Immunogenicity of second dose measles-mumps-rubella (MMR)
vaccine and implications for serosurveillance.
Pebody RG, Gay NJ, Hesketh LM, Vyse A, Morgan-Capner P, Brown DW, Litton P,
Miller E.
Sero-Epidemiology Unit, Immunisation Division, PHLS Communicable Disease
Surveillance Centre, 61 Colindale Avenue, London, UK. rpebody@phls.org.uk
Measles and mumps, but not rubella,
outbreaks have been reported amongst populations highly vaccinated with a
single dose of measles-mumps-rubella (MMR) vaccine. Repeated experience
has shown that a two-dose regime of measles vaccine is required to eliminate
measles. This paper reports the effect of the first and second MMR doses on
specific antibody levels in a variety of populations.2-4 years after receiving
a first dose of MMR vaccine at age 12-18 months, it was found that a large
proportion of pre-school children had measles (19.5%) and mumps (23.4%) IgG
antibody below the putative level of protection. Only a small proportion
(4.6%) had rubella antibody below the putative protective level. A total of
41% had negative or equivocal levels to one or more antigens. The proportion
measles antibody negative (but not rubella or mumps) was significantly higher
in children vaccinated at 12 months of age than at 13-17 months. There was no
evidence for correlation of seropositivity to each antigen, other than that
produced by a small excess of children (1%) negative to all three antigens.
After a second dose of MMR, the proportion negative to one or more antigens
dropped to <4%. Examination of national serosurveillance data, found that
following an MR vaccine campaign in cohorts that previously received MMR, both
measles and rubella antibody levels were initially boosted but declined to
pre-vaccination levels within 3 years.Our study supports the policy of
administering a second dose of MMR vaccine to all children. However, continued
monitoring of long-term population protection will be required and this study
suggests that in highly vaccinated populations, total measles (and rubella)
IgG antibody levels may not be an accurate reflection of protection. Further
studies including qualitative measures, such as avidity, in different
populations are merited and may contribute to the understanding of MMR
population protection.
Outbreak of influenza in
highly vaccinated crew of U.S.
Navy ship.
Earhart KC, Beadle C, Miller LK, Pruss MW, Gray GC, Ledbetter EK, Wallace
MR.
Naval Medical Center San Diego, San Diego, California 92134, USA. kcearhart@nmcsd.med.navy.mil
An outbreak of influenza A (H3N2)
occurred aboard a U.S. Navy ship in February 1996, despite 95% of the crew's
having been appropriately vaccinated. Virus isolated from ill crew
members was antigenically distinct from the vaccination strain. With an attack
rate of 42%, this outbreak demonstrates the potential for rapid spread of
influenza in a confined population and the impact subsequent illness may have
upon the workplace.
[Genetic evolution under vaccine pressure: the Bordetella
pertussis model]
[Article in French]
Simondon F, Guiso N.
Unite de recherche sur les maladies infectieuses et parasitaires, IRD (ex-ORSTOM),
Montpellier, France.
A possible genetic selective pressure related to the long-term use of vaccines
has been the object of recent theoretical thought and publications. For more
than thirty years, an effective vaccine has been in use against whooping cough
on a wide scale basis in several countries. Thus, the Bordetella pertussis
model may contribute to the analysis of an evolutionary risk linked to the
vaccine. To maintain and improve the control of whooping cough, better
vaccination coverage must be achieved in countries where prevalence is low. In
countries where high vaccination coverage has been achieved over a long
period, a trend toward the resurgence of the disease has been observed.
Efforts are therefore now being directed toward primary vaccination and
boosters. These two targets require new vaccines with fewer side effects.
Outbreaks in highly vaccinated
populations have been reported, raising the issues of vaccine efficacy, of the
long-term effect of vaccines on the transmission of the disease, and of
genetic selective pressure. Time trend modifications of circulating
strains related to vaccination practices and vaccine types have been observed
and are compatible with a selective pressure of the vaccine on related
pathogens. However, evidence for a causal relation is lacking. In order to
monitor and understand the various effects the vaccine may be having on the
effectiveness of immunisation against whooping cough, further surveillance is
needed, integrating a standardised characterisation of circulating strains and
vaccines by way of a space-time sampling model.
Varicella outbreaks after vaccine licensure: should they
make you chicken?
Buchholz U, Moolenaar R, Peterson C, Mascola L.
