MCB 404 Medical Virology - Viral Vaccines PDF

AMBROSE ALLI UNIVERSITY, EKPOMA MICROBIOLOGY DEPARTMENT MCB 404: MEDICAL VIROLOGY VIRAL VACCINES Viral vaccines is a biological preparation that provides active acquired immunity to a particular infectious or malignant di...

AMBROSE ALLI UNIVERSITY, EKPOMA MICROBIOLOGY DEPARTMENT MCB 404: MEDICAL VIROLOGY VIRAL VACCINES Viral vaccines is a biological preparation that provides active acquired immunity to a particular infectious or malignant disease. Viral vaccines contain either inactivated viruses or attenuated (alive but not capable of causing disease) viruses or protein parts of the virus 1. LIVE ATTENUATED VIRUS VACCINES Attenuated vaccine is created by reducing the virulence of a pathogen, but still keeping it viable (or "live"). Attenuated vaccines are “weakened” version of pathogens (virus or bacteria). They are modified so that it cannot cause harm or disease in the body but are still able to activate the immune system. Attenuation takes an infectious agent and alters it so that it becomes harmless or less virulent (avirulent). Live vaccines are derived from “wild” viruses. These wild viruses are attenuated (weakened) in a laboratory, usually by repeated serial passage using tissue culture media. For example, the measles virus used as a vaccine today was isolated from a child with measles disease in 1954. Almost 10 years of serial passage using tissue culture media were required to transform the wild virus into the attenuated vaccine virus. When a live, attenuated vaccine does cause disease, it is usually much milder than the natural disease and is considered an adverse reaction to the vaccine. The immune response to a live, attenuated vaccine is virtually identical to that produced by a natural infection because the immune system does not differentiate between infections with a weakened vaccine virus and an infection with a wild virus. Live, attenuated vaccines are fragile and can be damaged or destroyed by heat and light. They must be stored and handled carefully. Attenuated vaccines stimulate a strong and effective immune response that is long-lasting. Attenuated vaccines produce a stronger and more durable immune response with a quick immunity onset. They are generally avoided in patients with severe immunodeficiencies. Attenuated vaccines function by encouraging the body to create antibodies and memory immune cells in response to the specific pathogen which the vaccine 1  protects against. Common examples of live attenuated vaccines are measles, mumps, rubella, yellow fever, and some influenza vaccines. This type of vaccine works by activating both the cellular and humoral immune responses of the adaptive immune system. Viral Vaccine Safety Live-attenuated vaccines are safe and stimulate a strong and effective immune response that is long-lasting. Given Viruses are attenuated, it is extremely rare for virus to revert to their pathogenic form and subsequently cause disease. Additionally, within the four WHO- recommended live attenuated viral vaccines (oral polio, measles, rotavirus, and yellow fever), severe adverse reactions are extremely rare. Individuals with severely compromised immune systems (e.g., HIV-infection, chemotherapy, immunosuppressive therapy, leukemia, combined immunodeficiencies) typically should not receive live-attenuated vaccines as they may not be able to produce an adequate and safe immune response. Household contacts of immunodeficient individuals are still able to receive most attenuated vaccines since there is no increased risk of infection transmission. As precaution, live-attenuated vaccines are not typically administered during pregnancy. This is due to the risk of transmission of virus between mother and fetus In particular, the varicella and yellow fever vaccines have been shown to have adverse effects on fetuses and nursing babies. Polio vaccine. Rotavirus vaccine, Rubella vaccine, Smallpox vaccine.Varicella vaccine, Live attenuated influenza vaccine Advantages 1. Accurately imitate natural infections. 2. Are effective at evoking both strong antibody and cell-mediated immune reactions. 3. Can elicit long-lasting or life-long immunity. 4. Often only one or two doses are required. 5. Quick immunity onset. 6. Cost-effective (compared to some other health interventions). 7. Can have strong beneficial non-specific effects. 2 Disadvantages 1. In rare cases, natural mutations during viral replication, or interference by related viruses, can cause an attenuated virus to revert to its wild-type form or mutate to a new strain, potentially resulting in the new virus being infectious or pathogenic. 2. Often not recommended for severely immunocompromised patients due to the risk of potential complications. 3. Live strains typically require advanced maintenance, such as refrigeration and fresh media, making transport to remote areas difficult and costly. 