Vaccine-Preventable Diseases

Vaccine-preventable diseases are infectious diseases whose incidence can be reduced or eliminated by vaccination, which primes the adaptive immune system to recognise a pathogen before natural exposure. They illustrate how deliberately engaging host immunity can change the burden of infection for both individuals and whole populations.

Definition

Vaccine-preventable diseases are communicable diseases for which immunisation can induce protective adaptive immunity, lowering the risk of infection or severe disease in vaccinated individuals and reducing transmission within populations.

Scope

This topic covers the immunologic basis of vaccination, the concept of correlates of protection, how vaccine effectiveness is measured, and the population-level effects of immunisation including herd immunity, together with the social phenomenon of vaccine confidence. It is a reference overview rather than a schedule or clinical recommendation.

Core questions

• How does vaccination generate protective immunity against a pathogen?
• What is a correlate of protection and why is it useful?
• How is vaccine effectiveness measured in real populations?
• How does vaccination protect communities beyond the individual?

Key concepts

• Immunologic memory
• Correlates of protection
• Vaccine efficacy versus effectiveness
• Herd immunity
• Test-negative design
• Vaccine confidence and hesitancy

Mechanisms

Vaccination exposes the immune system to antigens derived from a pathogen, eliciting an adaptive response and immunologic memory so that a subsequent natural encounter is met by a faster, stronger defense. The immune markers that reliably predict this protection are termed correlates of protection, and they may be simple antibody thresholds or more complex combinations of humoral and cellular responses (Plotkin, 2013). At the population level, when a sufficient fraction of a community is immune, transmission chains are interrupted and even unvaccinated individuals gain indirect protection, the basis of herd immunity.

Clinical relevance

Vaccine-preventable diseases show how priming host immunity changes the epidemiology of infection, and understanding correlates of protection and effectiveness is part of appraising immunisation evidence. This entry is educational; it describes principles and population effects and does not constitute a vaccination schedule or individualised medical advice.

Epidemiology

Immunisation has produced some of the largest reductions in infectious-disease burden in modern public health, including the eradication of smallpox and steep declines in diseases such as measles and polio where coverage is high. Vaccine effectiveness in real-world settings is commonly estimated with designs such as the test-negative design (Jackson & Nelson, 2013), while gaps in vaccine confidence can lower coverage and allow resurgence of previously controlled diseases (Larson et al., 2011).

History

Vaccination has roots in the eighteenth-century practice of inducing protective immunity against smallpox, and the twentieth century brought vaccines against many major pathogens and the global eradication of smallpox. More recent work has formalised the immunologic correlates that underlie protection and the epidemiologic methods used to measure vaccine effectiveness, while the social determinants of uptake have become a recognised challenge to sustaining control (Plotkin, 2013; Larson et al., 2011).

Debates

How should vaccine confidence and hesitancy be addressed?

Sustaining high coverage depends not only on vaccine performance but on public trust, and the determinants of confidence and the most effective ways to strengthen it remain an active area of study and policy.

Key figures

• Stanley Plotkin
• Heidi Larson
• Michael Jackson

Seminal works

• plotkin-2013
• larson-2011

Frequently asked questions

What makes a disease vaccine-preventable?

A disease is vaccine-preventable when a vaccine can prime the immune system to recognise the responsible pathogen and mount a protective response, lowering the chance of infection or severe illness. Many major infectious diseases fall into this category.

What is herd immunity?

Herd immunity is the indirect protection that arises when a large enough share of a population is immune, which interrupts transmission so that even unvaccinated people are less likely to be exposed. It is one of the main reasons vaccination has population-wide benefits.