 |
Infants
Vaccines
Different Types
|
Two
Main Types of Vaccines
Live,
attenuated vaccines
Live vaccines are
made from live viruses that have been grown under special laboratory
conditions so they are weakened, or attenuated, and thereby do not
cause the symptoms or complications of the disease. But they do
produce immunity, because the live vaccine virus displays the same
special markers on its outer surface as the wild-type virus. When the
live vaccine virus enters the body and begins replicating itself, the
immune system jumps into action. Each component of the immune system
does its part to process and destroy the antigen, and memory cells
develop to guard against the next invasion of the disease.
The entire immune system
responds to live vaccines as it does to infection from the wild-type
disease. Thus, live injected vaccines usually require only one dose
for lifelong immunity, just as one bout of measles or chickenpox will
make most people immune for life.
Live vaccines, however,
have several disadvantages. First, they usually require special
storage and handling to keep them alive. Second, they could overwhelm
a person who does not have a well-functioning immune system. This is
why live vaccines should generally be withheld if a person has a
weakened immune system.
Because of concern about
the possibility that a live vaccine virus could harm a fetus, these
vaccines are not given to pregnant women. Also, because antibodies
passed from the mother to the fetus may interfere with live injected
vaccines, these live vaccines are usually recommended at 12 months of
age or later.
Because live vaccines are
weak versions of the disease germs, they may cause a mild case of the
disease they were designed to prevent. For example, chickenpox
vaccination may cause a person to break out in a few pox or develop a
low-grade fever. In real chickenpox a person usually develops 200 pox
and substantial fever.
Live vaccines are used
for the following diseases:
| Measles |
Mumps |
Rubella |
Chickenpox |
| Polio (Oral) |
Typhoid (Oral) |
Tuberculosis |
|
| Yellow Fever |
Smallpox |
|
|
Inactivated
vaccines
Inactivated
vaccines consist of whole microbes that
have been killed by heat or chemicals (as in the inactivated polio
vaccine, IPV) or are simply the important part of the microbe that
provokes the immune system to respond (as in the hepatitis B
vaccine). Unlike live vaccines, inactivated vaccines cannot replicate
and so cannot cause even mild cases of the disease, but their
presence still prompts the immune system to respond.
The inactivated vaccines
cause a relatively weak response by the immune system, so usually the
vaccination must be repeated. The advantages to inactivated vaccines
include that they are not as fragile as live vaccines. Unlike live
vaccines, inactivated vaccines are safe for persons who have weakened
immune systems, for pregnant women, and for children under a year
old. The side effects are generally just soreness where the vaccine
was injected and possibly some fever shortly after vaccination.
Usually the outer coat of
bacteria is made of protein, and the inactivated vaccines mimic this
protein. Protein-based inactivated vaccines are used for the
following diseases:
| Influenza |
Polio (injected) |
Pertussis |
Plague |
| Hepatitis B |
Hepatitis A |
Lyme disease |
|
| Rabies |
Typhoid |
Cholera |
|
Some bacteria are literally sugarcoated. That is,
their outer surface is composed of complex sugars, or polysaccharides
. Vaccines against these bacteria must duplicate these special
coats. Unfortunately, pure polysaccharide vaccines don't work well in
infants and don't produce increasingly high antibody levels with
subsequent doses. The meningococcal vaccine and the pneumococcal
vaccine for older children and adults are pure polysaccharide
vaccines.
A superior vaccine is produced by joining
(conjugating) the polysaccharide to a protein. Conjugate vaccines are
effective in infants and boost antibody levels with subsequent doses.
The current Hib and the pneumococcal vaccine for infants and young
children are conjugate polysaccharide vaccines.
Toxoids are another kind of inactivated
vaccine. Instead of being made from killed germs, toxoids are made by
inactivating the poisons, or toxins, produced by the germs. After you
take the toxoid, your body is no better at fighting off infection to
those germs, but it is much, much better at fighting off the effects
of the germ's poison. The vaccines against tetanus and diphtheria are
toxoids.
This
information is excerpted from the book Vaccinating Your Child:
Questions and Answers for the Concerned Parent (Peachtree
Publishers, Ltd., 2000). The book's authors are Dr. Sharon G.
Humiston, a pediatrician and clinical researcher at the CDC and the
University of Rochester, and Cynthia Good, an award-winning
journalist and host of the television show "Good for
Parents".
|