2. INACTIVATED OR KILLED VIRAL VACCINE An inactivated vaccine (or killed vaccine) is a vaccine consisting of virus particles, bacteria, or other pathogens that have been grown in culture and then killed to destroy disease- producing capacity. Pathogens for inactivated vaccines are grown under controlled conditions and are killed as a means to reduce infectivity and thus prevent infection from the vaccine. Attenuated vaccines are often preferable for generally healthy people because a single dose is often safe and very effective. However, some people cannot take attenuated vaccines because the pathogen poses too much risk for them (for example, elderly people or people with immunodeficiency). For those patients, an inactivated vaccine can provide protection. Inactivated vaccines exist for many viruses, including influenza, Polio (IPV), rabies, hepatitis A. The pathogen particles are destroyed and cannot divide. When manufactured correctly, the vaccine is not infectious, but improper inactivation can result in intact and infectious particles. Whole pathogen inactivated vaccines are produced when an entire pathogen is 'killed' using heat, chemicals, or radiation, although only formaldehyde and beta-Propiolactone exposure are widely used in human vaccines. Split virus vaccines are produced by using a detergent to disrupt the viral envelope. This technique is used in the development of many influenza vaccines. Advantages 3  1. Inactivated pathogens are more stable than live pathogens. Increased stability facilitates the storage and transport of inactivated vaccines. 2. Unlike live attenuated vaccines, inactivated vaccines cannot revert to a virulent form and cause disease. 3. Unlike live attenuated vaccines, inactivated vaccines do not replicate and are not contraindicated for immunocompromised individuals. 3. SUBUNIT VACCINES A subunit vaccine is a vaccine that contains purified parts of the viral pathogen that are antigenic, or necessary to elicit a protective immune response. Subunit vaccine can be made from disasembled viral particles in cell culture. A "subunit" viral vaccine doesn't contain the whole pathogen, unlike live attenuated or inactivated vaccine, but contains only the antigenic parts such as proteins, or peptides. Viral Subunit vaccines can be made one of two ways: from the original pathogen or recombinantly. Recombinant vaccines use another organism to make the vaccine antigen. Because the vaccine doesn't contain "live" components of the pathogen, there is no risk of introducing the disease, and is safer and more stable than vaccines containing whole pathogens. Other advantages include suitability for immunocompromised individuals. Disadvantages include being relatively complex to manufacture compared to some vaccines, and requiring time to examine which antigenic combinations may work best example are Coronavirus disease 2019, influenza, Herpes zoster. Type of subunit vaccines Protein subunit Protein-based vaccines allow you to make a protective response against a protein on the surface of a virus. A protein subunit is a polypeptide chain or protein molecule that assembles with other protein molecules to form a protein complex. Large assemblies of proteins such as viruses often use a small number of types of protein subunits as building blocks. A key step in creating a recombinant protein vaccine is the identification and isolation of a protein subunit from the viru which is likely to trigger a strong and effective immune response, without including the parts of the virus that enable the virus to reproduce. Parts of the protein shell or capsid of a virus are 4 often suitable. The goal is for the protein subunit to prime the immune system response by mimicking the appearance but not the action of the pathogen. Another protein-based approach involves self‐assembly of multiple protein subunits into a Virus-like particle (VLP) or nanoparticle. The purpose of increasing the vaccine's surface similarity to a whole virus particle (but not its ability to spread) is to trigger a stronger immune response. Protein-based vaccines for COVID-19 tend to target either its spike protein or its receptor binding domain. Advantages Subunit vaccines only contain pieces of a pathogen, not the whole organism, so they cannot make you sick or cause infection. This makes them suitable for people who should not receive “live” vaccines, such as young children, older people, and immunocompromised people. 4. VIRAL VECTOR VACCINES A viral vector vaccine is a vaccine that uses a viral vector to deliver genetic material (DNA) that can be transcribed by the recipient's host cells as mRNA coding for a desired protein, or antigen, to elicit an immune response. COVID-19 vaccines a Ebola vaccines. 5. mRNA VACCINE mRNA vaccines introduce a short-lived synthetically created fragment of the RNA sequence of a virus into the individual being vaccinated. These mRNA fragments are taken up by dendritic cells through phagocytosis. The dendritic cells use their internal machinery (ribosomes) to read the mRNA and produce the viral antigens that the mRNA encodes. The body degrades the mRNA fragments within a few days of introduction. Once the viral antigens are produced by the host cell, the normal adaptive immune system processes are followed. The mRNA is delivered by a co-formulation of the RNA encapsulated in lipid nanoparticles that protect the RNA strands and help their absorp tion into the cells. Advantages 5 mRNA vaccines are not constructed from an active pathogen (or even an inactivated pathogen), they are non-infectious. Disadvantages mRNA is fragile and must be kept at very low temperatures to avoid degrading and thus giving little effective immunity to the recipient. Some vaccine mRNA vaccine has to be kept between −80 and −60 °C (−112 and −76 °F) and some can be stored between −25 and −15 °C (−13 and 5 °F). 6