Vaccines and Vaccination

Vaccines and Vaccination - Vaccines aim to:

• Prevent disease symptoms.
• Prevent disease transmission.
• Eradicate the disease completely.

Successful Eradication: Smallpox

• Cowpox (vaccinia) vaccine was the first successful vaccine.
• Developed by Doctor Jenna based on the observation that milkmaids infected with cowpox were resistant to smallpox.
• Eradication declared worldwide in 1980 through vaccination and quarantine.
• Smallpox is a fatal disease with pustular lesions over the body.

Factors Contributing to Successful Eradication

• Disease limited to humans.
• No long-term carriers.
• Disease always recognisable (distinctive symptoms).
• Fewer serotypes and variants.
• Stable, cheap, and effective vaccine.

Vaccine Stability and Cost

• Vaccines need to be stable for easy transport, which can be challenging, especially in remote areas without refrigeration.
• The "cold chain" involves transporting vaccines with refrigeration to remote communities.
• This increases complexity and cost.
• Vaccines need to be affordable for all countries.
• Global surveillance is crucial due to international mobility facilitated by organizations like the World Health Organization (WHO).

Current Eradication Efforts

• Diseases targeted for eradication:
• Polio
• Measles
• Rubella
• Typhoid
• Measles outbreaks are rising due to lack of vaccination.
• Polio is close to eradication.

Polio Vaccines

• Two types are available:
• Inactivated or killed Salk vaccine (injected) $IgG$: Triggers an immune response and production of immunoglobulins like $IgG$ and immune memory, but requires trained professionals for administration.
• Attenuated or oral polio vaccine (OPV): Replicates in the gut, shedding vaccine-derived virus to immunize others in the community.

Oral Polio Vaccine (OPV) Details

• OPV contains weakened strains of the virus that replicate in the intestine, building up antibodies (mucosal or intestinal immunity).
• The weakened viruses excreted spread protection in the community by passively immunizing others.
• OPV breaks the chain of infection and is easily administered by putting two drops into the mouth.

Inactivated Polio Vaccine (IPV) Details

• Administered through injection and contains killed strains of the virus.
• Produces antibodies in the blood but does little to stop the virus from spreading from the intestine to others.
• Becomes more important as we move closer to a polio-free world.

Vaccination Coverage

• Over 95% of people need to be vaccinated to halt polio circulation.
• Global Polio Eradication Initiative strengthens routine immunization programs.

Challenges and Risks of OPV

• The shared virus from OPV can spread via contaminated water/food sources.
• In areas with low vaccination, the virus can undergo genetic mutations and revert to a paralytic form.
• High vaccination levels and eventual withdrawal of OPV are necessary.

Polio Eradication in Africa

• In August 2020, the WHO declared Africa free of wild polio after no cases since 2016.
• Achieved through concerted efforts, reaching 95% vaccination coverage.
• War and disturbances in the Middle East have caused a recent rise in polio cases.

Monitoring Polio

• In Australia, monitoring includes:
• Notification of symptomatic cases.
• Wastewater testing in sewage plants for pathogens, including polio.
• During COVID-19, wastewater testing also monitored COVID levels.

Herd Immunity

• Community-based immunity achieved when sufficient population coverage prevents outbreaks.
• For polio, 95% vaccination is the target.
• Protects those who cannot be vaccinated, such as pregnant women, young children, and immunocompromised individuals.
• Diagram illustrating reduced disease spread with high vaccination rates.

Infectious Diseases and Poverty

• Main infectious diseases causing deaths:
• Tuberculosis
• Malaria
• Diarrheal diseases (leading cause of death in children under 5 in developing countries)
• Pneumonia
• Measles
• HIV/AIDS
• These are often illnesses of poverty, related to cost-effectiveness of vaccination and treatment, education, sanitation, water and food sources, and waste disposal.
• Example: HIV/AIDS in Africa where families may share medication due to cost, resulting in suboptimal doses and development of AIDS.

Types of Immunization

• Passive Immunization:
• Injection containing immunoglobulin $Ig$.
• Preventative measure with preformed antibodies.
• Provides quick protection but no long-term memory.
• Used in antitoxins (tetanus, gas gangrene), hepatitis A, measles, and shingles vaccines.
• Active Immunization:
• Antigen introduced to the body.
• Triggers cell-mediated and humoral immune responses.
• Creates memory cells for quicker and greater response upon re-exposure.

Vaccine Mechanisms

• Most vaccines contain a component of the microorganism that causes harm.
• Live, killed, subunit, and mRNA vaccines are used.

COVID-19 Vaccines as Examples

• AstraZeneca: Live, attenuated vaccine using an adenovirus modified to produce the spike protein of COVID-19.
• Pfizer: mRNA vaccine containing the code for making the spike protein.
• All vaccines introduce the immune system to the spike protein through different mechanisms.

Immunoglobulin Response $IgM$

• Produced quickly upon exposure to the antigen.
• Levels drop off rapidly. $IgG$
• Main defensive immunoglobulin.
• Produced a few days after exposure.
• Levels drop over time but remain stable.
• Booster shots increase $IgG$ levels with each subsequent dose, leading to lifelong immunity in some cases.
• Different organisms trigger responses to varying extents.

COVID-19 Vaccination and Immunoglobulin

• COVID-19 vaccines target the spike protein, inducing $IgG$, $IgM$, and $IgA$.
• IgA is distributed on mucosal surfaces (respiratory defense). * Booster shots mainly boost $IgG$, not $IgA$.
• Vaccines reduce severe disease but are less effective at preventing transmission.

COVID-19 and Eradication Considerations

• Not limited to humans (found in other animals).
• Has asymptomatic carriers.
• Has many variants.
• Vaccine cost is high for some countries.
• Effective at attenuating severe disease.
• Considered a safe vaccine.
• Global monitoring was inconsistent.
• Disease is not easily detected (symptoms resemble flu, cold, or hay fever).
• Vaccine requires cold storage.

Mandatory Vaccinations for Healthcare Workers

• Healthcare workers are more likely to contact infectious organisms.
• VU (College of Sport and Exercise Science) requires clinical placements to have:
• Evidence of immunity to certain diseases.
• Vaccination against certain diseases.
• Highly recommended: COVID-19 booster shots *Compulsory vaccinations:
• Hepatitis B: Blood-borne; course of three vaccinations for adults; doctor's confirmation of antibody levels required.
• Influenza: Respiratory infection; required for the current clinical year; offered at most chemists and free at Headspace (page 25).
• If a person has a hepatitis B infection previously or has a chronic hepatitis B, protect them from viral infections.