vaccine was licensed in the United States in 1963, some
400,000 cases of measles were reported on average each year.
Yet because virtually all children contracted measles, the
actual number of cases probably approached that of the
entire birth cohort (3.5 million to 4 million cases per
By the early 1980s, however, the annual incidence of reported measles
cases had been reduced by more than 99 percent, to less than
Unfortunately, later in that decade, the vaccination rate decreased and
an outbreak of measles occurred between 1989-1991, when more
than 55,000 cases and greater than 120 measles-related
deaths were reported in the United States.
This increase was attributable to two major types of out-breaks: those
among unvaccinated preschool-age children and those among
vaccinated school-age children; this latter group was
susceptible because approximately 5 percent of those
receiving a single dose of measles-containing vaccine do not
mount a protective immune response.
As a result of this resurgence, a two-dose strategy for measles
vaccination was recommended in 1989. The first dose of
vaccine was to be given as measles, mumps and rubella
vaccine (MMR) at age 15 months, and the second dose also as
MMR at entrance to middle school or junior high school. As
of 1997, the Academy, the American Academy of Family
Physicians and the Centers for Disease Control and
Prevention (CDC) recommended that the second dose be
administered at school entry. By 2001, the national goal is
that all school-age children will have received two doses of
Q. How effective is the current
strategy of measles vaccination?
A. The current
two-dose strategy has been very effective. Both
epidemiologic and laboratory evidence suggest the
transmission of indigenous measles was interrupted the
United States for the first time during 1993. During1997,
the latest year for which data are available, there was a
provisional total of only 135 confirmed measles cases. This
is the lowest number of cases ever.
Even though indigenous measles transmission has been virtually
eliminated, measles cases caused by importation of the virus
from other countries continue to occur. A total of 57 of the
135 (42 per cent) measles cases reported in 1997 were
documented as international importations, primarily from
Europe and Asia.
Q. Why should we still vaccinate
against measles when cases are so uncommon?
A. Although the
number of measles cases in the United States is at an
all-time low, there continues to be substantial measles
activity throughout the Americas and the remainder of the
Between January 1997 and February 1998, some 88,485 suspected measles
cases were reported from the Americas, with Brazil and
Canada having the greatest number of cases. The highest
rates of measles infections outside the Americas are
observed in Africa, Western Europe and Southeast Asia.
Because, of the continued activity of measles throughout the world,
including countries in our own back yard (Canada), U.S.
children may contract infection from travelers from these
endemic countries. This is true, even considering the
presently high vaccination rate in the United States; large
measles outbreaks have been observed repeatedly, even in
countries that have achieved high levels of measles
vaccination coverage and have recorded several years of low
incidence of disease.
A reduction in measles immunization rates would substantially increase
the potential size of any outbreak, contributing to
increased disease-associated morbidity and mortality rates.
Although measles usually is a self-limited infection among normal
children in developed countries, complications including
otitis media, bronchopneumonia, laryngotracheobronchitis
(croup) and diarrhea are not uncommon, especially in young
children. Less common, but more serious complications,
include acute encephalitis and sub-acute sclerosing
Death from measles infection, usually attributed to respiratory and
neurologic complications, occurred in one to two of every
1,000 cases reported in the United States in the pre-vaccine
era. In developing countries, measles remains one of the
leading causes of child mortality, responsible for
approximately 10 percent of all deaths among children
younger than 5 years.
Case fatality rates are higher among immunocompromised children,
including those with underlying malignancy and HIV
infection. Measles vaccination of asymptomatic children with
HIV infection is safe, whereas natural infection when they
have AIDS may be devastating.
Q. What are the known complications of
A. Measles vaccine is very safe; most
persons have no reactions.
About 5 percent to 15 percent of vaccinees may develop a fever five to 12
days after MMR vaccination. The fever usually lasts one to
two days and usually is not associated with other symptoms.
About 5 percent of MMR recipients may develop a transient rash one to two
weeks after immunization.
Central nervous system disturbances, such as encephalitis, have been
reported with a frequency of less than one per 1 million
doses administered, a frequency many times lower than the
incidence of serious central nervous system disorders that
follow natural infection. Because the incidence of
encephalitis or encephalopathy after measles vaccination is
lower than the observed incidence of encephalitis of unknown
etiology, most of the reported cases maybe temporally,
rather than causally, associated.
Measles vaccine also is safe when administered to children infected with
HIV if they are asymptomatic or not severely
immunocompromised. Measles vaccine is recommended for
these children because of this safety profile and because of
reports of severe and often fatal measles infection in
children with AIDS.
