V

vaccine A substance that initiates an IMMUNE
RESPONSEto produce antibodies that prevent INFEC-
TIONby the particular PATHOGEN. Vaccines contain
attenuated live (weakened) or killed pathogens
such as viruses or BACTERIA. The antigens of these
pathogens activate the body’s immune response,
stimulating B-cell lymphocytes to produce anti-
bodies specific to them. Genetic engineering
makes it possible to produce large quantities of
many vaccines in relatively short order. There are
four types of vaccines:

• Attenuated vaccines contain live but weakened
  viruses to produce the strongest immune
  response. Laboratory manipulation of the VIRUS
  can establish narrow parameters of survival for
  the virus the vaccine carrier, such as tempera-
  ture or acidity. These manipulations reduce the
  risk that the vaccine could cause infection,
  though such a risk exists. Often an attenuated
  vaccine requires only a single DOSEto establish
  full and long-term IMMUNITY.


• Inactivated vaccines contain killed bacteria or
  viruses. These pathogens still carry the antigens
  that will stimulate the immune response to
  produce antibodies but are incapable of causing
  infection. Though safer than attenuated vac-
  cines, inactivated vaccines often require multi-
  ple doses or provide limited immunity.


• Acellular vaccines, also called subunit vaccines,
  contain particles of the virus or bacteria. These
  particles carry enough ANTIGENto stimulate an
  immune response but are not complete enough
  to cause infection.


• Toxoid vaccines generate antibodies for the tox-
  ins certain bacteria generate when they cause
  infection. Tetanus and DIPHTHERIAare illnesses

due to such toxins and the vaccines for them

provide antibodies for the toxins rather than

the bacteria that cause the illness.

Vaccines prevent many infectious diseases that

were once major killers. Vaccination has essen-

tially eliminated SMALLPOXworldwide, for exam-

ple, and is close to eliminating POLIOMYELITIS. Some

vaccines, such as for tetanus and pertussis, require

multiple doses or periodic booster doses to estab-

lish full immunity. Because vaccines are effective

for only the specific pathogens they contain, rap-

idly mutating pathogens such as the INFLUENZA

virus require a new vaccine for each strain.

VACCINES

ANTHRAX CHICKENPOX/shingles

CHOLERA (varicella zoster viruses)

DIPHTHERIA diptheria, tetanus,

Haemophilus influenzae acellular PERTUSSIS(DtaP)

type b (Hib) HEPATITISA (HAV)

hepatitis B (HBV) INFLUENZA

LYME DISEASE MEASLES

meningococcal vaccine measles, MUMPS, RUBELLA

monkeypox (MMR)

mumps pertussis

plague pneumococcal vaccine

POLIOMYELITIS RABIES

rotavirus rubella

rubeola tetanus

TUBERCULOSIS typhoid

yellow FEVER

Vaccines may not be effective in establishing

immunity in people who are IMMUNOCOMPROMISED.

Some people have allergies to the ingredients of

the vaccine. Vaccines that contain attenuated live

viruses sometimes use the preservative thimerosal,

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