Epidemic Intelligence Service, Epidemiology Program Office, Centers for
Disease Control and Prevention, Atlanta, GA 30333, USA. ubuchholz@dhs.co.la.ca.us
In 1998, 3 years after vaccine licensure, child care centers (CCC) in Los
Angeles County continued to report varicella outbreaks. We investigated
outbreaks at 2 CCCs to determine the cause for them, such as low vaccination
coverage levels or unexpected low vaccine effectiveness. We collected
information on past history of varicella, illness during the outbreak, and
prior varicella vaccination among CCC attendees. We found that CCC "H" had a
vaccination coverage of 87% (34/39) compared with 30% (6/20) in CCC "L." The
overall attack rate was lower in CCC "H" (31%) than in "L" (61%; P value
=.03). Vaccine effectiveness for any varicella was 71% in "H" and 100% in "L."
Vaccinated children with varicella had milder disease than unvaccinated.
In conclusion, we found
varicella outbreaks in CCCs
with both high and low vaccination coverage. Vaccine effectiveness was within
the range predicted by the literature. Vaccination led to a lower
attack rate in the highly vaccinated CCC and appeared to protect from severe
disease.
During August 10-November 23, 1998, 33 confirmed measles cases were reported
to the Anchorage Department of Health and Human Services and the Alaska
Department of Health and Social Services (ADHSS). Of these, 26 cases were
confirmed by positive rubeola IgM antibody test, and seven met the clinical
case definition. This was the largest outbreak of measles in the United States
since 1996. This report summarizes results of the epidemiologic investigation
conducted by ADHSS and underscores the importance of second-dose requirements
for measles vaccine.
Department of Infectious and Tropical Diseases, London School of Hygiene and
Tropical Medicine, Keppel Street, London, UK. f.cutts@lshtm.ac.uk
The accelerating progress in reducing measles incidence and mortality in many
parts of the world has led to calls for its global eradication during the next
10-15 years. Three regions have established goals of elimination of indigenous
transmission of measles. The strategy used in the Americas of a mass 'catchup'
campaign of children 9 months to 15 years of age, high coverage through
routine vaccination of infants, intensive surveillance and follow-up campaigns
to prevent excessive build-up of susceptibles has had great success in
reducing measles transmission close to zero. However, while these developments
are impressive, much remains to be done to reduce measles-associated mortality
in western and central Africa, where less than half of children are currently
receiving measles vaccine and half a million children die from measles each
year.The obstacles to global measles eradication are perceived to be
predominantly political and financial. There are also technical questions,
however. These include the refinement of measles elimination strategies in the
light of recent outbreaks in the Americas; the implications of the HIV
epidemic for measles elimination, issues around injection safety, and concerns
about the possibility that secondary vaccine failures will contribute in
sustaining transmission in highly vaccinated populations. The global
priorities are to improve measles control in low income countries, increase
awareness among industrialized countries of the importance of measles, and
conduct studies to answer the technical questions about measles elimination
strategies.
Measles antibody levels in a vaccinated population in
Brazil.
Cox MJ, Azevedo RS, Massad E, Fooks AR, Nokes DJ.
Department of Biological Sciences, University of Warwick, Coventry, UK.
An epidemiological study of measles-specific immunoglobulin G antibody levels
was conducted using a representative sample of a vaccinated suburban
population in Sao Paulo State, Brazil. The study aimed to determine immunity
status in relation to age and infection or vaccination experience. 549
age-structured samples of sera, collected in 1990, were screened and
calibrated to the international reference serum, using measles nucleoprotein
in an enzyme immunoassay. In the age group with direct experience of
vaccination (9 months to 15 years), whether routine or campaign, over 90% had
detectable antibody > or = 50 miu/mL. However, 14% of these had antibody
concentrations between 50 and 100 miu/mL and 30% between 50 and 255 miu/mL. In
those over 15 years of age, 94% had antibody levels > 255 miu/mL, assumed to
be the result of past infection. The
study suggested that, within highly vaccinated populations, a proportion of
individuals had measles antibody levels which may be insufficient to protect
against reinfection or clinical disease. The implications of these
results, and similar findings elsewhere, in relation to the persistence of
measles requires investigation; this has particular relevance in Sao Paulo
following the recent measles outbreak.
