Immunization Overview

Immunization

• Immunization is a method of acquiring protection against diseases.
• This can be done actively or passively.

Active Immunity

• Active immunity involves exposure to an infectious agent, leading to the production of antibodies (Abs) or sensitized T cells.
• Immunity develops gradually but lasts a long time due to memory.
• Natural active immunity results from infections (clinical or subclinical.)
• Artificial active immunity occurs after vaccination.

Passive Immunity

• Passive immunity involves transferring pre-made antibodies.
• It provides quick protection, but immunity is short-lived.
• Natural passive immunity occurs when antibodies pass from mother to fetus via the placenta (IgG) or in colostrum (IgA).
• Artificial passive immunity is used in disease prophylaxis or treatment. This includes antitoxin serum (e.g., diphtheria, tetanus), and immunoglobulin injections (e.g., measles).
• Note: Passive active immunity involves administering both immunoglobulin and vaccine simultaneously at different body sites (e.g., needle prick with HBV+ve blood).

Types of Vaccines

• Killed or Inactivated Vaccines: These vaccines use killed or inactivated forms of pathogens.
  • Examples include: Sinovac COVID-19 Vaccine, TAB vaccine (typhoid and paratyphoid), Salk vaccine (polio), and rabies vaccines.
• Living Attenuated Vaccines: Weakened versions of the pathogen are used.
  • Examples include: BCG vaccine (TB), Sabin vaccine (polio), MMR vaccine (measles, mumps, rubella), 17D vaccine (yellow fever), and rabies vaccine (animals).
• Toxoids: These vaccines use toxins from bacteria, which are deactivated to retain immunogenicity.
  • Examples include: vaccines for diphtheria and tetanus.
• Bacterial or Viral Components: Components of the pathogen (e.g., capsule, surface proteins) are used.
  • Examples include: Meningococcal, pneumococcal, H. influenzae type b vaccines (with carrier protein, diphtheria toxoid), influenza virus vaccine (using HA and neuraminidase), and B. pertussis vaccine (purified protein).
• Recombinant Antigen Vaccines: These vaccines use cloned genes for the antigen, often recombined into a vector (e.g., E. coli or yeast).
  • Examples include: Hepatitis B virus (HBV), Herpes simplex virus (HSV), and foot-and-mouth disease vaccines.
• Recombinant Avirulent Vectors: The gene for the antigen is inserted into the genome of a weakened (avirulent) vector, such as a vaccinia virus.
  • Examples include: HBV vaccines, Oxford/AstraZeneca COVID-19 vaccine, Johnson & Johnson's Janssen COVID-19 Vaccine, Sputnik V vaccine–all are adenovirus vector vaccines.
• Synthetic Peptide Vaccines: Peptides that mimic the protective antigen of a microbe are used.
  • Example: Influenza virus.
• Attenuated Non-reverting Mutant Vaccines: Genetic engineering is used to irreversibly weaken viruses.
• DNA Vaccines: DNA encoding an antigen is injected directly, using a plasmid vector.

Advantages & Disadvantages (Killed & Live-attenuated Vaccines)

• Killed Vaccines:*
• Advantages: Short-lasting immunity; easy to produce; heat-stable, therefore doesn't need cold storage; safe for pregnant and immunocompromised persons.
• Disadvantages: Needs booster shots; doesn't stimulate cell-mediated (immunity) or local immunity.
• Live Attenuated Vaccines:*
• Advantages: Long-lasting immunity, does not require boosters; can be excreted to immunize others (herd immunity); and often induces cell-mediated and local immunity).
• Disadvantages: Heat-labile, requires cold storage; potential risk of reverting to virulence; may cause diseases in immunocompromised individuals; expensive and difficult to prepare.

COVID-19 Vaccines

• COVID-19 is caused by SARS-CoV-2.
• SARS-CoV-2 is a coronavirus.
• Coronavirus structure: Envelope with spike glycoprotein, RNA and protein.
• Various types of COVID-19 vaccines exist—RNA, viral vectors, inactivated viruses, etc—with varying storage needs and efficacies.
• Different COVID-19 variants (e.g., Alpha, Beta, Delta, Omicron) affect vaccine effectiveness.

Vaccine Storage

• Storage temperatures vary based on vaccine type.

Clinical Characterization of COVID-19

• COVID-19 symptoms can range from asymptomatic to multi-organ manifestations.
• Mild cases involve things like fever, cough and fatigue; severe cases involve things like acute respiratory distress syndrome, needing mechanical ventilation.

Immune Response (Natural Infection-induced Immunity)

• Natural infection triggers immune responses to COVID-19.
• Cells detect antigens (virus) and trigger immune responses.
• T-cells and antibodies are key players in the process.

Variants

• Variants of interest that may change receptor binding, or decrease immune response after infection or vaccination.
• Variants of concern exhibit increased transmissibility, more severe disease, reduced immunity or vaccine/treatment effectiveness. These include Delta and Omicron.

This quiz explores the concepts of immunization, focusing on active and passive immunity. Discover how active immunity develops through exposure to infectious agents and how passive immunity provides quick but short-lived protection. Test your knowledge on different forms of immunity and their implications.