clude: (1) lack of access to health care, (2) lack of
knowledge about appropriate immunizations for chil-
dren, (3) misconceptions about contraindications to
vaccination (reasons that vaccination may be inadvis-
able), and (4) missed opportunities for immuniza-
tions.
Controversy over Vaccination
Public fears about the possibility of adverse cen-
tral nervous system effects of immunizations have fol-
lowed several routine childhood vaccines. In the
1970s there were concerns over neurologic side ef-
fects (primarily, encephalopathy) of pertussis vaccina-
tion. In the mid-1990s there were concerns over
central nervous system demyelinating disease (e.g.,
Guillain-Barré syndrome, multiple sclerosis) and the
hepatitis B vaccine. While concerns over pertussis and
hepatitis B vaccines have largely diminished in the
United States, fear increased in the late 1990s over a
possible association between autism and the MMR
vaccine.
Controversy over the MMR vaccine followed pub-
lication of an article in the journal Lancet in early
1998 written by Andrew Wakefield. Based on observa-
tions and investigations made in twelve children, the
authors suggested a link among the MMR vaccine,
chronic intestinal inflammation, and autism.
Two subsequent epidemiologic studies, by B.
Taylor and L. Dales, failed to identify an association
between the MMR vaccine and autism. The Taylor
study, from the United Kingdom, demonstrated in-
creasing rates of autism, but a comparison of rates be-
fore and after the MMR vaccine was introduced in the
United Kingdom in 1988 failed to uncover a link be-
tween the two. The Dales study, from California,
demonstrated an almost fourfold relative increase
(373%) in autism between 1980 and 1994. Immuniza-
tion rates, however, increased by only 14 percent dur-
ing the same period.
Until the cause or causes of autism are better de-
fined, controversy will continue in this area. Current-
ly, there is little, if any, scientific evidence linking the
MMR vaccine and autism. Meanwhile, the global
eradication of measles is still a possibility through
widespread use of measles-containing vaccines. Erad-
ication of measles would eliminate the estimated
880,000 deaths that occur worldwide as a result of
measles infection.
The Future
The immunization schedule is constantly evolv-
ing. Future changes include vaccines against addi-
tional diseases, new vaccine combinations, and novel
approaches to immunization. New routes for vaccine
administration (e.g., nasal vaccines, vaccines incorpo-
rated into foods) are also being evaluated.See also: BIRTH DEFECTS; RUBELLABibliography
American Academy of Pediatrics. Committee on Infectious Diseas-
es. Red Book, 2000: Report of the Committee on Infectious Diseases,
25th edition. Elk Grove Village, IL: American Academy of Pe-
diatrics, 2000.
American Academy of Pediatrics. Committee on Infectious Diseas-
es. ‘‘Recommended Childhood Immunization Schedule:
United States, January–December 2001.’’ Pediatrics 107, no. 1
(2001):202–204.
Centers for Disease Control and Prevention. ‘‘Achievements in
Public Health, 1900–1999: Impact of Vaccines Universally
Recommended for Children—United States, 1990–1998.’’
Morbidity and Mortality Weekly Report 48, no. 12 (1999):243–
248.
Centers for Disease Control and Prevention [web site]. Atlanta, GA,- Available from http://www.cdc.gov; INTERNET.
Dales, L., S. J. Hammer, and N. J. Smith. ‘‘Time Trends in Autism
and in MMR Immunization Coverage in California.’’ Journal
of the American Medical Association 285, no. 9 (2000):1183–
Radetsky, Michael. ‘‘Smallpox: A History of Its Rise and Fall.’’ Pedi-
atric Infectious Disease Journal 18, no. 2 (1999):85–93.
Taylor, Brent, Elizabeth Miller, C. Paddy Farrington, Maria-
Christina Petropoulos, Isabelle Favot-Mayaud, Jun Li, and
Pauline A. Waight. ‘‘Autism and Measles, Mumps, and Rubel-
la Vaccine: No Epidemiologic Evidence for a Causal Associa-
tion.’’ Lancet 353 (June 12, 1999):2026–2029.
Wakefield, A.J., S. H. Murch, A. Anthony, J. Linnell, D. M. Casson,
M. Malik, M. Berelowitz, A. P. Dhillon, M. A. Thomson, P.
Harvey, A. Valentine, S. E. Davies, and J. A. Walker-Smith.
‘‘Ileal-Lymphoid-Nodular Hyperplasia, Non-specific Colitis,
and Pervasive Developmental Disorder in Children.’’ Lancet
351 (February 28, 1998):637–641.
Alan Uba
IN VITRO FERTILIZATION
In vitro fertilization is the term for a process whereby
a mature egg from the female and a sperm from the
male are placed in culture media where fertilization
can occur. For humans, the first clinically successful
in vitro fertilization occurred in 1978. If accom-
plished, cell division results in six to eight cells in
about forty-eight hours, or a blastocyst of 100 cells in
about 120 hours. One or more can then be trans-
ferred into the uterus with a 20 percent to 60 percent
expectation of pregnancy depending on many vari-
ables, including age, cause of infertility, and number
of fertilized eggs, or pre-embryos, transferred.
Pregnancy rates increase with number of pre-
embryos transferred, as do the multiple pregnancy
rates. In the United States (1998), 360 clinics con-
ducted 80,634 treatment cycles; 31 percent of deliver-204 IN VITRO FERTILIZATION