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effective, not everyone can receive these vaccines. Children
with weakened immune systems-for example, those who are
undergoing chemotherapy-cannot get live vaccines.
* Inactivated vaccines also fight viruses and bacteria. These
vaccines are made by inactivating, or killing, the germ during
the process of making the vaccine. The inactivated polio vaccine
is an example of this type of vaccine. Inactivated vaccines
produce immune responses in different ways than live attenuated
vaccines; often, multiple doses are necessary to build up and/or
maintain immunity.
* Toxoid vaccines prevent diseases caused by bacteria that
produce toxins (poisons) in the body. In the process of making
these vaccines, the toxins are weakened so they cannot cause
illness. Weakened toxins are called toxoids. When the immune
system receives a vaccine containing a toxoid, it learns how to
fight off the natural toxin. The DTaP vaccine contains diphtheria
and tetanus toxoids.
* Subunit vaccines include only parts of the virus or bacteria,
or subunits, instead of the entire germ. Because these vaccines
contain only the essential antigens and not all the other molecules
that make up the germ, side effects are less common. The
pertussis (whooping cough) component of the DTaP vaccine is
an example of a subunit vaccine.
* Conjugate vaccines fight a different type of bacteria. These
bacteria have antigens with an outer coating of sugar-like
substances called polysaccharides. This type of coating disguises
the antigen, making it hard for a young child's immature
immune system to recognize it and respond to it. Conjugate
vaccines are effective for these types of bacteria because they
connect (or conjugate) the polysaccharides to antigens that the
immune system responds to very well. This linkage helps the
immature immune system react to the coating and develop an
immune response. An example of this type of vaccine is the
Haemophilus influenzae type B (Hib) vaccine.

Vaccines Require More
Than One Dose
There are four reasons that babies-and even teens
or adults-who receive a vaccine for the first time
may need more than one dose:
* For some vaccines (primarily inactivated vaccines),
the first dose does not provide as much immunity
as possible. So, more than one dose is needed to
build more complete immunity. The vaccine that
protects against the bacteria Hib, which causes
meningitis, is a good example.
* For some vaccines, after a while, immunity
begins to wear off. At that point, a " booster "
dose is needed to bring
immunity levels back up.

This booster dose usually occurs several years after the initial
series of vaccine doses is given. For example, in the case of the
DTaP vaccine, which protects against diphtheria, tetanus and
pertussis, the initial series of four shots that children receive as
part of their infant immunizations helps build immunity. But a
booster dose is needed at 4 years through 6 years old. Another
booster against these diseases is needed at 11 years or 12 years
of age. This booster for older children-and teens and adults,
too-is called Tdap.
* For some vaccines (primarily live vaccines), studies have shown
that more than one dose is needed for everyone to develop the
best immune response. For example, after one dose of the MMR
vaccine, some people may not develop enough antibodies to
fight off infection. The second dose helps make sure that almost
everyone is protected.
* Finally, in the case of flu vaccines, adults and children (6
months and older) need to get a dose every year. Children 6
months through 8 years old who have never gotten a flu vaccine
in the past or have only gotten one dose in past years need two
doses the first year they are vaccinated. Then, an annual flu
vaccine is needed because the flu viruses causing disease may be
different from season to season. Every year, flu vaccines are made
to protect against the viruses that research suggests will be most
common. Also, the immunity a child gets from a flu vaccination
wears off over time. Getting a flu vaccine every year helps keep
a child protected, even if the vaccine viruses don't change from
one season to the next.

The Bottom Line
Some people believe that naturally acquired immunity-
immunity from having the disease itself-is better than the
immunity provided by vaccines. However, natural infections
can cause severe complications and be deadly. This is true even
for diseases that many people consider mild, like chickenpox.
It is impossible to predict who will get serious
infections that may lead to hospitalization.
Vaccines, like any medication, can cause side
effects. The most common side effects are
mild. However, many vaccine-preventable
disease symptoms can be serious, or even
deadly. Although many of these diseases are
rare in this country, they do circulate around
the world and can be brought into the U.S.,
putting unvaccinated children at risk. Even with
advances in health care, the diseases that vaccines
prevent can still be very serious - and vaccination
is the best way to prevent them. Adapted from
the National Institute of Allergy and Infectious
Diseases, Understanding Vaccines https://www.
niaid.nih.gov/research/howvaccines-work.
For more information on vaccines call 800-CDCINFO (800-232-4636) or visit www.cdc.g.

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York County Medicine Winter 2020

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