vaccine Flashcards
What is an ideal vaccine?
- to produce the same immune protection which usually follows natural infection but w/o causing disease
- to generate long-lasting immunity
- to interrupt spread of infection
Immunization: the deliberate provocation of an 1._______ immune response by introducing 2. _______ in the body.
It’s a procedure designed to increase concentrations of 3. _______ and/or 4.________ which are reactive against infection.
- adaptive
- antigen
- antibodies
- effector T cells
Describe the 2 types of immunization
Passive immunity: protection is immediate
Active immunity: takes time (usually several weeks) to develop.
Describe passive immunity:
- Natural
- Artificial
- Natural: transplacental (mother to child) lg G
2. Artificial: injection of preformed antibodies
Advantages & disadvantages of passive immunity
Adv:
- immediate protection
- can be used in immunosuppressed
Disadv:
- short period of protection
- potential allergic response if foreign antibodies given
Desc. active immunity:
- Natural:
- Artificial:
- Natural: following infections (immune to re-infection)
2. Artificial: vaccination– ensure large no. of antibodies & lymphocytes are avail before exposure to pathogen
Does smallpox only occur in humans?
Yes
Does smallpox cause a latent or persistent infection?
No
How was the eradication of smallpox possible?
- smallpox vaccine was effective against all strains of variola virus
- high fidelity DNA polymerase, variola viruses were unable to undergo antigenic variation to escape immunity
- CD4 T cell-dependent neutralising antibodies to vaccinia antigens (pox virus family) are cross-reactive with smallpox antigens
Features of effective vaccines
- safe
- protective
- gives sustained protection (must last for several years)
- induces neutralising antibody (prevent infection)
- induced protective t cells
- practical considerations: low cost per dose, few side effects, etc
Selective vaccination for those at increased risk of disease:
- hep B
- influenza
- yellow fever
- rabies
- meningitis
- hep A
- measles
- strep. pneumonae
What is herd immunity?
Herd immunity occurs when a large portion of a community (the herd) becomes immune to a disease, making the spread of disease from person to person unlikely. As a result, the whole community becomes protected — not just those who are immune.
To achieve herd immunity, the % of individuals who need to be vaccinated depends on _____________________
the disease and the vaccines used.
Herd immunity is only valid for _____________
transmissible infectious diseases eg. flu
Why is herd immunity important?
- no vaccine is 100% effective
- immunocompromised people are unable to receive live vaccines
What do vaccines generally contain?
And describe them.
- Antigen(s) : any protein, peptide, substance, etc that stimulates an immune response (SPECIFIC to the pathogen of interest)
- Adjuvant : a substance that enhances the immune response to a weakly immunogenic antigen (non-specific). It can also allow slow release of antigen to allow time for memory response to form
Desc inactivated (killed) vaccines
- inactivation through heat or chemical fixation
- need multiple injections in initial course
- usually need boosters
- may be toxic
- need for adjuvant
- poor cell mediated immunity
Examples of inactivated (killed) vaccines
cholera plague influenza rabies polio (salk)
Desc live (attenuated) vaccines
They contain virulent human viruses that has been weakened.
Examples of live (attenuated) vaccines
polio (oral vaccine) mumps measles rubella yellow fever chickenpox typhoid
Advantages of live (attenuated) vaccines
- mimic natural infection
- produce large antigenic stimulus (organism can still replicate)
- generally induce T & B lymphocytes responses
- provide long-lasting protection
Disadvantages of live (attenuated) vaccines
- may retain some pathogenicity
- may revert to virulence
- may not be safe to vaccinate the immunocompromised
- require a good cold chain
Desc inactivated exotoxins (toxoid)
- inactivated by heat or chemicals
- intended to build immunity against the toxins & not the bacteria that produce the toxins
Examples of inactivated exotoxins (toxoid)
tetanus toxoid
diphtheria toxoid
What vaccine is most effective for those <2y.o. particularly vulnerable to bacterial meningitis?
conjugate vaccine
Examples of conjugate vaccine
polysaccharides from Pneumococcus & meningococcal capsules
Do polysaccharides from Pneumococcus have low levels of lg M?
Yes
Do polysaccharides from Pneumococcus have memory?
No
Desc subunit vaccines
- they present 1 or more antigens to the immune system w/o introducing pathogen particles
- “subunit”: antigen is a fragment of the pathogen
The 2 methods of subunit vaccines
- Present an antigen to the immune system using a specific, isolated protein from the pathogen
- Put an antigen’s gene from the targeted virus into another virus, to make a recombinant virus. The recombinant vector will express the antigen which is extracted.
Example of a subunit vaccine
hep. B vaccine (yeast vector)
Advantages of subunit vaccine
- cannot revert back to virulence
- safe for the immunocompromised
- can withstand changes in conditions (eg. temp., light exposure, humidity)
Disadvantages of subunit vaccine
- reduced immunogenicity compared to attenuated vaccines
- require adjuvants to improve immunogenicity
- often require multiple doses/ boosters to provide long-term immunity
- q costly
- can be difficult to isolate the specific antigen
RNA vaccine:
uses a copy of the mRNA that codes for the antigen of interest to produce an immune response
3 types of RNA vaccine
- non-replicating mRNA (mRNA encoding antigen + liposome)
- in VIVO self-replicating mRNA (mRNA encoding antigen + the viral RNA replication machinery)
- in VITRO dendritic cell non-replication mRNA
Advantages of RNA vaccine
- Safety
- RNA vaccines are not made with pathogen particles of inactivated pathogen, so are non-infectious
- RNA does not integrate itself into the host genome
- RNA strand in the vaccine is degraded once the protein is made - Production: vaccines can be produced more rapidly in the lab
Disadvantages of RNA vaccine + strategies to tackle them
- May elicit an unintended immune rxn
- strategy: to minimise, the mRNA vaccine sequences are designed to mimic those produced by mammalian cells - Delivery: free RNA in the body is quickly degraded
- strategy: the RNA strand is incorporated into a larger molecule to help stabilise it or package into particles/lipsomes - Storage: need to be frozen or refridgerated
