What is Vaccine, Vaccine designing and types of vaccine in Immunology

 INTRODUCTION

• VACCINE - A vaccine is a biological preparation designed to provide immunity against a specific infectious disease.
• Contains certain agents that not only resembles a disease- causing microorganism but it also stimulates body’s immune system recognize the foreign agents.
• It typically contains:
• Antigens: Components derived from pathogens (bacteria or viruses) that stimulate/trigger the immune system.
• Adjuvants: Substances that enhance the body's immune response to the antigen.
• Preservatives: To maintain vaccine stability and prevent contamination (in multi-dose vials)
• Stabilizers: To help the vaccine remain unchanged during storage

IMPORTANCE: -

• The body develops immunity
  
• Infectious disease is prevented.
  
• Certain diseases are treated

Small pox, polio are eradicated from humans by vaccines

WHOLE ORGANISMS VACCINE

• A whole organism vaccine is a type of vaccine that uses an entire microorganism (bacterium or virus) to stimulate an immune response. This microorganism can be either inactivated (killed) or attenuated (weakened), meaning it is not capable of causing disease in its current form but still elicits a protective immune response.

Types of Whole Organism Vaccines:

• Inactivated (Killed) Vaccines: Use microorganisms that have been killed or inactivated so they cannot cause disease.
• Attenuated (Live) Vaccines: Use live but weakened microorganisms that are not capable of causing disease in healthy individuals.

•  Stimulate a Strong Immune Response: Whole organism vaccines can induce a robust immune response because they present the entire pathogen to the immune system, including multiple antigens.
•  Provide Long-Lasting Immunity: These vaccines can often provide long-term immunity due to the comprehensive immune stimulation. Live attenuated vaccines, in particular, tend to offer prolonged protection.
•  Potential for Cross-Protection: The broad antigen exposure in whole organism vaccines may provide protection against multiple strains or related pathogens.
•  Production and Storage Considerations: The production and storage of whole organism vaccines can be complex. Attenuated vaccines need careful handling to maintain their viability, while inactivated vaccines require precise inactivation methods.

KILLED VACCINES/ INACTIVATED VACCINES

•  Inactivated vaccines are made from microorganisms (virus/bacteria) that are killed by heat or formaldehyde.
• Safety: These vaccines can’t cause disease because the microbes are dead and can’t replicate.
• Structure: It’s important to keep the shape of the pathogen’s surface proteins intact to trigger an immune response.
•  Chemical inactivation with formaldehyde or various alkylating agents has been successful.
•  When the dead pathogen is injected into organism (host), it stimulates the production of antibodies without causing infection.
•  Immune response: - They can sometimes produce weaker and shorter-lasting immune responses, so multiple doses may be needed for effective protection.

Advantages: -

• Safer and more stable compared live attenuated vaccines.
• Since they have no live components there is no risk of infection.

Disadvantages: -

• There is a need for adjuvants
• Since responses are not long-lived multiple doses are required
• Less strong immune response compared to live vaccines. 

Examples: -

• Anthrax vaccine
• Cholera Vaccine
• Pertussis vaccine
• Influenza vaccine

LIVE ATTENUATED/ATTENUATED VACCINES

• The vaccines created by reducing the virulence and harmful effects of pathogens are called attenuated vaccines.
• These vaccines use live but weakened (less harmful) pathogens.
• How They Work: The weakening process makes the pathogen harmless while keeping its ability to trigger an immune response.
• Immune Response: They help the immune system create memory cells that protect against future infections by the same pathogen.

•       The weakening is usually done by growing the pathogen for a long time.

Methods followed to inactivate or attenuate the pathogen: -

1. Ultraviolent inactivation: - UV rays are used to inactivate the virus particles, since virus particles are small and UV- rays can reach the genetic material, inducing the dimerization of nucleic acids. Once the DNA dimerized the virus particles cannot replicate their genetic material.
2. Solvent detergent inactivation: - When the lipid coated viruses are treated with detergents, the detergents disrupt the interaction between the molecules in the lipid coat stopping the replication of virus because most of the virus cannot live without their lipid coating so they cannot survive when exposed to detergents. Some viruses may survive but cannot replicate thus becomes in effective. The detergent typically used is Triton-X 100.
3. Use of chemical agents: - Formaldehyde is used to inactivate the bacteria and virus.
4. Administration: Often administered via injection, but some are given orally (e.g., rotavirus vaccine).

