Measles Vaccines Reactions (Encephalopathy & Encephalitis)

Although the measles vaccine is administered by injection rather than by
the natural, respiratory route of infection, the host response is similar
to that evoked by the wild-type virus in all but two respects. The
immunized subject develops humoral and cellular immune responses some 48
hours earlier than the naturally infected host, and the recipient of the
vaccine does not develop clinical measles. Three classes of immune globulin
(IgA, IgG, and IgM) are produced and are detectable in the serum and nasal
mucus of vaccinated subjects (Bellanti et al., 1969).

The standard test of immunity to measles is based on the detection of serum
antibodies by the enzyme-linked immunosorbent assay method. Although the
titers of these antibodies induced by the vaccine tend to be somewhat lower
than those resulting from natural infection (Schwarz and Anderson, 1965),
immunity acquired by vaccination is long-lasting (Krugman, 1983).
Clinical Description
Encephalopathy refers to any acute or chronic acquired abnormality of,
injury to, or impairment of the function of the brain. Symptoms can include
alterations in state of consciousness or behavior, convulsions, headache,
and focal neurologic deficits. Encephalitis refers to an encephalopathy
caused by an inflammatory response in the brain. This is usually manifested
with systemic constitutional symptoms, particularly pleocytosis of the
cerebrospinal fluid (CSF). However, the terms encephalopathy and
encephalitis have been used imprecisely and even interchangeably in the
literature. The discussion that follows uses the terminologies of the
authors of the reports. However, if the authors used the term encephalitis,
but there was no documentation of pleocytosis in the CSF, "encephalitis" is
used in quotation marks. The annual incidence of encephalitis for the years
1950 to 1981 in Olmsted County, Minnesota, was 7.4 per 100,000 people
(Beghi et al., 1984; Nicolosi et al., 1986). The incidence in children less
than age 1 year was 22.5, in children between ages 1 and 4 years it was
15.2, and in children between ages 5 and 9 years it was 30.2 per 100,000.
Other estimates of encephalopathy for children less than age 2 years were
somewhat lower than those reported by Beghi et al. and Nicolosi et al.
cited above. Other estimates for annual incidence range from 5 per 100,000
people (Walker et al., 1988) to 10 per 100,000 people (Gale et al., 1990).
Chapter 3 contains a discussion of encephalopathy.

History of Suspected Association
The occurrence of encephalitis following a natural measles virus infection
is well described. The condition is quite severe, often leading to
permanent brain damage or even death. There may be no detectable pathologic
lesion, but in most cases some edema and demyelination are noted. Early
studies of the adverse events associated with measles vaccine concentrated
on "encephalitis." These are described below (Landrigan and Witte, 1973;
Nader and Warren, 1968).

The first report of encephalopathy following vaccination with the live
attenuated Edmonston B (Rubeovax) measles vaccine appeared in 1967 (Trump
and White, 1967). A 2-year-old girl developed unsteadiness 7 days following
vaccination. This was followed by pronounced generalized ataxia (diagnosed
as cerebellar ataxia), fever, vomiting, and an exanthem. There was
pleocytosis in the CSF 1 month after vaccination. The ataxia persisted for
at least 8 months. Because of the child's history and physical and
laboratory findings, the investigators attributed the condition to measles
vaccination. Two early case series investigations of neuralgic disorders
following measles vaccination included reports of "encephalitis." These are
discussed below.

Mumps affects the central nervous system as well, but it is more likely to
cause meningitis than encephalitis (Azimi et al., 1969). This condition
tends to be self-limited and has a good prognosis. Cases of pure
encephalitis following mumps are rare, but they can be quite severe.

Evidence for Association
Biologic Plausibility
Chapter 3 contains a discussion of the biologic plausibility for certain
types of encephalopathies and vaccination. As described above, natural
(wild-type) measles virus infection is associated with a well-described,
frequently very severe encephalitis.

Case Reports, Case Series, and Uncontrolled Observational Studies
Many uncontrolled observational studies in the literature describe the
occurrence of encephalopathy after administration of measles vaccine. These
are reviewed first. Data from similar studies regarding multivalent
preparations are described next. Individual case reports and unpublished
case reports from U.S. Public Health Service passive surveillance systems
are discussed last. There are no data regarding monovalent mumps vaccine
and encephalopathy.

