Types of Vaccines
Killed vs Modified Live
When designing a vaccine, efficacy and safety are the primary considerations.
These two principles appear to be mutually incompatible. In order to offer immunity against
disease the vaccine model should mimic the native antigen and yet should not cause
pathology, i.e., clinical signs of disease. Killed vaccines, also known as fully attenuated
vaccines, until recently have been the safest vaccine option available. They are safer
because unlike the modified live vaccines they do not shed virus into the environment nor
can they ever revert to virulence. However, in order to maximize their effectiveness, killed
vaccines are normally used with adjuvants that can cause their own problems. The immune
system is antigen-driven. This means that in order to mount an effective immune
response, the body must "see" the antigen for as long as possible. Once the antigen is
eliminated the response is terminated. Many different compounds have been used to
enhance the efficacy of killed vaccines, but the rational behind their use is to prolong the
antigenic stimulus of the primary immune response.
In comparison, th emodeified live vaccines are more like the original pathogen in the way
they elicit an immune reaction. In general, vaccines that contain the living organisms will
produce a stronger and a longer-lasting immunity, but their virulence must be reduced to a
safe level. This process is called attenuation. Reducing the virulence of bacteria is
accomplished by culturing them under unusual conditions. For example, one can make
them dependent on a growth meduim that is not available in the living animal so they cannot
reproduce. Once introduced into the body these bacteria can elicit the expected immune
response, but die off so rapidly that they do not cause the disease. When the pathogen is
a virus a different strategy is used - cell culture in cells or in a species for which the
organism is not normally adapted. After many passages through these foreign cell lines the
virus is unable to produce disease when reintroduced into its original host. Another issue
associated with the use of MLV (Modified Live Virus) is possible contamination with other
pathogens. One also should be aware this is not just one organism, but a population.
Therefore it is conceivable that deleterious mutations might occur. So you can see there
are problems associated with both types of vaccines and some choice between safety and
efficacy that need to be made.
Killed vs Modified Live
When designing a vaccine, efficacy and safety are the primary considerations.
These two principles appear to be mutually incompatible. In order to offer immunity against
disease the vaccine model should mimic the native antigen and yet should not cause
pathology, i.e., clinical signs of disease. Killed vaccines, also known as fully attenuated
vaccines, until recently have been the safest vaccine option available. They are safer
because unlike the modified live vaccines they do not shed virus into the environment nor
can they ever revert to virulence. However, in order to maximize their effectiveness, killed
vaccines are normally used with adjuvants that can cause their own problems. The immune
system is antigen-driven. This means that in order to mount an effective immune
response, the body must "see" the antigen for as long as possible. Once the antigen is
eliminated the response is terminated. Many different compounds have been used to
enhance the efficacy of killed vaccines, but the rational behind their use is to prolong the
antigenic stimulus of the primary immune response.
In comparison, th emodeified live vaccines are more like the original pathogen in the way
they elicit an immune reaction. In general, vaccines that contain the living organisms will
produce a stronger and a longer-lasting immunity, but their virulence must be reduced to a
safe level. This process is called attenuation. Reducing the virulence of bacteria is
accomplished by culturing them under unusual conditions. For example, one can make
them dependent on a growth meduim that is not available in the living animal so they cannot
reproduce. Once introduced into the body these bacteria can elicit the expected immune
response, but die off so rapidly that they do not cause the disease. When the pathogen is
a virus a different strategy is used - cell culture in cells or in a species for which the
organism is not normally adapted. After many passages through these foreign cell lines the
virus is unable to produce disease when reintroduced into its original host. Another issue
associated with the use of MLV (Modified Live Virus) is possible contamination with other
pathogens. One also should be aware this is not just one organism, but a population.
Therefore it is conceivable that deleterious mutations might occur. So you can see there
are problems associated with both types of vaccines and some choice between safety and
efficacy that need to be made.
Recominant
Grat strides have been made in recombinant technology and the future will bring even more
advances leading to baccines that may offer better protection and greater safety. A
recombinant is defined as a virus, a bacterium or other microorganism in which the genetic
material has been artifically modified. This alteration usually involves deletion of all or part
of a gene or the insertion of one or more genes from another organism. So far, the United
States Department of Agriculture has classified three different type of recominant vaccines.
The first class is called Subunit Vaccines.
It really is not necessary for the an animal's immune system to "see" the entire infectious
organism in order to mount an immune response. Often all that is required is for only small
portion or protein fragment to act as the antigen. An example of a subunit vaccine is one
developed by Rhone Meriux scientists (now known as Merial) against Lyme disease. This
vaccine is made of purified Outer surface protein A. After mapping the genome of the
bacteria Borrelia burgdorferi, it was determined that this protein evoked the greatest
antigenic response. Recombinant techniques allow for the isolation of this DNA fragment
and its amplified expression. It then is purified and used to manufacture the vaccine.
Besudes safety, one of the greatest advantages of this type of vaccine is that a simple blood
test can distinquish between animals that have been vaccinated and those that are infected
naturally.
The second category is recombinant Gene-Deleted Vaccines.
These can be considered a type of genetically attentuated modified live vaccine. Those
parts of the pathogen that can cause disease are either removed or rendered nonfunctional.
The third type is called Recombinant Vectored Vaccines.