ADVANTAGES: -

• Single dose administration.
• Generates both antibody-mediated and cell-mediated immunity.
• No need for adjuvants.
• Low cost and easy transportation.
• Rapid onset of action.
• Prolongs exposure to the immune system, enhancing response.
• Induces both cell-mediated and humoral immunity.

DISADVANTAGES: -

• Chances of Reversion of Virulence due to mutation which may lead to the development of infection.
• Can lead to side effects in certain individuals.
• Requires careful handling and storage, often necessitating refrigeration to maintain effectiveness

STEPS INVOLVED IN THE PRODUCTION OF WHOLE ORGANISM VACCINES: -

1. Pathogen selection: Choose a specific pathogen and ensure it's pure and free from contaminants.
2. Strain selection: Select a strain that causes pathogenicity and identify it using techniques like RFLP.
3. Culturing: Grow the strain in a controlled environment (petri dish) with suitable media.
4. Bulk production: Scale up production in fermenters with controlled conditions (pH, temperature, aeration).
5. Cell separation: Use techniques like centrifugation, chromatography, and filtration to separate cells from media.
6. Adjuvant addition: Add a substance (e.g., aluminium salts) to enhance the immune response.
7. Surfactant addition: Add a substance to keep ingredients blended and prevent settling/clumping.
8. Stabilizer addition: Add a substance (e.g., sugars, amino acids, gelatine) to prevent chemical reactions and sticking to the vial.
9. Lyophilization: Freeze-dry the vaccine to remove water content and preserve it.

LIMITATIONS OF CONVENTIONAL VACCINES/TRADITIONAL VACCINES:

• Cultivation Issues: Not all pathogens can be grown in culture, preventing the development of vaccines for certain diseases.
• Production Challenges: Vaccine production often involves low yields and high costs due to difficulties in culturing animal and human viruses.
• Safety Precautions: Strict safety measures are needed to prevent exposure to pathogenic agents during vaccine production.
• Risk of Reversion: Attenuated vaccines can revert to a virulent form, necessitating continuous testing to ensure safety.

❖   Limited Scope: Traditional vaccines cannot prevent all diseases, such as AIDS.

• Time-Consuming Development: The vaccine development process is lengthy and complex.
• Inactivation Risks: Some vaccines may be inadequately inactivated, potentially introducing live pathogens.
• Storage Issues: Many vaccines require refrigeration and have a limited shelf life, creating storage challenges, particularly in areas with unreliable electricity

SUBUNIT VACCINE

• Subunit Vaccines contain only specific parts or subunits of a pathogen (bacteria or virus) rather than the whole organism. These components are typically proteins or polysaccharides that can trigger an immune response without causing disease.
• Targeted Components: Includes only the essential parts of the pathogen necessary to elicit an immune response.

❑   Safety: Cannot cause the disease because the whole pathogen is not present.

❑   Administration: Usually given via injection.

      Types of Subunit Vaccines:

• Protein Subunit Vaccines: Contain purified proteins derived from the pathogen.

Examples:-

• Hepatitis B Vaccine: Contains the hepatitis B surface antigen (HBsAg) produced using recombinant DNA technology.
• Human Papillomavirus (HPV) Vaccine: Contains proteins from the HPV virus, specifically the L1 protein, which forms virus-like particles (VLPs) that stimulate an immune response.
• Impact: Provides effective immunity against the target pathogens with minimal risk of side effects.
• Polysaccharide Subunit Vaccines: Contain polysaccharide molecules from the surface of bacteria.

Examples:-

• Pneumococcal Polysaccharide Vaccine (PPSV23): Contains polysaccharides from 23 types of Streptococcus pneumoniae bacteria.
• Meningococcal Polysaccharide Vaccine: Contains polysaccharides from the Neisseria meningitidis bacteria.
• Impact: Effective in protecting against specific bacterial infections, though they may be less effective in young children.