Measles Vaccine The first published case of encephalopathy (acute
cerebellar ataxia) attributed to measles vaccine was discussed above (Trump
and White, 1967). Retrospective analyses of populations who have received
measles vaccine have been reported from many countries, including the
United States. These uncontrolled observational studies provide no
information on the concurrent background rates of encephalopathy. Table 6-2
summarizes case series and uncontrolled observational studies in which the
incidence rates of encephalopathy or encephalitis following administration
of measles vaccine were calculated by the authors.

Two case series addressed early concerns in the United States that measles
vaccine might cause encephalitis. The first was a report of 23 cases of
neurologic disease following measles vaccination in the United States from
January 1965 to February 1967 (Nader and Warren, 1968). The authors
characterized 18 of the 23 cases as "encephalitis" (described as including
disturbances of sensorium, seizure, major loss of motor function, and
cerebral edema; no data are provided regarding pleocytosis in the CSF). The
interval from vaccination to the onset of symptoms ranged between 3 and 24
days. Postmortem findings in one case revealed herpes simplex virus in
brain tissue. There were two cases of aseptic meningitis, two cases of
cerebellar ataxia, and one case of extraocular muscle paralysis. The
authors estimated a rate of 1.5 reported cases of "encephalitis" within a
4-week period of vaccination per 1 million doses of vaccine distributed.
They compared this with a background rate of 2.8 cases of encephalitis
(unrelated to vaccination or known parainfectious causes) per 1 million
children for any 4-week period. The authors concluded, ''No single clinical
or epidemiologic characteristic appears consistently in the reports of
cases of possible neurologic sequelae of measles vaccination" (p. 998).

A review of 84 patients with neurologic disorders occurring within 30 days
of vaccination against measles virus reported to the Centers for Disease
Control from 1963 to 1971 revealed 59 patients with extensive neurologic
disorders, which included encephalomyelitis (Landrigan and Witte, 1973).
The cases reported by Nader and Warren (1968) and discussed above are a
subset of the data of Landrigan and Witte (1973). Although in all 59
patients the onset of symptoms occurred between 1 and 25 days after
vaccination, in 45 it coincided with the period of maximal viral
replication (6 to 15 days after vaccination). Of 50 patients for whom
follow-up information was available (follow-up presumably from 1963 to
sometime before 1973), 26 recovered fully, 5 died (2 of the 5 had
pathologic features of Reye syndrome), and 19 were left with permanent
neurologic damage. Thirteen of the 59 patients were classified as having
encephalomyelitis. Long-term follow-up of 12 of the patients showed
residual neurologic signs in 3 patients. Long-term follow-up was available
for 31 of 36 patients considered to have encephalopathy. Ten of those 31
patients recovered fully, 5 died, and 16 were left with neurologic residua.
The authors calculated rates of "encephalitis" of 1.16 cases per 1 million
doses of vaccine distributed.
TABLE 6-2 Rates of Encephalitis/Encephalopathy After Measles Vaccination
from Uncontrolled Studies
See above URL for the table
* The authors thought that 5 of the 16 cases were possibly causally related
to the vaccine.
Among the recipients of more than 3 million doses of measles vaccine
(various strains, but mostly the Schwarz strain) in the United Kingdom
between 1968 and 1974, there were 47 cases of "encephalitis" (Beale, 1974).
The report does not discuss the criteria used for the diagnosis. Data on
the occurrence of encephalitis in temporal relation to administration of
measles vaccine for the years 1965-1976 in Canada showed a rate of 1.79
cases of encephalitis per 1 million doses of vaccine distributed (White,
1983). These data are based on hospital admissions associated with
International Classification of Diseases codes for "viral encephalitis
unspecified" and "acute viral encephalitis.''

In a report from the former East Germany (Dietzsch and Kiehl, 1976), there
were 7 central nervous system (CNS) complications out of 174,725
immunizations with an unstated vaccine, but it was probably one of the
strains from the former Soviet Union. Two febrile seizures, four cases of
encephalopathy, and one case of encephalitis (there was pleocytosis in the
CSF) were reported. Few clinical details were reported. Two of the patients
with encephalopathy and the patient with encephalitis recovered completely,
one patient with encephalopathy was left with a residual paralysis, and
another died of leukemia.

A report from the former Soviet Union (Ozeretskovskii and Gurvich, 1991)
referred to cases of encephalitis and encephalitic reaction caused by a
measles vaccine (probably the Smorodintsev strain), but offered no primary
data. The authors quote three rates per 100,000 vaccinees: 0.1, 0.02, and
190 cases. The rate of 0.02 is far below the acknowledged background rate
of encephalitis and the rate of 190 is far above any rates quoted anywhere
for encephalitis/encephalopathy after receipt of measles vaccine.
Considering the imprecision of the definition of "encephalitis" and
"encephalitic reaction" and the discrepancy of the rates, it is impossible
to interpret that report.

