Vaccinations

Overview – Vaccinations

Vaccinations are one of the most impactful and cost-effective public health interventions, responsible for the prevention of millions of deaths globally each year. They work by stimulating the immune system to generate protective responses without the individual having to experience the disease itself. Vaccinations also contribute to herd immunity, which protects vulnerable and unvaccinated individuals within the community.

How Vaccines Work

Individual Protection

• Vaccines introduce antigenic material to stimulate the production of antibodies and memory cells, without causing disease.
• On re-exposure to the pathogen, the immune system mounts a faster, stronger secondary immune response, preventing illness.

Herd Immunity

• When a critical proportion of the population is vaccinated, transmission chains are broken.
• Provides indirect protection to those who cannot be vaccinated (e.g. immunocompromised individuals).

Principles of Vaccine Development and Use

1. Separate disease-causing effects from immune-generating effects.
2. Administer to susceptible individuals to provoke an immune response.
3. Result is individual immunity.
4. Outcome over time is herd immunity across the population.

Contraindications to Vaccination

Absolute

• Documented anaphylactic reaction to a vaccine or its components.

Relative (Risk vs Benefit)

• Immunocompromised (especially for live vaccines).
• Pregnancy (avoid live vaccines).
• Fever >38.5°C.
• Recent live vaccine within past 4 weeks.
• Recent blood product administration.
• History of Guillain-Barré Syndrome (esp. with influenza vaccine).

Note: These are not reasons to avoid all vaccines. Patients retain the freedom of choice in vaccination decisions.

Types of Vaccines

Live Attenuated Vaccines

• Live organisms weakened to remove pathogenicity.
• Pros: Strong, long-lasting immunity (1–2 doses).
• Cons: May cause disease in pregnant or immunocompromised patients.

Inactivated (Killed) Vaccines

• Contain non-replicating, dead organisms.
• Pros: Cannot cause disease, fewer side effects.
• Cons: Weaker response, requires boosters.

Acellular / Toxoid / Subunit Vaccines

• Use purified antigens or inactivated toxins.
• Pros: Safer, lower risk of adverse effects.
• Cons: Less immunogenic, may need adjuvants or conjugates.

Recombinant Protein Vaccines

• Engineered via yeast/bacteria to express pathogen proteins.
• Pros: Safe, targeted.
• Cons: Needs adjuvants, less immunogenic alone.

Nucleic Acid Vaccines (e.g. mRNA)

• Deliver synthetic genetic code to host cells → produce antigenic proteins.
• Pros: Targeted, no live organism, no risk of infection.
• Cons: High cost, temperature sensitive, new tech.

Antibody Response: Primary vs Secondary

• Primary Response: After first exposure, slow antibody development.
• Secondary Response: Faster and stronger response upon re-exposure due to memory B cells.
• Vaccines mimic primary exposure to build immune memory safely.

Key Vaccine-Preventable Diseases

Measles

• Virus: Morbillivirus
• Transmission: Airborne droplets
• Incubation: 10–14 days
• Symptoms: Fever, cough, conjunctivitis, Koplik spots, widespread rash
• Complications: Otitis media, pneumonia, encephalitis
• Vaccine: Live attenuated, part of MMRV (measles, mumps, rubella, varicella)
• Schedule: 12 months & 18 months
• Note: Not given in pregnancy. Maternal antibodies protect infants <9 months.

Rubella

• Virus: Rubivirus
• Transmission: Droplet + mucous membranes
• Incubation: 14–21 days
• Symptoms: Often mild or asymptomatic, rash, lymphadenopathy, arthralgia
• Complications: Congenital Rubella Syndrome (CRS) – 90% risk if infection in first trimester
• Vaccine: Live attenuated; part of MMRV
• Note: Essential for women of childbearing age

Notable Vaccines and Diseases Prevented

The Cold Chain

What is the Cold Chain?

• The continuous refrigeration of vaccines during storage and transport to maintain potency.

Cold Chain Stages

• Manufacture → Supply → Distribution → Clinic → Fridge → Patient

Freeze-Sensitive Vaccines

• Tetanus, DTP, Hib, Hep A/B, Influenza, Pneumococcal

Heat/Light-Sensitive Vaccines

• BCG, Oral Polio, MMR

Fridge Thermometers

• Must record min/max temperature over 24 hours
• Mercury or digital thermometers preferred
• Probe should be placed centrally in fridge, ideally within foam box

Transport Protocol

• Use iceboxes, sweating ice packs, shredded newspaper
• Avoid sunlight, minimise travel time, secure during transit
• Record temperatures at every step
• Deliver only when staff present

Storage Protocol

• Use locked fridges, not shared with food
• Place vaccines centrally (not door/bottom shelves)
• Rotate stock (use oldest first)
• Max 50% space usage for air circulation
• Daily temp checks
• Suspect breach? Label “Do Not Use” and contact supplier

Summary – Vaccinations

Vaccinations remain the most effective public health tool to prevent infectious diseases and reduce morbidity and mortality worldwide. Vaccinations offer both individual protection and herd immunity, and are delivered in a range of forms including live attenuated, inactivated, subunit, recombinant and nucleic acid types. Vaccination schedules, contraindications, and proper cold chain storage are essential for safe and effective immunisation. For a broader context, see our Microbiology & Public Health Overview page.