Steps in subunit vaccine design:

1. Pathogen identification: Select the target pathogen and identify its key components.
2. Antigen identification: Determine the specific antigens (subunits) that elicit an immune response.
3. Antigen characterization: Study the structure, function, and immunogenicity of the selected antigens.
4. Expression and purification: Produce and purify the antigens using recombinant DNA technology or other methods.
5. Adjuvant selection: Choose an adjuvant to enhance the immune response.
6.  Formulation: Combine the antigen and adjuvant into a vaccine formulation.
7.  Immunogenicity testing: Evaluate the vaccine's ability to induce an immune response.
8. Safety and efficacy testing: Conduct preclinical and clinical trials to ensure safety and efficacy.
9. Regulatory approval: Obtain regulatory approval for vaccine use.

EXAMPLES

1. Protein-based vaccines (e.g., Hib, HepB)
2. Peptide-based vaccines (e.g., cancer vaccines)
3. Polysaccharide-based vaccines (e.g., pneumococcal conjugate vaccines)
4. Conjugate vaccines (e.g., meningococcal conjugate vaccines)
5. Virus-like particle (VLP) vaccines (e.g., HPV, HepB)

TOXOID VACCINE

• Toxoid Vaccines are designed to protect against diseases caused by bacterial toxins rather than the bacteria itself.
• Toxoids are vaccines which consist of exotoxins / toxins that have been inactivated, either by heat or chemicals produced by bacteria, which stimulate an immune response without causing disease.

•       Some examples are botulinum antitoxin and diphtheria antitoxin.

•     How Toxoid Vaccines Work:

       Inactivation of Toxin:

• Bacteria produce toxins that cause disease symptoms. In toxoid vaccines, these toxins are chemically or heat-inactivated to render them harmless.
• The inactivated toxins (toxoids) are used as the antigen in the vaccine

 Immune Response:

• The immune system recognizes the toxoid as a foreign substance and mounts an immune response.
• This response includes the production of antibodies specifically targeting the toxin.

Protection:

• If exposed to the actual toxin in the future, the immune system can quickly recognize and neutralize it, preventing disease.

STEPS IN TOXOID VACCINE DESIGN:

1. Toxin identification: Select the target toxin produced by the bacterium.
2. Toxin purification: Purify the toxin from bacterial cultures.
3. Toxoid preparation: Inactivate or modify the toxin to create a toxoid:

• Formaldehyde treatment
• Glutaraldehyde treatment
• Genetic modification
• Chemical modification

1. Immunogenicity testing: Evaluate the toxoid's ability to induce an immune response.
2.  Adjuvant selection: Choose an adjuvant to enhance the immune response.
3. Formulation: Combine the toxoid and adjuvant into a vaccine formulation.
4.  Safety and efficacy testing: Conduct preclinical and clinical trials to ensure safety and efficacy.
5. Regulatory approval: Obtain regulatory approval for vaccine use.

 TOXOID VACCINE TYPES:

1. Diphtheria toxoid (DT)
2. Tetanus toxoid (TT)
3. Pertussis toxoid (PT)
4. Botulinum toxoid
5. Clostridium perfringens toxoid

  ADVANTAGES OF TOXOIDS:

• Safety: The toxoid is inactivated, so there is no risk of causing the disease.
• Effective: Provides effective protection against diseases caused by bacterial toxins.
• Long-term Immunity: Generally, provides long-lasting immunity with a series of initial doses and periodic boosters.

DISADVANTAGES OF TOXOIDS:

• Booster Requirements: Toxoid vaccines often require booster doses to maintain immunity over time.
• No Protection Against Bacteria: They do not provide protection against the bacteria itself, only against the toxin it produces.

       

CONJUGATE VACCINES:

• Conjugate vaccine design involves combining a weakened or inactive pathogen (e.g., bacterial capsular polysaccharide) with a carrier protein to enhance immune response and provide protection against infectious diseases.