Q. Is there a link between measles
vaccination and autism?
is a chronic developmental disorder sometimes noted in
infancy as impaired attachment, but more often first
identified in toddlers from age 18 months to 30 months.
Because MMR vaccine is administered just before the peak age
of onset of autism, a temporal relationship between
vaccination and onset of autism is expected to be common.
Although the cause of autism is unknown in most instances, the theory
favored by many experts is that it is a genetically based
disorder that occurs before birth. Evidence that genetics is
an important, but not exclusive, cause of autism includes a
3 percent to 8 percent risk of recurrence in families with
one affected child.
To date, there is no convincing evidence that any vaccine causes autism.
Stimulated by a hypothesis articulated by a British investigative team, a
link between MMR vaccine and autism has been suggested by
some parents of children with autism. Based on data from 12
patients, the British physicians speculated that MMR vaccine
may have been the possible cause of bowel problems, leading
to a decreased absorption of essential vitamins and
nutrients and resulting in developmental disorders like
The theory that autism may be caused by poor absorption of nutrients due
to bowel inflammation was not supported by the clinical
data. Specifically, the behavioral problems appeared before
the onset of symptoms of inflammatory bowel disease in at
least four of the 12 reported cases. That is, the effect
preceded the cause. The authors even acknowledged in their
original work that the association was speculative and that
they "did not prove an association."
Furthermore, the same authors have published another study in which
highly specific laboratory assays in patients with
inflammatory bowel disease, the purported mechanism for
autism after MMR vaccination., were negative for measles
Other recent investigations do not support a causal association between
MMR and autism or inflammatory bowel disease.
A Working Party on MMR Vaccine of the United Kingdoms Committee on
Safety of Medicines recently evaluated several hundred
reports of autism, inflammatory bowel disease or similar
disorders developing after receipt of MMR or MR vaccines.
The Working Party conducted a systematic, standardized
review of parental and physician information and concluded
that the information available "did not support the
suggested causal associations or give cause for concern
about the safety of MMR or MR vaccines."
Finally, a recently published population-based study from Britain
identified all 498 known cases of autism among those born in
1979 or later in certain districts of London and linked the
cases to an independent regional vaccination registry. The
authors showed that the known number of cases of autism had
been increasing since 1979, with no jump after the
introduction of MMR vaccine in Britain in 1988.
They also showed that, at age 2 years, the MMR vaccination coverage among
the children with autism was almost identical to that in
children in the same birth cohorts in the whole region,
providing evidence of an overall lack of association with
Finally, the authors showed that the first diagnosis of autism or initial
signs of behavioral regression were no more likely to occur
within time periods following vaccination than during other
A study of the population of children in two communities in Sweden also
found no evidence of an association between MMR vaccination
and autism. That study found no difference in the prevalence
of autism in children born after the introduction of MMR
vaccination in Sweden compared with children born before.
Only 15 cases of autism behavior disorder after immunization were
reported to the Vaccine Adverse Events Reporting System
(VAERS) between January 1990 and February 1998. Because of
the small number of reports over an eight-year period, the
cases reported are likely to represent unrelated chance
occurrences that happened around the time of vaccination.
Vaccines administered proximal to the onset of autism included
diphtheria, tetanus, pertussis (DPT), oral polio vaccine,
Haemophilus influenzae type b, hepatitis B and MMR. If
measles vaccine, or any other vaccine causes autism, then it
would have to be a very rare occurrence since millions of
children have received vaccines without ill health effects.
Q. How are uncommon adverse events
possibly associated with vaccination detected?
A. To assure the safety of vaccines,
the CDC, the Food and Drug Administration (FDA), the
National Institutes of Health (NIH) and other federal
agencies routinely monitor and conduct research to examine
any new evidence suggesting possible problems with the
safety of vaccines.
Currently, the CDC is conducting a study in metropolitan Atlanta to
further evaluate any possible association between MMR
vaccination and autism. Results are expected sometime in
Health care providers who administer vaccines are required to report to
VAERS certain adverse. health events that occur in persons
who have received vaccines. Some of these reports are
related to vaccines, and other reports are not related but
occur from other causes and happen around the time vaccines
are given. The CDC and the FDA collect and analyze these
To report a health problem that follows vaccination, call VAERS at 800-
822-7967. The National Immunization Program has established
a National Immunization Information Hotline to help answer
vaccine questions: 800- 232-2522 (English) and 800-232-0233