Why are vaccines important for public health?

Vaccines are a foundational public health tool because they prevent disease, reduce deaths, and stabilize societies by interrupting transmission chains. The World Health Organization reports that immunization averts an estimated two to three million deaths every year, a figure that reflects reductions in illnesses that formerly caused widespread mortality and long-term disability. The eradication of smallpox under the global campaign led by Donald A. Henderson at the Centers for Disease Control and Prevention demonstrates how coordinated vaccination can eliminate a pathogen entirely, ending deaths and long-term economic burdens tied to that disease.

How vaccines protect individuals and communities
Vaccination works by priming the immune system to recognize and respond to specific pathogens before natural infection occurs. This direct protection reduces individuals’ risk of severe disease, hospitalization, and death. Widespread uptake creates indirect protection known as herd immunity: when a sufficient portion of a population is immune, chains of transmission are interrupted and vulnerable people who cannot be vaccinated—infants, immunocompromised individuals—are protected. Paul Offit at the Children’s Hospital of Philadelphia has documented how high coverage levels for childhood vaccines transform population health by preventing outbreaks that would otherwise overwhelm health systems.

Causes of success and limits to control
The success of vaccination programs depends on vaccine effectiveness, delivery infrastructure, and public confidence. Technological advances in vaccine design and manufacturing have improved safety and durability of protection, while health system investments—cold chains, trained staff, surveillance—enable distribution to urban and remote areas alike. Conversely, vaccine hesitancy driven by misinformation, distrust, or past malpractice can erode coverage. Heidi J. Larson at the London School of Hygiene and Tropical Medicine researches how social and cultural dynamics influence confidence, showing that rumors and perceived disrespect from health authorities contribute to refusal or delay.

Consequences of low coverage and broader impacts
When coverage falls, preventable diseases resurge, causing avoidable illness and death and imposing economic costs from lost productivity and increased healthcare spending. Poliomyelitis cases have fallen by more than 99 percent since the launch of the Global Polio Eradication Initiative, according to the World Health Organization, illustrating the large health gains feasible with persistent immunization. In contrast, regional declines in measles vaccination have been followed by outbreaks that disproportionately affect marginalized communities lacking access to care.

Cultural, environmental, and territorial nuances matter in program design. In conflict zones and remote territories, maintaining cold chains and safe access is logistically and ethically challenging; tailored strategies used by humanitarian agencies and public health teams help reach displaced and rural populations. Vaccination programs also have environmental and antimicrobial implications: by preventing bacterial and viral infections, vaccines reduce antibiotic use and thereby slow the development of antimicrobial resistance, a global environmental-health concern highlighted by public health researchers at Johns Hopkins Bloomberg School of Public Health.

Evidence from clinical trials, historical eradication campaigns, and population surveillance consistently shows that vaccines are among the most cost-effective and equitable interventions in public health when delivered with attention to social context and system capacity. Maintaining investment, addressing cultural concerns, and strengthening delivery infrastructure are essential to sustain these benefits.