Types of conjugate vaccines:

1. Glycoconjugate vaccines (e.g., pneumococcal, meningococcal)
2. Protein-polysaccharide conjugates (e.g., Hib, HepB)
3. Viral conjugates (e.g., HPV, influenza)

Examples:

• Haemophilus influenzae type b (Hib) Vaccine: Conjugates polysaccharide from Hib bacteria with a protein carrier.
• Pneumococcal Conjugate Vaccine (PCV): Conjugates polysaccharides from Streptococcus pneumoniae with a protein carrier.
• Impact: Improves immune response in young children and provides longer-lasting protection.

Advantages:

• Safety: Lower risk of causing disease as they contain only parts of the pathogen.
• Specificity: Can target specific components of the pathogen, potentially reducing adverse effects.
• Suitable for Sensitive Groups: Safe for use in individuals with weakened immune systems.

Disadvantages:

• May require multiple doses or boosters to achieve and maintain immunity.
• Limited Immune Response: May not induce as robust an immune response as live attenuated vaccines.

STEPS IN PRODUCTION OF CONJUGATE VACCINE

• Chose the pathogen: Specific bacteria or virus that is wanted is selected to protect against.
• Pick the Polysaccharide: A key sugar molecule from the pathogen that will help trigger an immune response is identified.
• Select a Carrier Protein: A protein that will help the immune system recognize and respond to the polysaccharide is chosen. Common options are proteins from tetanus or diphtheria vaccines.
•  Link Polysaccharide and Protein: Decide on a method to attach the polysaccharide to the carrier protein. This can be done chemically, genetically, or enzymatically.
•  Optimize the Conjugate: Adjust the structure and ratio of the polysaccharide and protein to improve the vaccine’s effectiveness.
• Test Immunogenicity: Working of vaccine in animal models to gauge its potential effectiveness is checked.
• Choose an Adjuvant: If needed, select an adjuvant to enhance the immune response to the vaccine.
•  Formulate the Vaccine: Combine all the components into a final vaccine formulation that is stable and effective
•  Conduct Safety and Efficacy Trials: Perform extensive preclinical and clinical trials to ensure the vaccine is safe and works well in humans.
• Seek Regulatory Approval: Submit the vaccine for review by health authorities to ensure it meets all required safety and efficacy standards before it can be distributed.

SOME MODERN VACCINES AND THEIR PRODUCTION TECHNIQUES

 

PEPTIDE VACCINES:

• Peptide-based synthetic vaccines consist of 20–30 amino acid peptides that mimic specific epitopes of pathogens. These vaccines are designed to trigger strong immune responses by focusing on immunologically accessible regions of the pathogen. They are typically subunit vaccines, using purified antigens and often administered with adjuvants.

Key points about peptide vaccines include:

• Peptide Composition: They use short, synthesized peptides representing specific epitopes of an antigen.
• Targeted Design: Only immunologically accessible peptides on the pathogen's surface are used.
• Production Advantages: Peptide vaccines are stable, cost-effective, and easier to manufacture.

Immunogenicity: They are highly immunogenic when combined with T-cell epitopes provided by carrier proteins or other adjuvants.

• Examples of peptide vaccines: -Influenza (injection), Haemophilus influenzae type b (Hib), Pertussis Human papillomavirus (HPV).

•  Steps involved in the preparation of PEPTIDE vaccines

• Peptide Bond Synthesis: The peptide bonds are made using a method called Solid Phase Peptide Synthesis (SPPS), invented by Robert Bruce Merrifield. This method uses solid materials like polystyrene beads to build the peptide chains through a series of chemical reactions.
• Characterization: To ensure the peptide is correct and pure, scientists use techniques like NMR (Nuclear Magnetic Resonance) and HPLC (High-Performance Liquid Chromatography) to check the sequence and look for impurities.
• Carriers: Different carriers might be used in the vaccine based on its composition. Carriers help deliver the vaccine effectively.
• Adjuvants: Some vaccines include adjuvants, which enhance the immune response. These can be small amounts of substances like aluminum salts, which are safe and help the vaccine work better. Previously aluminium salts were used but in recent years, two
• new adjuvants have been licensed for use in human vaccines. One, MF59, is an oil-in- water emulsion like alum, believed to aid in slow antigen delivery. The other, AS04, contains alum plus a TLR4 agonist. TLR4 is a PRP for bacterial lipopolysaccharides (LPS), and signaling by this adjuvant ultimately encourages TH1 responses. All of these adjuvants have been found to enhance the production of antibodies as compared to unadjuvanted vaccine preparations.

