explain how vaccination programmes can help to control the spread of infectious diseases

Antibodies and \cdot accination

Learning Objective

Explain how vaccination programmes can help to control the spread of infectious diseases.

1. The Role of Antibodies in Immunity

When a pathogen enters the body, the adaptive immune system produces specific antibodies that bind to antigens on the pathogen’s surface. This binding can:

• Neutralise toxins or viruses, preventing them from entering cells.
• Opsonise bacteria, enhancing phagocytosis by macrophages.
• Activate the complement cascade, leading to lysis of the pathogen.

Memory B cells generated during the primary response enable a rapid and amplified secondary response upon re‑exposure.

2. How \cdot accination Works

Vaccines introduce an antigenic stimulus that mimics a natural infection without causing disease. This stimulates the production of antibodies and memory cells, providing immunity that can be recalled quickly if the real pathogen is encountered.

3. Types of \cdot accines

4. How \cdot accination Programs Control Disease Spread

1. Induction of Herd Immunity

   When a high proportion of the population is immune, the effective reproduction number (\$R_e\$) falls below 1, preventing sustained transmission.

   \$Re = R0 \times (1 - p)\$

   where \$R_0\$ is the basic reproduction number and \$p\$ is the proportion immune.

2. Reduction of Disease Incidence and Severity

   Vaccinated individuals are less likely to contract the disease, and if infection occurs, symptoms are usually milder.

3. Interrupting Transmission Chains

   Vaccination reduces the number of susceptible hosts, breaking chains of infection, especially in densely populated settings such as schools.

4. Protection of \cdot ulnerable Groups

   People who cannot be vaccinated (e.g., infants, immunocompromised) are protected indirectly through herd immunity.

5. Economic and Social Benefits

   Fewer cases mean reduced healthcare costs, less absenteeism from work or school, and lower mortality.

5. Factors Influencing the Success of \cdot accination Programs

• Vaccine coverage rates – target thresholds vary by disease (e.g., >95 % for measles).
• Vaccine efficacy – proportion of vaccinated individuals who develop protective immunity.
• Population demographics – age structure, migration, and birth rates affect herd immunity thresholds.
• Public confidence and misinformation – affect uptake.
• Logistical considerations – cold‑chain maintenance, access to remote areas.

6. Case Study: Measles Elimination Efforts

Measles has a high \$R_0\$ (12–18), requiring >95 % vaccination coverage for herd immunity. Countries that achieved >95 % coverage saw a >99 % reduction in cases within a decade.

Key strategies included:

• Routine two‑dose MMR schedule at 12 months and 4–5 years.
• Supplementary immunisation activities during outbreaks.
• Surveillance and rapid response teams.

7. Summary

Vaccination programmes harness the body’s ability to produce antibodies and memory cells, creating individual immunity and, when coverage is high, herd immunity. By reducing the number of susceptible hosts, these programmes lower \$R_e\$, interrupt transmission chains, protect vulnerable individuals, and provide broad societal benefits.