Pertussis is increasingly recognized as a disease that affects older children
and adults, including fully vaccinated persons. This report describes a
statewide outbreak of pertussis in Vermont (1995 population: 584,771) in 1996
in a highly vaccinated population, affecting primarily school-aged children
and adults, and underscores the need to include pertussis in the differential
diagnosis of cough illness in persons of all ages.
Outbreak of measles in a
highly vaccinated secondary
school population.
Sutcliffe PA, Rea E.
Community Medicine Residency Program, University of Toronto, Ont.
OBJECTIVE: To examine the factors associated with measles vaccine
effectiveness and the effect of two doses of vaccine on measles susceptibility
during an outbreak. DESIGN: Retrospective cohort study. SETTING: A secondary
school in the City of Toronto. SUBJECTS: The entire school population (1135
students 14 to 21 years of age). MAIN OUTCOME MEASURES: Risk of measles during
an outbreak associated with age at first measles vaccination, length of time
since vaccination, vaccination before 1980 and whether date of vaccination was
estimated; vaccine efficacy of one dose versus two doses. RESULTS:
Eighty-seven laboratory-confirmed or clinically confirmed cases of measles
were identified (for an attack rate of 7.7%). The measles vaccination rate was
94.2%, and 10% of the students had received two doses of measles vaccine
before the outbreak. Among those who had received only one dose of vaccine,
vaccination at less than 15 months of age was associated with vaccine failure
(relative risk 3.62, 95% confidence interval 2.32 to 5.66). There was no
increased risk of vaccine failure associated with length of time since
vaccination once the relative risk was adjusted for age at vaccination in a
stratified analysis. Vaccination before 1980 and an estimated date of
vaccination were not associated with increased risk of vaccine failure.
Administration of a second dose of vaccine during the outbreak was not
protective. Two doses of vaccine given before the outbreak conferred
significant protection, and the relative risk of failure after one dose versus
two doses was 5.0 (95% confidence interval 1.25 to 20.15). Of the 87 cases, 76
(87%) could have been prevented had all the students received two doses of
measles vaccine before the outbreak, with the first at 12 months of age or
later. CONCLUSIONS: Delayed primary measles vaccination (at 15 months of age
or later) significantly reduced measles risk at later ages. However, revising
the timing of the current 12-month dose would leave children vulnerable during
a period in which there is increased risk of complications. The findings
support a population-based two-dose measles vaccination strategy for optimal
measles control and eventual disease elimination.
PMID: 8943928 [PubMed - indexed for MEDLINE]
AN: 97099351
Note: This presupposes that re-vaccination works
not only in the short-term, but in the long-term. Unfortunately, there is
evidence that re-vaccination does not work in the long-term. Even
Dr. Samuel Katz, the inventor of the
measles vaccine, has admitted as much. (More links will be provided as
time permits.) - SM
Of the 5551 confirmed measles cases reported in 1995 in the Americas, 2301
(41%) occurred in Canada. In this issue (see pages 1407 to 1413) Drs. Penny A.
Sutcliffe and Elizabeth Rea describe a measles outbreak that occurred during
that year in a highly vaccinated
secondary school population in Toronto. Their findings support the use
of a two-dose measles vaccination strategy. In this editorial the author
explains how a two-dose strategy lowers the incidence of primary and secondary
vaccine failures and thus reduces the number of susceptible people to below
the outbreak threshold. Two-dose programs in Finland, Sweden and the United
States have dramatically reduced the incidence rates of measles in those
countries, and it is expected that the implementation of two-dose programs and
"catch-up" campaigns in Canada and the remaining countries of the Americas
will eliminate measles from the Western Hemisphere by the year 2000.
Mumps outbreak in a
highly vaccinated school population. Evidence for large-scale
vaccination failure.
Cheek JE, Baron R, Atlas H, Wilson DL, Crider RD Jr.
Division of Field Epidemiology, Centers for Disease Control and Prevention,
Atlanta, GA, USA.
OBJECTIVES: To describe an outbreak and to identify risk factors for mumps
occurring in a highly vaccinated high school population. (Note: Highly
vaccinated means a population in which more than 95% have been vaccinated.)
DESIGN AND PARTICIPANTS: Survey and cohort study of 307 (97%) of 318 students.
