedules, United States, 2013. For complete statements by the Advisory Committee on Immunization Practices (ACIP), visit www.cdc.gov/vaccines/hcp/acip-recs/.