A report of adverse events associated with measles vaccine in Japan from
1978 to 1983 cited 12 cases of "encephalitis" or "encephalopathy," without
describing them, and derived a rate of 3.7 cases of "encephalitis'' per 1
million vaccinees administered the Schwarz vaccine and 2.9 cases per 1
million vaccinees administered the Biken-CAM vaccine (Hirayama, 1983). A
follow-up to that report published 5 years later (Isomura, 1988) mentioned
16 cases of "encephalitis" (4 more cases than the earlier report), but
provided no details. The incidence rate for "encephalopathy" and
"encephalitis" following measles vaccination appeared to be lower than the
observed incidence of encephalitis from all causes among age-matched
controls (Hirayama, 1983; Isomura, 1988). This comparison was not derived
from a controlled cohort study, however.

Measles Vaccine-Containing Preparations In an analysis of 433 spontaneous
reports to a vaccine manufacturer in the Federal Republic of Germany
(former West Germany) between 1976 and 1989 (Fescharek et al., 1990), 6 of
16 reports of "meningitis" or "encephalitis" were thought by the authors to
be possibly related to measles, measles-mumps, or measles-mumps-rubella
vaccine, leading to a rate of 1 case per 1 million doses distributed, as
calculated by the authors. The vaccine strains are those currently licensed
in the United States, that is, the more attenuated measles vaccine and
Jeryl Lynn mumps vaccine. Assuming that all 16 reports of cases of
"meningitis'' and "encephalitis" were causally related to the vaccine, the
rate would increase to about 3 cases per 1 million doses distributed, which
is within the range reported in other countries, as described above.

A study based on a new passive surveillance system in Canada reported a
rate of 1.1 cases of meningitis or encephalitis, without distinguishing
between the two, per 100,000 doses of MMR (Koch et al., 1989). (This high
rate was probably due to the inclusion of meningitis in the survey.) It was
estimated that more than 8 million doses of MMR were distributed in Canada
during the reporting period.

A description of 212 adverse events associated with MMR reported to Swedish
health authorities from 1982 to 1984 (when an estimated 700,000 doses of
MMR were sold) includes 17 reports of transient, serious cases of
neurologic symptoms: 3 patients with "encephalitic symptoms" who were
treated at the hospital, 7 patients with "encephalitic symptoms" who were
not hospitalized, 5 patients with acute symptoms with motor difficulties, 1
patient with seizures and fever, and 1 patient with hemiparesis (Taranger
and Wiholm, 1987). "Encephalitic symptoms" included tiredness, whining,
irritability, and mood changes with or without fever. No mention of CSF
pleocytosis was made. Follow-up of at least 1 year showed that one
18-month-old boy who had developed symptoms of mild encephalitis with
balance problems had residua of foot dragging and stumbling when he was tired.

Case Reports Many case reports describe encephalitis or encephalopathy
following administration of measles vaccine. Because isolation of measles
virus is problematic and exposure to wild-type measles virus is common, it
is difficult to assess a possible role of measles or measles vaccine in the
occurrence of encephalopathy or encephalitis in an individual case. Typical
case reports follow.

A 5-year-old received a live measles vaccine and developed fever two weeks
later (Alves et al., 1992). Three days after the onset of fever, the boy
presented with hemiparesis, dysarthria, and a generalized rigid-akinetic
syndrome. A spinal tap obtained four days later showed pleocytosis. One
month later he was diagnosed with postencephalitic parkinsonism. He
responded to levodopa therapy. The parkinsonism persisted for the 2 years
between the time of vaccination and publication of the report (Alves et
al., 1992). A 14-month-old girl received the wellcome measles vaccine and
developed convulsions 12 days later (Barbor and Grant, 1969). She became
confused, restless, and then unconscious. Although the authors called this
an encephalitis, there was no CSF pleocytosis on days 13 or 21
postvaccination. She made little progress in the 4 months between
hospitalization and publication of the report. An electroencephalographic
record of slow waves, which are not characteristic of measles encephalitis,
and possible slight head trauma 9 days after vaccination suggested a
temporal, not a causal, relation between the convulsions and the measles
vaccination. A 13-month-old girl was admitted to the hospital with
involuntary jerking movements of her limbs 10 days after receiving a
further attenuated Enders live measles vaccine (Jagdis et al., 1975). She
was afebrile, although she had fever for 2 days prior to admission. The CSF
was turbid and showed pleocytosis. She had a convulsion followed by apnea.
She died 13 days after vaccination. Postmortem examination suggested viral
encephalitis; Cowdry type A inclusion bodies suggested measles virus as the
etiologic agent, but no measles virus was isolated. She had no known
exposure to wild-type measles virus, but an epidemic in the community was
ending. Haun and Ehrhardt (1973) described a boy age 11 months who
developed drowsiness, convulsions, and coma 12 days following vaccination
with the L-16 SSW measles vaccine (a variant derived from the Soviet strain
Leningrad-16). There was pleocytosis in the CSF. He died the same day as
onset of symptoms. Autopsy findings were suggestive of disseminated
intravascular coagulation as the cause of death. A boy age 2 years was
administered live measles vaccine 10 days before the development of
persistent convulsions (Starke et al., 1970). The child suffered
convulsions accompanied by unconsciousness until his death a month later.
He had experienced convulsions in the first year of life during a bout of
pneumonia. The autopsy stated there was CNS death, "encephalitis" following
measles inoculation, and septic pulmonary infarction. No further details
are given.