• Stabilizers: Stabilizers keep the vaccine components from reacting with each other or sticking to the vial. They can be sugars (like lactose), amino acids (like glycine), or proteins (like recombinant human albumin).

Advantages: -

• Simple Production: Peptides are easy to produce, reproduce, and are cost-effective.
• Chemical Synthesis: Eliminates issues related to biological contamination.
• Stability: Peptides are water-soluble, stable at room temperature, can be freeze-dried, and are easy to store without a cold chain.
• Versatility: Peptide vaccines can be designed to target different parts of a pathogen or multiple strains of a pathogen at once. They can also be used to protect against different kinds of pathogens by including several pieces of the pathogen in one vaccine. This makes them flexible and useful for a wide range of diseases.
• Quality Control: Production and quality control processes are simpler.
• Safety: Lower toxicity, safer, and free from risk of infection as no pathogens are involved.

Disadvantages: -

• Several doses must be given for proper -life.
• Requires adjuvant.
• Duration of immunity is shorter
• Carriers used in vaccine production may cause hypersensitivity reaction.
• Requires primary coarse of infection followed by boosters.

RECOMBINANT VACCINE

• Recombinant vaccines are made using a technology called recombinant DNA technology.
• They are created by:
• Gene Insertion: Scientists insert the gene for a specific antigen (like a bacterial surface protein) into bacterial or mammalian cells.
• Protein Production: These cells then produce the antigen, which is the part of the pathogen that triggers an immune response.
• Purification: The antigen is then extracted and purified from the cells.
• Plasmid DNA: For some vaccines, plasmid DNA is used. This DNA is copied in bacteria (like E. coli), and the resulting product is purified for use in the vaccine.
• The first recombinant vaccine approved for use in people was the hepatitis B vaccine. It was made by cloning the gene for a key hepatitis B virus protein and expressing it in yeast cells.

DNA VACCINES:

• DNA vaccination is a technique for protecting an organism against disease by injecting it with genetically engineered DNA to produce an immunological response.

 How it works:

•  Injection: DNA that codes for specific proteins from a pathogen is injected into cells.
•  Protein Production: The cells use this DNA to make the pathogen’s proteins.
•  Immune Response: These proteins are recognized as foreign by the immune system. The immune system then reacts to these proteins, helping to protect against the disease.
• DNA vaccines are a safer option compared to traditional live or inactivated vaccines for both humans and animals.

Delivery method of DNA vaccines: -

•  Nasal spray
•  Intramuscular injection
•  Intravenous injection
•  Intradermal injection
•  Gene gun delivery

Advantages of DNA Vaccine

• Focused Immune Response: DNA vaccines target the antigen of interest, leading to a specific immune response.
• Cost-Effective: They are relatively inexpensive to produce.
• Low Infection Risk: There's minimal risk of infection compared to traditional vaccines.
• Effective Antigen Presentation: They promote antigen presentation via MHC class I and II molecules.
• Long-Term Immunogen Persistence: They offer durable immune responses.
• Rapid Production: Large quantities of DNA can be produced quickly and at low cost.
• Stability and Storage: DNA vaccines are stable, do not require refrigeration, and are easier to transport and store.
• Safety in Production: They pose less risk to manufacturers as they do not involve live pathogens.

Limitations of DNA Vaccine

• Risk of affecting genes controlling cell growth
• Possibility of tolerance to the antigen
• Potential for atypical processing of bacterial and parasite proteins
• Limited to protein immunogens

Applications of DNA Vaccine

• DNA vaccines against cancer – Cancer have been a cause of death for many worldwide.
• DNA vaccines are reliable forms of immunotherapy and can be effective for people fighting cancer
• DNA vaccines against tuberculosis – DNA-based vaccine can be used to curb Tuberculosis which is a major health problem for people across the world
• DNA vaccines against HIV – Human immunodeficiency virus (HIV) cause acquired immunodeficiency syndrome (AIDS) which is a health crisis and using this type of vaccine, can be treated.