Recombinant techniques are used to isolate and remove the immune-inducing genes from a
pathgenic virus. These genes then are inserted into a nonvirulent vector virus. This has
the potential to be a very effective type of vaccine because both a humoral and a
cell-mediated immune response are elicited. Class III vaccines may also allow for alternative
methods of vaccination, for instance, an oral mode of administration. They also have the
potential for immunization against more than one type of infection. The advances in sagety
and efficacy made possible by this new technology bode well for the future health of our pets.
Vaccine Failure
It may require one to two weeks or more to develop an effective immune response after a
course of vaccination. If the animal is exposed to an infectious agent prior to vaccination or
shortly after, the vaccine will not have had time to induce immunity and the puppy will
develop clinical signs of the disease. This also will occur if the puppy was incubating the
disease at the time it was vaccinated. In fact, the modified live vaccines can cause
something called immunosuppression, so vaccinating a puppy that already is sick only will
make matters worse. Canine parvovirus, canine distemper and the use of polyvalent
vaccines that contain these attenuated iruses hve been implicated in inducing immune
dysfunction. Other factors that can cause immunosuppression are stresses including
pregancy, malnutrition, concurrent infections, not allowing enough time between scheduled
vaccinations and the use of drugs such a prednisone. Another cause of vaccine failure is
incorrect admistration, including splitting a vial between puppies.
However, the most common reason for vaccination failure is thought to be the presence of
maternal antibody. This is a passive immunity gained from the dam's colostrum during the
first 72 hours of nursing. maternal antibody interferes more with viral vaccines than bacterial
vaccines and with the parvovirus vaccines more than any other type of viral vaccine.
Unfortunately, the amount of antigen that causes disease is less thank that needed to
overcome maternal antibodies, so there is a period of vulnerablity when the protection
afforded by maternal antibodies is not sufficient to prevent disease and the puppy's immune
system is not yet fully functioning. It is very important not only to isolate the puppy from
contact with other dogs, but to maintain a strict hygenic regime. A bleach solution diluted
1:10 with water will kill even the parvo virus, but remember to thoroughly rinse with clean
water before allowing the puppy to contact the bleached surface.
Grat strides have been made in recombinant technology and the future will bring even more
advances leading to baccines that may offer better protection and greater safety. A
recombinant is defined as a virus, a bacterium or other microorganism in which the genetic
material has been artifically modified. This alteration usually involves deletion of all or part
of a gene or the insertion of one or more genes from another organism. So far, the United
States Department of Agriculture has classified three different type of recominant vaccines.
The first class is called Subunit Vaccines.
It really is not necessary for the an animal's immune system to "see" the entire infectious
organism in order to mount an immune response. Often all that is required is for only small
portion or protein fragment to act as the antigen. An example of a subunit vaccine is one
developed by Rhone Meriux scientists (now known as Merial) against Lyme disease. This
vaccine is made of purified Outer surface protein A. After mapping the genome of the
bacteria Borrelia burgdorferi, it was determined that this protein evoked the greatest
antigenic response. Recombinant techniques allow for the isolation of this DNA fragment
and its amplified expression. It then is purified and used to manufacture the vaccine.
Besudes safety, one of the greatest advantages of this type of vaccine is that a simple blood
test can distinquish between animals that have been vaccinated and those that are infected
naturally.
The second category is recombinant Gene-Deleted Vaccines.
These can be considered a type of genetically attentuated modified live vaccine. Those
parts of the pathogen that can cause disease are either removed or rendered nonfunctional.
The third type is called Recombinant Vectored Vaccines.
Recombinant techniques are used to isolate and remove the immune-inducing genes from a
pathgenic virus. These genes then are inserted into a nonvirulent vector virus. This has
the potential to be a very effective type of vaccine because both a humoral and a
cell-mediated immune response are elicited. Class III vaccines may also allow for alternative
methods of vaccination, for instance, an oral mode of administration. They also have the
potential for immunization against more than one type of infection. The advances in sagety
and efficacy made possible by this new technology bode well for the future health of our pets.
Vaccine Failure
It may require one to two weeks or more to develop an effective immune response after a
course of vaccination. If the animal is exposed to an infectious agent prior to vaccination or
shortly after, the vaccine will not have had time to induce immunity and the puppy will
develop clinical signs of the disease. This also will occur if the puppy was incubating the
disease at the time it was vaccinated. In fact, the modified live vaccines can cause
something called immunosuppression, so vaccinating a puppy that already is sick only will
make matters worse. Canine parvovirus, canine distemper and the use of polyvalent
vaccines that contain these attenuated iruses hve been implicated in inducing immune
dysfunction. Other factors that can cause immunosuppression are stresses including
pregancy, malnutrition, concurrent infections, not allowing enough time between scheduled
vaccinations and the use of drugs such a prednisone. Another cause of vaccine failure is
incorrect admistration, including splitting a vial between puppies.
However, the most common reason for vaccination failure is thought to be the presence of
maternal antibody. This is a passive immunity gained from the dam's colostrum during the
first 72 hours of nursing. maternal antibody interferes more with viral vaccines than bacterial
vaccines and with the parvovirus vaccines more than any other type of viral vaccine.
Unfortunately, the amount of antigen that causes disease is less thank that needed to
overcome maternal antibodies, so there is a period of vulnerablity when the protection
afforded by maternal antibodies is not sufficient to prevent disease and the puppy's immune
system is not yet fully functioning. It is very important not only to isolate the puppy from
contact with other dogs, but to maintain a strict hygenic regime. A bleach solution diluted
1:10 with water will kill even the parvo virus, but remember to thoroughly rinse with clean
water before allowing the puppy to contact the bleached surface.
