Module 3

• Vaccines may not provide immediate or lasting protection, necessitating additional doses or explaining why illness can still occur post-vaccination.
• Vaccines do not guarantee 100% protection; some individuals may still get infected due to non-response or waning immunity.

Vaccine Failure Types

• Primary vaccine failure: Occurs when an individual doesn't develop an adequate immune response after the initial vaccination.
• Measles, mumps, and rubella (MMR) vaccine example: Approximately 10% of individuals do not respond to the measles component after the first dose.
• A second MMR dose is administered to provide a second opportunity for those who did not initially respond to build immunity.
• For those who initially responded to the first MMR dose, the viruses in the second vaccine are neutralized by existing antibodies.
• Secondary vaccine failure: Occurs when an individual's immunity weakens over time after an initial adequate immune response.
• This is a common characteristic of inactivated vaccines, necessitating multiple doses or booster shots.

Vaccine Reactions

• Local reactions: More common with inactivated vaccines containing adjuvants (e.g., pain, redness, swelling at the injection site).
• Systemic reactions: More common after live vaccines, generally less severe, and less likely with subsequent doses (e.g., fever, headache, loss of appetite).
• Allergic reactions: Rare but can occur, such as anaphylaxis or severe systemic allergic reactions.
• These reactions involve the body's immune response and may include symptoms like difficulty breathing, facial/throat swelling, rapid heartbeat, and dizziness.

Adverse Reactions and Side Effects

• All side effects are considered adverse events, but not all adverse events are typical or expected side effects.
• WHO definition of Adverse Effect Following Immunization (AEFI): Any untoward medical occurrence after immunization, not necessarily causally related to the vaccine.
• "Adverse events" and "side effects" are often used interchangeably, but they have subtle differences.

Side Effects

• Known, often expected outcomes alongside the primary effect of a treatment or medication.
• Can range from mild to severe and temporary to permanent.
• Examples: nausea from chemotherapy or drowsiness from antihistamines.

Adverse Events

• Undesirable experiences associated with the use of a medical product in a patient.
• Can be unexpected and not necessarily related to the medication's known side effects.
• Broad range, including mild side effects to serious outcomes like organ damage or life-threatening reactions.

Yellow Card and Black Triangle Schemes

• The Yellow Card scheme records adverse incidents related to medicines and medical devices.
• The Black Triangle Scheme identifies closely monitored medicines requiring reporting of suspected adverse reactions.

Yellow Card Scheme

• Encourage reporting adverse reactions to vaccines when a causal link is suspected, even if uncertain, as encouraged by the MHRA.
• Report all suspected adverse reactions, especially in children, for thorough assessment and monitoring.

Black Triangle Scheme

• Newly licensed vaccines are marked with a 'black triangle' symbol, triggering enhanced surveillance.
• Report all adverse reactions, serious and non-serious, for these products, while only serious reactions need reporting for vaccines on the market for over two years.

Anaphylaxis Definition

• The World Allergy Organisation Anaphylaxis Committee defines anaphylaxis as: “A serious systemic hypersensitivity reaction that is usually rapid in onset and may cause death Severe anaphylaxis is characterised by potentially life-threatening compromise in airway, breathing and/or the circulation, and may occur without typical skin features or circulatory shock being present”

Anaphylaxis Process

• Anaphylaxis is a serious and potentially life-threatening allergic reaction
• Initial exposure to an allergen (e.g., foods, insect stings, medications) can cause the immune system to mistakenly identify it as a threat.
• This triggers the production of immunoglobulin E (IgE) antibodies.
• Upon subsequent exposure to the same allergen, IgE antibodies recognize it and bind to it.
• This activates mast cells and basophils by attaching to their surface receptors.
• Activated cells release chemical mediators like histamine, leukotrienes, and cytokines.
• These chemicals cause the symptoms of anaphylaxis, affecting multiple organ systems, and can lead to hives, itching, swelling, difficulty breathing, dizziness, nausea, and more.