Micro chapter 45: Vaccines and Antisera for the Prevention and Treatment of Infectious Diseases
Active immunization – administration of all or part of a microorganism, or a modified product of that
organism, to cause an immune response mimicking infection, but with little to no risk to the patient
Vaccine – immunizing agent derived from microorganisms consisting of:
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Live, attenuated microorganisms
Killed microorganisms or parts of microorganisms
Killed whole agents
Extracts of microorganisms
Toxoid – inactivated bacterial toxin that is no longer toxic (can’t damage us) but still induces an antibody
response
Passive immunization – receiving exogenous antibodies to prevent disease
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Passive immunization can be given through the placenta, through colostrum (breast milk), or by
injection
Things you can use for passive immunization is IG through muscles, IG given by IV, human
plasma, and animal antibodies
Immune globulin (IG) – mixture of antibodies made from blood plasma
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Specific IG – antibodies made from plasma from people with high #’s antibodies to a specific
microorganism
Intravenous IG (IVIG) – used to treat immunodeficiencies, inflammatory conditions, and cancers
Attenuate – decrease in the virulence of a microorganism
Antigen – molecule recognized by the immune system
Herd immunity – immunity provided to the population when large #’s of the population are vaccinated
Benefits of a vaccine to society – herd immunity, and decrease in health care costs
No vaccine though is completely safe or effective, and they can have side effects
Active immunization with vaccines or toxoids leads to prolonged immunity, and is the preferred method,
as opposed to passive immunization (administering IG’s)
As a rule, antibody responses to killed vaccines or toxoids can take several weeks to develop, and often
need 2-3 doses at several week intervals to elicit an adequate and persistent immune response
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With live vaccines, most people will develop protective immunity within 2 weeks
To maintain protective antibody concentrations over a lifetime, many vaccines must be readministered
as booster doses
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Ex: booster doses of tetanus and diphtheria toxoids should be given every 5-10 years
Since most infectious disease have short incubation periods (usually less than 2 weeks), active
immunization is often ineffective after exposure
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Sometimes, passive immunization with specific globulins or antitoxins can be used after
exposure
Antibody-containing stuff can inhibit the immune response elicited by a vaccine, so you wait to give a
live vaccine until passive immunity has gone away, usually about 11 months
You use both passive and active immunization together for diseases with long incubation periods, or
variable incubation periods
Usually, immunity generated by a killed vaccine is not as effective or long lasting as immunity stimulated
by a live attenuated vaccine
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The live vaccine more closely mimics the natural disease
Killed vaccines are easier to make though, and pose no risk for vaccine-associated risk
The live, attenuated, intranasal, cold-adapted influenza vaccine (or just live, attenuated influenza
vaccine for short) has a weakened form of live flu virus, and is given by a nasal spray instead of injection
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Cold adapted – means the virus can grow int eh nose and throat, but not in the lower
respiratory tract, where the temperature is higher
The live, attenuated flu vaccine is more effective for kids, than the inactivated flu vaccine
There is always a small risk that an attenuated vaccine strain will revert to a more virulent form in the
host
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Vaccine-acquired paralytic-poliomyelitis (VAPP) – happens in 1 outta every 3 million times the
polio vaccine is given
o Since polio was eradicated in the 70’s in the US, the only cases of paralysis from polio
since then have come from VAPP
o So they now recommend using only the inactivated polio vaccine in the US
o Countries that didn’t eradicate it though still use the live vaccine
o Immunization rates need to stay high, to prevent VAPP from spreading
The first licensed rotavirus live vaccine caused intussusception of the intestine, so they had to
get rid of that and make new ones with less risk
What type of response does the vaccine elicit:
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Live, attenuated vaccines – induces B cells, CD8+ T cells, and CD4+ T cells
Inactivated organisms, protein antigens, and capsular polysaccharide with a protein carrier –
induces B cells and CD4+ T cells, but no CD8+ T cells
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Capsular polysaccharides alone – induces only B cells
T-cell-independent antigens are characterized by low antibody titers and little memory response,
especially in children less than 18 months old
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Capsular polysaccharides induce B cell production of antibody, without any T cell help
If you covalently couple (conjugate) the polysaccharide to a protein antigen, the conjugated
vaccine instead causes a T-cell dependent response, due to the protein antigen
o T-cell dependent antigens cause high antibody levels in young infants, and primes for
strong booster responses at revaccination, due to good memory
The conjugation of pneumococcal capsular polysaccharides to protein antigens also generates
both B cell and T cell – dependent responses, and has caused herd immunity of invasive
pneumococcal disease
Secretory IgA antibodies produced at the mucosal surface, offer protection against some mucosal
pathogens, like flu, polio, rotavirus, etc.
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Live attenuated vaccines given to mucosal sites, can induce secretory immunity at the site of
initial pathogen contact
Correlates of protection – what type of immune response is needed to protect from the pathogen
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Some vaccines only induce serum antibodies – ex: HAV, polio, rabies, diphtheria, tetanus,
pertussis, and extracellular encapsulated bacteria
Other vaccines need both antibody levels and function to protect – ex: mumps, rubella, HIV,
meningococci, and pneumococci
Secretory antibodies protect against pathogens that need to replicate on the mucosal surface
o Ex: flu, polio, and rotavirus
Some vaccines need the T cell response – ex: measles, varicella
How old you are when you’re immunized is important in determining the immune response to the
vaccine
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Newborns receive IgG antibody from their moms, giving them transient protection against some
disease that their mom was immune to
o Breast milk also has secretory IgA antibodies that protect against intestinal and
respiratory tract infections, that the mom was immune to
o Both are passive immunization
o Mom antibodies may prevent responses to live vaccines though
o At birth, the humoral system isn’t fully developed and won’t have a good response to
polysaccharide antigens, but it will respond well to protein antigens
The elderly also have decreased immune responses, due to immune senescence
o So they’re more susceptible to infections
How to pick an antigen from a disease:
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Immune responses are most often against surface things that the pathogen uses when it invades
Sometimes all strains of a pathogen have that antigen, and sometimes some strains do and
some strains don’t, so you use multiple antigens for those vaccines
Antigenic drift (minor antigen changes) happen every year in flu virus (influenza), causing new
strains that need new vaccines
o Also, major antigen changes happen every decade, called antigenic shift
Some populations are at higher risk for diseases we can vaccinate:
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Influenza – people with heart or lung disease, or those older than 65, or younger than 6 months,
are at greater risk, and should be vaccinated
Sickle cell disease – causes asplenia, which makes them more at risk for infections with
encapsulated organisms, especially pneumococci
o They should get the pneumococcal conjugate vaccine
o People without spleens are also at the same risk, as well as for flu and meningococci
Old people – pneumococci and flu vaccines
Health care workers – HBV and rubella
Immunocompromised – shouldn’t get live attenuated vaccines, cause it may be pathogenic
enough to cause disease
The DTaP vaccine (diphtheria, tetanus, acellular pertussis) – the oldest and most successful combination
vaccine used in children
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It consists of a combo of 2 toxoids (diphtheria and tetanus) and inactivated parts of Bordetella
pertussis
All pertussis vaccines include pertussis toxin
DTaP is preferred to be given at 2, 4, and 6 months old, followed by booster doses at 15 and 18
months, and 4 to 6 years old
Then a booster of tetanus toxoid and diphtheria are given every 5-10 years
Recently, a new vaccine of tetanus toxoid, reduced dose diphtheria toxoid, and pertussic components,
was released, called Tdap
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Get Tdap at 11 to 12 years old, and a pertussis booster later in adolescence
Also, adults who had DTAP, should get Tdap