Steps for DNA Vaccine Preparation:

• Cut open the circular DNA vectors and trim the ends of copied genes using restriction enzymes.
• Insert the trimmed genes into the opened vectors.
• Allow the vectors to close, forming loops with the new genes inside.
• Introduce these altered vectors into bacteria.
•  Grow the bacteria in suitable conditions, allowing them to replicate and produce many copies of the vector/gene loops.
• After producing many copies, use a purifier to separate the vectors as they grow.
• Use a detergent to break open the bacteria, releasing the DNA.
• Separate the smaller vector DNA loops from the larger bacterial DNA.
•  Purify the vector DNA to obtain the final vaccine product.
• Load the purified DNA vaccine into syringes for administration.
• When injected, a small percentage of these vectors enter the nuclei of body cells and start working to produce an immune response.
• This process creates numerous copies of DNA vectors containing the desired gene, which can then be used as a vaccine.

MESSENGER RNA (mRNA) VACCINES

•  One of the newest and most exciting areas in vaccine technology is the use of mRNA vaccines. Unlike conventional vaccines—which can take many months or even years to cultivate—mRNA vaccines can be developed quickly using the pathogen’s genetic code.
• When an mRNA vaccine is delivered, the RNA material teaches our body how to make a specific type of protein that is unique to the virus, but does not make the person sick. The protein (typically a component of the pathogen) triggers an immune response, which includes the generation of antibodies that recognize the protein. That way, if a person is ever exposed to that virus in the future, the body would like have the tools (antibodies) to fight against it.

 STEPS OF PFIZER-BIONTECH (COVID) VACCINE

• The genetic sequence of the viral spike protein is copied.
• From it an optimized mRNA sequence is created to be used for vaccine formulation.
• mRNA vaccine is encapsulated in lipid nanoparticle.
• Vaccine is injected into arm muscle.
• The lipid nanoparticle encounters a cell in the body.
• The lipid nanoparticle releases mRNA into the cell. The mRNA does not enter the nucleus of the cell.
• The instructions carried by the mRNA vaccine are used by the cell to produce spike proteins.
• Spike proteins are expressed on the cell's surface to be detected by immune system and create antibodies against.

Benefits:

• It is a very powerful technique to be able to create a lot of a vaccine fast. The benefit is that the technology is very adaptable.
• We can potentially go in and change the mRNA in the formulation to target a new antigen and can make a lot of high-quality vaccine material relatively quickly.

 Examples: Pfizer-BioNTech COVID-19 vaccine

VIRAL VECTOR VACCINES

•  Vector Vaccines use a harmless virus (the vector) to deliver genetic material from a pathogen into cells. This genetic material instructs cells to produce a protein from the pathogen, which then triggers an immune response.

 How Vector Vaccines Work:

• Vector Virus Selection: A harmless virus (vector), such as an adenovirus, is chosen and modified to carry genetic material encoding a pathogen protein (e.g., SARS-CoV-2 spike protein).

❖   Introduction: The modified vector virus is injected into the body.

• Protein Production: The virus enters cells, which then use the genetic material to produce the pathogen protein, displaying it on their surface.
• Immune Response: The immune system detects the foreign protein, leading to the production of antibodies and activation of T-cells to combat the pathogen
• Benefits: Viral vector vaccines usually trigger a strong immune response. Typically, only one dose of the shot is needed to develop immunity. Boosters may be needed to maintain immunity.
• Examples: Ebola vaccine, COVID-19 vaccine (AstraZeneca and Johnson & Johnson)

VACCINE DEVELOPMENT

• Vaccine development is a lengthy and complex process, typically taking 12 to 15 years, and involves several key phases:
• Pre-Clinical Trials: Researchers identify potential vaccine candidates and test them in vitro and in vivo to assess safety and effectiveness before human trials begin.
• Phase I Clinical Trials: Conducted with 20-50 healthy volunteers to evaluate safety, dosage, and side effects. This phase lasts 12 to 18 months.
• Phase II Clinical Trials: The vaccine is tested on 100-300 people to further assess safety and immunogenicity, refine dosage and scheduling. This phase can last over 2 years.
• Phase III Clinical Trials: Involving 3,000 to 50,000 subjects, this phase tests the vaccine’s safety and efficacy on a large scale and examines its interaction with other vaccines. It lasts 3 to 5 years.
• Phase IV or Pharmacovigilance: After the vaccine is licensed, ongoing monitoring ensures continued safety and effectiveness, and long-term follow-up trials are conducted to confirm sustained protection.