OUTCOME MEASURES: Mumps was defined as an illness with 2 or more days of
parotid swelling. Serologic confirmation of infection was obtained in eight
cases, seven of which were evaluated for presence of IgM antibody using
immunofluorescent antibodies. Vaccination records were verified for 297 (97%)
students. RESULTS: Between October 3 and November 23, 1990, clinical mumps
developed in 54 students (attack rate, 18%), 53 of whom had been vaccinated.
Most cases (40 [77%] of 52) occurred 12 to 20 days after a school-wide pep
rally. Immunofluorescent antibody testing of all seven specimens demonstrated
IgM antibody to mumps. Risk factors for clinical mumps identified in
multivariate analyses included female gender (odds ratio, 3.0; 95% confidence
interval, 1.6 to 5.7) and source of vaccination other than the local public
health clinic (students vaccinated by private providers [odds ratio, 3.0; 95%
confidence interval, 1.3 to 5.2] or in other districts [odds ratio, 2.4; 95%
confidence interval, 1.1 to 5.3]). CONCLUSIONS:
The overall attack rate is the highest
reported to date (and to our knowledge) for a population demonstrating
virtually complete mumps vaccine coverage. Even verified documentation of
vaccination may not be an accurate indicator of an individual's protection
against mumps. Vaccination failure may play an important role in contemporary
mumps outbreaks. We found no evidence to indicate that waning immunity
(secondary vaccine failure) contributed significantly to this outbreak. A
second dose of mumps vaccine, as recommended using measles-mumps-rubella
vaccine, could potentially prevent similar outbreaks in secondary school
populations in the future.
Outbreaks in highly
vaccinated populations: implications for studies of vaccine
performance.
Fine PE, Zell ER.
Immunization Division, Centers for Disease Control and Prevention, Atlanta, GA
30333.
Most of the factors associated with the failure of a vaccination to provide
protective immunity are not distributed uniformly or randomly within
populations. This paper explores the extent to which a nonrandom distribution
of vaccination failures and the selection of exceptional situations for
investigation may influence estimates of vaccine performance. The authors show
that outbreak investigations will tend to underestimate vaccination efficacy,
and that the extent of underestimation will be related directly to the size of
the epidemic triggering an investigation, the vaccination coverage in the
community, and the extent of clustering of vaccination failures in the
population; it will be related inversely to the size of and contact intensity
within the investigated community. These potential sources of bias are not the
only problems that arise in estimating vaccine efficacy, but they should be
taken into consideration when analyzing and interpreting outbreak situations.
The fact that outbreak investigations carried out within the United States
during the past decade have provided estimates of measles vaccination efficacy
on the order of 95% is consistent with a somewhat higher overall "true"
efficacy of current vaccines and procedures in the total population. It is
important to understand better the frequency, distribution, and risk factors
for vaccination failures in populations.
Hersh BS, Fine PE, Kent WK, Cochi SL, Kahn LH, Zell ER, Hays PL, Wood CL.
Division of Immunization, Centers for Disease Control, Atlanta, Georgia 30033.
From October 1988 to April 1989, a large mumps outbreak occurred in Douglas
County, Kansas. Of the 269 cases, 208 (77.3%) occurred among primary and
secondary school students, of whom 203 (97.6%) had documentation of mumps
vaccination. Attack rates were highest for students attending junior high
school (8.0%), followed by high school (2.0%) and elementary school (0.7%). A
retrospective cohort study conducted at one junior high school with an attack
rate of 12.9% did not find age at vaccination or type of vaccine received
(single or combined antigen) to be risk factors for vaccine failure.
Students vaccinated more than 4 years
before the outbreak appeared to have a higher attack rate than those
vaccinated more recently (relative risk (RR) = 4.3; 95% confidence
interval (CI) = 0.6, 30.0); however, this association did not exist when risk
was evaluated based on number of vaccine doses received.
Students who had documentation of
receiving only one dose of vaccine were at greater risk than those who had
received two doses (RR = 5.2;
95% CI = 1.0, 206.2). Overall, vaccine effectiveness among Douglas
County junior high school students was estimated to be 83% (95% CI = 57%,
94%). These data suggest that mumps
vaccine failure and the failure to vaccinate have contributed to the relative
resurgence of mumps observed in the United States since 1986. The recent
change in immunization policy to recommend a two-dose schedule of
measles-mumps-rubella vaccine should help reduce the occurrence of mumps
outbreaks in highly vaccinated populations.
Measles control in the United States: problems of the past
and challenges for the future.
Wood DL, Brunell PA.