Several reports of encephalopathy following measles vaccination can be
found in the Vaccine Adverse Event Reporting System (VAERS) (submitted
between November 1990 and July 1992). As with many VAERS reports, the
information that is supplied is frequently inadequate to support or reject
a diagnosis or to exclude the possibility that other factors are
responsible for the disorder, if the case was encephalopathy or
encephalitis. The committee found that 17 VAERS reports were suggestive of
encephalopathy or encephalitis in vaccinees (mostly MMR) from ages 5 months
to 16 years. Reported latencies ranged from 1 to 14 days after
immunization. The patients presented with symptoms such as fever, ataxia,
somnolence, convulsions, and flaccid paralysis. Several reports contained
too little information to suggest a diagnosis or to shed light on causality.

A specific type of measles encephalopathy, immunosuppressive measles
encephalopathy (IME), has been documented in two immunosuppressed children
following vaccination against measles. IME is distinct from acute measles
encephalitis and subacute sclerosing panencephalitis. It has an incubation
period of 5 weeks to 6 months. In one case of a 7-year-old girl with acute
lymphoblastic leukemia (Valmari et al., 1987), measles virus was isolated
from her CSF approximately 10 weeks after she received MMR (which contains
the more attenuated measles vaccine used in the United States). The authors
believed the isolated virus was vaccine strain rather than the wild-type
strain because the child had no contact with natural measles during the 5
weeks to 6 months prior to the onset of symptoms. A previously described
case of IME in a leukemic child involved the Schwarz strain vaccine virus
(Mitus et al., 1962). Measles virus was cultured from throat and
conjunctiva, but not from postmortem brain tissue.

Controlled Observational Studies
The National Childhood Encephalopathy Study, a case-control study described
in detail in Chapter 5, reported a significant association between measles
vaccination and onset of either convulsions or encephalopathy within 7 to
14 days of receiving the vaccine (Alderslade et al., 1981). However, a
separate analysis of those diagnosed with encephalitis or encephalopathy
was not performed

Controlled Clinical Trials
A report from India (Kumar et al., 1982) described 206 children injected
with the Schwarz strain of measles vaccine and 206 children who were not
immunized. A 14-month-old girl was diagnosed with encephalitis (fever,
vomiting, semi-consciousness, weakness, occasional white blood cells in the
CSF) on postvaccination day 10. At the time the report was published, she
was reported to be recovering "gradually." There were no cases of
encephalitis in the controls, but the numbers are far too small to detect
an association.

Causality Argument
There is demonstrated biologic plausibility that measles vaccine might
cause encephalopathy. Although there are a number of reports of
encephalitis or encephalopathy following immunization with measles vaccines
of various strains, the rates quoted are impossible to distinguish from
background rates. Good case-control or controlled cohort studies of these
conditions in similar unvaccinated populations, which are necessary for
determining the causal relation between measles and mumps and
encephalopathy and encephalitis, are lacking. No conclusive evidence of the
occurrence of encephalopathy or encephalitis resulting from the
administration of measles vaccine was identified. There are no data
regarding the occurrence of encephalopathy following administration of
monovalent mumps vaccine. It is therefore not possible to implicate
specifically either the measles or mumps component of MMR.

The evidence is inadequate to accept or reject a causal relation between
measles or mumps vaccine and encephalitis or encephalopathy.