HOW THE VACCINE WORKS

• Vaccines work by introducing a small, harmless piece of a virus or bacteria, known as an antigen, to the body. This triggers the immune system to produce antibodies and immune cells that can recognize and fight the specific pathogen.

Mechanism of vaccines:

• Introduction of antigen: The vaccine contains a weakened or killed form of the virus or bacteria, or a small portion of its genetic material (antigen).
• Recognition by immune cells: The antigen is recognized by immune cells, such as dendritic cells and macrophages, which engulf and process it.
• Activation of immune response: The processed antigen is presented to T-cells (a type of immune cell) by the immune cells, activating an immune response.
• Production of antibodies: B-cells (another type of immune cell) produce antibodies that specifically target the antigen.
• Memory cell formation: Some immune cells become memory cells, which remember the specific pathogen and can quickly respond if exposed again in the future.
• Immune system preparedness: The immune system is now prepared to recognize and fight the specific pathogen if exposed again, providing immunity.

HERD IMMUNITY

• Vaccines also work on a community level. Some people can't be vaccinated, either because they are too young, or because their immune systems are too weak, according to the CDC. But if everyone around them is vaccinated, unvaccinated people are protected by something called herd immunity.

NEW VACCINES IN DEVELOPMENT

• Recent advances in vaccine design development use new technologies like genomics, proteomics, and synthetic chemistry instead of just traditional methods. This has enabled the rational design and large-scale production of vaccines using engineered proteins and optimized antigens.

Future Directions in Vaccine Designing Development:

• Universal Vaccines: Designed to provide broad protection against multiple strains or variants of a pathogen, such as universal influenza or coronavirus vaccines, and even cancer vaccines.
• Global Vaccination Strategies: Focus on improving the effectiveness, reach, and equity of vaccination programs worldwide, addressing challenges in accessibility, distribution, and integration.
• Personalized Vaccines: Tailored to individual genetic profiles and specific health conditions to offer more precise and effective immunization.

THREE KEY BREAKTHROUGH APPROACHES

• Firstly, genomic sciences gave birth to the field of reverse vaccinology, which has enabled the rapid computational identification of potential vaccine antigens.
• Secondly, major advances in structural biology, experimental epitope mapping, and computational epitope prediction have yielded molecular insights into the immunogenic determinants (epitope) defining protective antigens, enabling their rational optimization.
• Thirdly, and most recently, computational approaches have been used to convert this wealth of structural and immunological information into the design of improved vaccine antigens.

CHALLENGES IN VACCINE DESIGNING

• Many pathogens, like influenza and HIV, mutate rapidly, making it difficult to design vaccines that remain effective over time.
• Different individuals or populations may respond differently to the same vaccine, influenced by genetics, age, health status, and prior exposure to the pathogen.
• Finding safe and effective adjuvants (substances that enhance the immune response) is crucial but challenging. Ensuring vaccines are available, affordable, and accessible worldwide, including in low- resource settings.

CONCLUSIONS

• Vaccine can be designed and developed in a number of ways depending on the need and requirement. Advancements in molecular biology, genetic engineering, and computational modeling have revolutionized vaccine design, allowing for more precise targeting of pathogens.
• However, vaccine development faces a number of challenges, such as overcoming the limited effectiveness of a number of vaccines, the need for frequent vaccine reformulation, as well as a complete lack of vaccines for some diseases.
• A central goal of vaccination is to generate long lasting and broadly protective immunity against target pathogens, but this goal is hampered by the variability of both the target pathogens and the human immune system.

REFERENCES

• Kuby Immunology 7th Edition
• Microbiology by Prescott
• Microbiology and Immunology 2nd Edition by Shubash Chandra Parija
• https://www.niaid.nih.gov/research/vaccine-types