Ahmanson Department of Pediatrics, Cedars-Sinai Medical Center, Los Angeles,
California 90048, USA.
Elimination of indigenous measles from the United States has been a public
priority since 1978. To assess the progress made toward this goal, we review
the epidemiology of measles from 1963 to the present.
From the 1970s through early into the
recent measles epidemic, the majority of measles cases were in highly
vaccinated, school-age children. This was due primarily to a 1 to 5% primary
measles-mumps-rubella vaccine failure rate and nonrandom mixing patterns among
school-age populations. To eliminate susceptible individuals in the
school-age populations, a second dose of measles vaccine is now recommended
between 5 and 6 years or 11 and 12 years by both the Advisory Committee on
Immunization Practices and the American Academy of Pediatrics. Later in the
epidemic, measles cases surged among unimmunized preschool children,
especially among the poor in inner-city areas. Immunization rates have been
documented to be low among preschool populations because of missed
opportunities to administer vaccines at all health visits and barriers to
access to immunizations. To raise immunization rates, the age for the first
measles-mumps-rubella immunization was lowered to 12 to 15 months of age,
federal immunization funding has increased, and new standards for immunization
delivery have been developed and promulgated.
Division of Field Epidemiology, Centers for Disease Control and Prevention,
Atlanta, Georgia.
From January to July 1991, an outbreak of mumps occurred in Maury County,
Tennessee. At the primarily affected high school, where 98% of students and
all but 1 student with mumps had been vaccinated before the outbreak, 68 mumps
cases occurred among 1116 students (attack rate, 6.1%). Students vaccinated
before 1988 (the first year mumps vaccination was required for school
attendance in Tennessee) may have been at greater risk of mumps than those
vaccinated later (65[6.1%] of 1001 vs. 2[2.2%] of 89; risk ratio, 2.9; 95%
confidence interval, 0.7-11.6). Of 13 persons with confirmed mumps who
underwent serologic testing, 3 lacked IgM antibody in well-timed acute- and
convalescent-phase serum specimens. Vaccine
failure accounted for a sustained mumps outbreak in a highly vaccinated
population. Most mumps cases were attributable to primary vaccine failure. It
is possible that waning vaccine-induced immunity also played a role.
A measles outbreak at a college with a prematriculation
immunization requirement.
Hersh BS, Markowitz LE, Hoffman RE, Hoff DR, Doran MJ, Fleishman JC,
Preblud SR, Orenstein WA.
Division of HIV/AIDS, Centers for Disease Control, Atlanta, GA 30333.
BACKGROUND. In early 1988 an outbreak of 84 measles cases occurred at a
college in Colorado in which over 98
percent of students had documentation of adequate measles immunity
(physician diagnosed measles, receipt of live measles vaccine on or after the
first birthday, or serologic evidence of immunity) due to an immunization
requirement in effect since 1986. METHODS. To examine potential risk factors
for measles vaccine failure, we conducted a retrospective cohort study among
students living in campus dormitories using student health service vaccination
records. RESULTS. Overall, 70 (83 percent) cases had been vaccinated at
greater than or equal to 12 months of age. Students living in campus
dormitories were at increased risk for measles compared to students living
off-campus (RR = 3.0, 95% CI = 2.0, 4.7). Students vaccinated at 12-14 months
of age were at increased risk compared to those vaccinated at greater than or
equal to 15 months (RR = 3.1, 95% CI = 1.7, 5.7). Time since vaccination was
not a risk factor for vaccine failure. Measles vaccine effectiveness was
calculated to be 94% (95% CI = 86, 98) for vaccination at greater than or
equal to 15 months. CONCLUSIONS. As in
secondary schools, measles outbreaks can occur among highly vaccinated college
populations. Implementation of recent recommendations to require two doses of
measles vaccine for college entrants should help reduce measles outbreaks in
college populations.
An outbreak of whooping cough in a
highly vaccinated urban
community.
Strebel P, Hussey G, Metcalf C, Smith D, Hanslo D, Simpson J.
Centre for Epidemiological Research, South African Medical Research Council,
Tygerberg.
