Vaccines and Immunization

• Immunization provides specific protection against common and dangerous pathogens
• Specific acquired immunity can occur naturally through mother or infection or it can be artificially acquired through antiserum or vaccines
• Vaccines are biological preparations that provide active and acquired specific immunity to a disease
• The protective immunity from a vaccine could be lifelong, like in MMR, or short-term, like in cholera where it lasts six months
• There are three main approaches to making a vaccine: using a whole virus or bacterium, using parts that trigger the immune system, or using just the genetic material

Types of Vaccines

• There are nine types of vaccines: inactivated, attenuated, subunit, conjugate, toxoid, peptide, viral vector, recombinant, and DNA vaccines

Inactivated (Killed) Vaccines

• Inactivated vaccines use organisms inactivated by heat, chemicals, or UV irradiation
• Examples are the Salk polio, typhoid, and cholera vaccines
• Advantages include being used safely because they are inactivated
• Advantages include stimulating immunity to antigens in their natural conformation
• Disadvantages include needing a large number of organisms to stimulate immunity,
• Disadvantages include requiring periodic boosters to maintain immunity
• Inactivated vaccines only induce humoral immunity
• Inactivated vaccines are costly to administer

Attenuated (Weakened) Vaccines

• To make attenuated vaccines, the pathogen is grown in animals or tissue culture under conditions that make it less virulent
• An example includes the Sabin oral polio vaccine-measles, mumps, and rubella vaccines
• Infectious organisms can stimulate the generation of memory cellular and humoral immune responses
• Less of the vaccine is needed to induce protection since the pathogen can multiply in the host
• Whole pathogens stimulate responses to antigens in their natural conformation
• Attenuated vaccines can be administered orally, which is less expensive than injections
• Oral administration induces mucosal immunity and IgA synthesis which gives the body more protection
• Disadvantages include organisms reverting to their virulent form and causing disease and may cause hypersensitivity

Subunit Vaccines

• Subunit vaccines contain purified antigens rather than whole organisms
• Subunit vaccines are not infectious, so they can safely be given to immunosuppressed patients
• There is a less likely chance of unfavorable immune reactions
• Antigens may not retain their native conformation, so antibodies produced against the subunit may not recognize the same protein on other pathogens
• Isolated protein does not stimulate the immune system as well as a whole organism vaccine
• Adjuvants increase the effectiveness of subunit vaccines, and an adjuvant slows down antigen release for a more sustained immune stimulation
• Alum (aluminum salts) is a common adjuvant that aggregates proteins to make them easier for phagocytes to engulf
• Pertussis toxin, a component of the acellular DPT vaccine, acts as an adjuvant
• Some bacterial components may cause too much inflammation to be safe for humans

Conjugate Vaccines

• Conjugate vaccines combine a weak antigen with a strong antigen as a carrier
• Conjugate vaccines have been developed for pathogens whose polysaccharide capsules protect from phagocytosis
• Examples of pathogens include Haemophilus influenzae B (HiB), Streptococcus pneumoniae and Neisseria meningitidis
• Immunity to these organisms requires opsonizing antibodies but infants make poor T-independent responses to polysaccharide antigens
• By linking the polysaccharides to protein carriers, they are converted into T-dependent antigens and protective immunity is induced

Toxoid Vaccines

• Toxoid vaccines are made from toxins produced by bacteria (e.g., tetanus or diphtheria toxoids)
• Toxins are treated to eliminate their toxicity using chemicals or heat, but they remain antigenic
• Toxoid vaccines are able to induce antibodies that can neutralize the native toxins
• The diphtheria and tetanus toxoid components of DPT are examples

Peptide Vaccines

• Peptide vaccines are synthetic peptides that are highly immunogenic and stimulate the desired immune response
• These peptides are made to minimize the side effects of traditional vaccines
• The disadvantage of peptide vaccines is that they may not induce protective immunity for all individuals

Viral Vector Vaccines

• Viral vector vaccines are a newer technology that uses harmless viruses to deliver the genetic code of target vaccine antigens to cells
• Cells produce protein antigens that express protein on the surface of cells to stimulate an immune response, creating antibodies and defensive white blood cells
• If the person later becomes infected with the organism, the antibodies will fight it
• Viral vectored vaccines are significantly cheaper to produce compared with subunit vaccines

Recombinant Vaccines

• Recombinant vaccines are produced through recombinant DNA technology
• DNA encoding an antigen is inserted that stimulates the immune response into bacterial or yeast cells
• Advantages of recombinant vaccines include use in antigens that do not elicit protective immunity or antigens which elicit damaging responses
• Advantages of recombinant vaccines include the eliminated antigens that elicit damaging responses from the vaccine
• Recombinant vaccines uses proteins whose expressed have their native conformation
• Disadvantages include the high cost since the genes for the desired antigens must be located, cloned, and expressed efficiently
• The Hepatitis B virus (HBV) vaccine, a recombinant subunit vaccine, is the only recombinant vaccine currently in use for humans
• Hepatitis B surface antigen is produced from a gene transfected into yeast cells and purified for injection as a subunit vaccine
• Recombinant vaccines are much safer than using attenuated HBV, which could cause lethal hepatitis or liver cancer if it reverted to its virulent phenotype

DNA Vaccines

• DNA vaccines are some of the newest vaccines and they are very effective and safe
• Like recombinant vaccines, the genes for desired antigens are located and cloned
• DNA is injected into the muscle using a "gene gun" that uses compressed gas to blow the DNA into the muscle cells
• Muscle cells express the pathogen DNA to stimulate the immune system.
• They are very effective and safe
• Both humoral and cellular immunity have been induced by DNA vaccines

COVID-19 Vaccines

• There are four different types of COVID-19 vaccines which include: Whole virus vaccine, Viral subunit vaccine, Viral vector vaccine, and Nucleic acid vaccine

Whole Virus COVID-19 Vaccine

• Inactivated vaccine examples include: Sinovac (CoronaVac vaccine), Sinopharm
• Live attenuated vaccines examples include COVI-VAC which is a single-dose, intranasal, live attenuated vaccine against COVID-19 and generated by Codagenix

Subunit COVID-19 Vaccines

• Protein subunit vaccines only include parts of a virus that stimulate the immune system
• A protein subunit vaccine contains harmless S proteins
• Novavax is working on a protein subunit COVID-19 vaccine

Viral Vector COVID-19 Vaccines

• These vaccines can't cause infection from COVID-19 or from the viral vector virus
• The genetic material doesn't become part of DNA
• Examples include: The Janssen/ Johnson & Johnson COVID-19 vaccine and the AstraZeneca COVID-19 vaccine.

Nucleic Acid COVID-19 Vaccines

• Messenger RNA (mRNA) vaccines are genetically engineered from mRNA to give the cells instructions to make the S protein, found on the surface of the COVID-19 virus
• After vaccination, cells make the S protein pieces and display them on cell surfaces, causing the body to create antibodies
• Both the Pfizer-BioNTech and the Moderna COVID-19 vaccines use mRNA and mRNA is broken down immediately and never enters the nucleus of cells, where DNA is kept

Case Studies

• A 30 years old pregnant female came to the clinic seeking covid-19 vaccine
  • Advice is needed regarding appropriate vaccination recommendations
• 35 years old surgeon exposes to needle stick injury during surgery and seeks consultation due to the patient being HBV positive
  • Recommendation suggestions are needed regarding positive HBV results
• Determining importance of adding adjuvant to vaccines