In 1950 a whole-cell pertussis vaccine was introduced in Cape Town and was
followed by a marked decline in reported whooping cough mortality and
morbidity. This resulted in reduced awareness of whooping cough as a clinical
problem and, in recent years, no routine diagnostic tests for Bordetella
pertussis have been performed. An outbreak of whooping cough occurred in Cape
Town between 1 June 1988, and 31 May 1989, with 292 children admitted to
hospital for whooping cough during this period (hospital admission rate in
children under 5 years of age = 187 per 100,000). In an investigation of 239
children attending four pre-primary schools in the city, the whooping cough
attack rate was 33 per cent, while pertussis vaccine coverage was 95 per cent.
In the latter part of the outbreak nasopharyngeal swabs and serology were
performed in patients presenting to a children's hospital with suspected
whooping cough. Bordetella pertussis was isolated from 3 out of 34 (9 per
cent) children tested and the first isolate was serotyped as type 1,2,4.
Available clinical and laboratory evidence indicated that the organism
responsible for the outbreak was Bordetella pertussis.
Coverage studies for pertussis vaccine
in Cape Town indicated that between 81 and 93 per cent of children were fully
immunized by 13 months of age. These findings suggest that, since its
introduction, the whole-cell pertussis vaccine produced in South Africa has
been highly effective in controlling whooping cough. However, it was not able
to prevent a moderate scale outbreak, even in the presence of high vaccination
levels.
Department of Pediatrics, University of Wisconsin, Madison 53792.
A prolonged school-based outbreak of measles provided an opportunity to study
"vaccine-modified" mild measles and secondary vaccine failure. Thirty-six
(97%) of 37 unvaccinated patients had rash illnesses that met the Centers for
Disease Control clinical case definition of measles, but 29 (15%) of 198
vaccinated patients did not, primarily because of low-grade or absent fever.
Of 122 patients with seroconfirmed measles, 10 patients (all previously
vaccinated) had no detectable measles-specific IgM and significantly milder
illness than either vaccinated or unvaccinated patients with IgM-positive
serum. Of 108 vaccinated patients with seroconfirmed measles, 17 patients
(16%) had IgM-negative serology or rash illnesses that failed to meet the
clinical case definition; their mean age (13 years), age at the time of
vaccination, and time since vaccination did not differ from those of other
vaccinated patients. The occurrence of
secondary vaccine failure and vaccine-modified measles does not appear to be a
major impediment to measles control in the United States but may lead to
underreporting of measles cases and result in overestimation of vaccine
efficacy in highly vaccinated populations.
An explosive point-source measles outbreak in a
highly vaccinated population.
Modes of transmission and risk factors for disease.
Chen RT, Goldbaum GM, Wassilak SG, Markowitz LE, Orenstein WA.
Division of Immunization, Centers for Disease Control, Atlanta, GA.
In 1985, 69 secondary cases, all in one generation, occurred in an Illinois
high school after exposure to a vigorously coughing index case. The school's
1,873 students had a pre-outbreak vaccination level of 99.7% by school
records. The authors studied the mode of transmission and the risk factors for
disease in this unusual outbreak. There were no school assemblies and little
or no air recirculation during the schooldays that exposure occurred. Contact
interviews were completed with 58 secondary cases (84%); only 11 secondary
cases (19%) of these may have had exposure to the index case in the
classrooms, buses, or out of school. With the use of the Reed-Frost epidemic
model, only 22-65% of the secondary cases were likely to have had at least one
person-to-person contact with the index case during class exchanges,
suggesting that this mode of transmission alone could not explain this
outbreak. A comparison of the first 45 cases and 90 matched controls suggested
that cases were less likely than controls to have provider-verifiable school
vaccination records (odds ratio (OR) = 8.1) and more likely to have been
vaccinated at less than age 12 months (OR = 8.6) or at age 12-14 months (OR =
7.0). Despite high vaccination levels,
explosive measles outbreaks may occur in secondary schools due to 1) airborne
measles transmission, 2) high contact rates, 3) inaccurate school vaccination
records, or 4) inadequate immunity from vaccinations at younger ages.
Division of Immunization, Centers for Disease Control, Atlanta, GA 30333.
Since the licensing of measles vaccine in 1963, the incidence of reported
measles in the United States has declined to less than 2 percent of previous
levels. To characterize the current epidemiology of measles in the United
States, we analyzed measles outbreaks that occurred during 1985 and 1986.
There were 152 outbreaks (defined as five or more cases related
epidemiologically), which accounted for 88 percent of the cases reported
during those two years. There were two major types of outbreaks: those in
which most of the cases occurred among preschool-age children (those under 5
years of age) (26 percent) and those in which most of the cases occurred among
school-age persons (those 5 to 19 years of age) (67 percent). The outbreaks
among preschool-age children ranged in size from 5 to 945 cases (median, 13);
a median of only 14 percent of the cases occurred in vaccinated persons, and a
median of 45 percent of the cases were classified as preventable according to
the current strategy. Outbreaks among
school-age persons ranged in size from 5 to 363 cases (median, 25); a median
of 60 percent of the cases occurred in vaccinated persons, and a median of
only 27 percent of the cases were preventable. The outbreaks among
preschool-age children indicate deficiencies in the implementation of the
national measles-elimination strategy. However, the extent of measles
transmission among highly vaccinated school-age populations suggests that
additional strategies, such as selective or mass revaccination, may be
necessary to prevent such outbreaks.
Measles outbreak in a vaccinated school population:
epidemiology, chains of transmission and the role of vaccine failures.
Nkowane BM, Bart SW, Orenstein WA, Baltier M.
An outbreak of measles occurred in a high school with a
documented vaccination level of 98 per
cent. Nineteen (70 per cent) of the cases were students who had
histories of measles vaccination at 12 months of age or older and are
therefore considered vaccine failures. Persons who were unimmunized or
immunized at less than 12 months of age had substantially higher attack rates
compared to those immunized on or after 12 months of age. Vaccine failures
among apparently adequately vaccinated individuals were sources of infection
for at least 48 per cent of the cases in the outbreak. There was no evidence
to suggest that waning immunity was a contributing factor among the vaccine
failures. Close contact with cases of measles in the high school, source or
provider of vaccine, sharing common activities or classes with cases, and
verification of the vaccination history were not significant risk factors in
the outbreak. The outbreak subsided
spontaneously after four generations of illness in the school and demonstrates
that when measles is introduced in a highly vaccinated population, vaccine
failures may play some role in transmission but that such transmission is not
usually sustained.
Epidemic measles in a
highly vaccinated population.
Shasby DM, Shope TC, Downs H, Herrmann KL, Polkowski J.
During November, 1975, to May, 1976, measles occurred at a rate of 20.3 cases
per 1000 in a purported immunized population, of whom historical and serologic
survey revealed that 9 per cent had no history of either measles illness or
vaccination and 18 per cent did not have detectable measles antibody. Antibody
was detectable in 92 per cent of those vaccinated at greater than or equal to
13 months, 80 per cent at 12 months and 67 per cent of those vaccinated when
less than one year old (P less than 0.001), but no significant differences
existed with increasing years since vaccination (P greater than 0.1). A second
vaccination increased detectable antibody prevalence only in those originally
vaccinated when less than nine months old (42 to 80 per cent, P less than
0.02). During a measles outbreak, more cases occurred in those receiving
vaccine when less than 12 months old than in those vaccinated at greater than
or equal to 12 months (37 per cent vs. 9 per cent, P less than 0.001). A
second vaccination protected those originally vaccinated at less than 12
months (35 per cent ill without a second vaccination vs. 2 per cent with, P
less than 0.001). Thus, a single
measles vaccination of children less than 12 months old does not protect; a
second vaccination will protect this group.
Editorial Note: This outbreak
demonstrates that transmission of measles can occur within a school population
with a documented immunization level of 100%. This level was validated
during the outbreak investigation. Previous investigations of measles outbreaks
among highly immunized populations have revealed risk factors such as improper
storage or handling of vaccine, vaccine administered to children under 1 year of
age, use of globulin with vaccine, and use of killed virus vaccine (1-5).
However, these risk factors did not adequately explain the occurrence of this
outbreak.
ALL INFORMATION, DATA, AND
MATERIAL CONTAINED, PRESENTED, OR PROVIDED HERE IS FOR GENERAL INFORMATION
PURPOSES ONLY AND IS NOT TO BE CONSTRUED AS REFLECTING THE KNOWLEDGE OR OPINIONS
OF THE PUBLISHER, AND IS NOT TO BE CONSTRUED OR INTENDED AS PROVIDING MEDICAL OR
LEGAL ADVICE. THE DECISION WHETHER OR NOT TO VACCINATE IS AN IMPORTANT AND
COMPLEX ISSUE AND SHOULD BE MADE BY YOU, AND YOU ALONE, IN CONSULTATION WITH
YOUR HEALTH CARE PROVIDER.
