A measles outbreak at a college with a prematriculation immunization requirement.

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.     

School-based measles outbreaks: correlation of age at immunization with risk of disease.

During the Spring of 1978, students with a history of previous measles vaccination accounted for over three-forths of 203 cases of measles in a metropolitan county. Seventy cases occurred in two schools where 99% of the students were vaccinated. We analyzed countywide data to determine past patterns of measles vaccination, including outbreak control and vaccination update clinics. We also examined records of children from the two schools to assess the relationship between disease incidence and age at vaccination. When susceptibility was determined by trained health workers rather than by parents, fewer doses of measles vaccine were estimated to be needed. The majority of cases occurred among children 5 to 9 years old. Attack rates were higher for children vaccinated at 12 months of age or younger than for those vaccinated at 13 months of age or older. There were no significant differences in attack rates among children vaccinated at 13 months of age or older. These findings support recommendations for delaying routine measles vaccination until after 12 months of age and suggest that, during outbreaks, all children vaccinated prior to 13 months of age be revaccinated.     

A million dollar measles outbreak: epidemiology, risk factors, and a selective revaccination strategy.

Between February 8 and April 4, 1986, an outbreak of measles occurred in the State of Arkansas. A total of 489 suspected measles cases were reported from 53 counties; 86 schools statewide reported suspected measles cases. There were 284 cases confirmed in 18 counties; 23.6 percent among students in one university and 41.2 percent among students in kindergarten through 12th grade in 32 schools. An epidemiologic investigation was carried out to evaluate risk factors for vaccine failure and to assess the effectiveness of a selective revaccination strategy in the outbreak setting. A cohort study conducted at a junior high school showed that, compared with students vaccinated against measles at ages 15 months or older, those vaccinated at ages 12-14 months had a three-fold increased risk of measles (relative risk 3.2, 95 percent confidence interval 1.5, 6.9). For schools reporting measles, the Arkansas Department of Health and the Department of Education jointly required reimmunization of students vaccinated at ages younger than 15 months and the exclusion of students not vaccinated at ages 15 months or older until they were vaccinated or until 2 weeks after the last rash onset. To implement these recommendations, more than 100,000 doses of combined measles-mumps-rubella vaccine were distributed at a cost greater than $1 million.     

A cost-effectiveness analysis of measles outbreak control strategies

This study compares the cost-effectiveness of six vaccination strategies during a measles outbreak: vaccination of all susceptibles 15 months of age or older and born after 1956 (the current routine strategy); lowering the recommended age at vaccination from 15 to 12 months (plus current routine strategy); lowering the recommended age at vaccination to six months (plus current routine strategy); revaccination of those vaccinated at 12-14 months of age (plus current routine strategy); vaccination of all students in school regardless of immune status; and vaccination of all residents 15 months to 28 years of age in the community regardless of immune status. The analysis is based on the hypothetical, early application of these strategies to a 1985 measles outbreak in Montana, which occurred despite appropriate application of current prevention and control recommendations. Although the results are applicable only to this particular outbreak, this analysis provides an approach which can be used in other settings to assess measles outbreak control strategies. Similar studies would need to be performed in a variety of settings to determine the most cost-effective measles outbreak control strategies overall.     

Continuing measles transmission in students despite school-based outbreak control program

FRom September 9, 1981 to January 5, 1982, a measles outbreak occurred in Warren County, Pennsylvania. The outbreak persisted for nine weeks following the implementation of a county-wide outbreak control program primarily consisting of identifying and vaccinating susceptible schoolchildren. Forty-six cases occurred among students more than two weeks after control program implementation. All 46 had a school record indicating adequate measles vaccination; 13 had been vaccinated at control program clinics by one jet-injector team (Team A). A seroprevalence survey demonstrated that persons vaccinated by Team a had a significantly higher rate of vaccination failure than children vaccinated by other teams (37.0% vs. 5.9%, p = 5.7 X 10(-7). A case-control study was undertaken to assess possible additional risk factors for developing measles. Individuals with measles were nine times more likely than control individuals to have records of measles immunization that could not be verified with providers or to have been vaccinated at 12 months of age. The most likely reasons that this outbreak was sustained among persons with adequate vaccination histories were: 1) impotent vaccines and/or improper vaccine administration techniques were used by one jet-injector team; 2) several persons with histories of adequate vaccination were really not adequately vaccinated; adn 3) a substantial number of persons had been vaccinated at 12 months of age. There is no evidence from this outbreak that transmission of measles can be sustained among the 2-10% of individuals expected to remain susceptible following a single appropriate measles vaccination.     

Twice vaccinated recipients are better protected against epidemic measles than are single dose recipients of measles containing vaccine

OBJECTIVE: To study measles risk after revaccination. DESIGN: A population-based case-control study during an epidemic season. MAIN OUTCOME MEASURE: Relative serologically confirmed measles risk. PARTICIPANTS AND METHODS: 153 vaccinated cases, mostly from rural areas, were serologically confirmed as measles at the central laboratory in 1988-89. A randomly selected group of 453 controls from either municipalities of vaccinated cases or from areas where measles attack rate was > 600/10(5), was identified via the population registry. Vaccination and measles histories of cases and controls were determined from official vaccination cards. RESULTS: Once and twice vaccinated had crude relative risk 15.6 and 2.3 compared with thrice vaccinated. When cases who had received their first vaccination at less than 14 months of age were omitted from analysis, once vaccinated had 4.0 (95% CI 1.2, 16.6) times higher age adjusted measles risk compared with twice vaccinated. When, omission was extended to cases from one particular municipality where even revaccinees had high measles risk during an explosive outbreak the corresponding risk ratio was 17.8 (2.8, 67.8). CONCLUSIONS: Twice vaccinated have better protection against epidemic measles compared with single dose recipients.     

Measles outbreak in a vaccinated school population: epidemiology, chains of transmission and the role of vaccine failures

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.     

Risk for measles related to immunization status in two Tucson high schools

An outbreak of measles occurred in Tucson, AZ, in 1985; 112 of the 225 cases were among students at two large high schools. A review of the immunization records of all students at both schools was undertaken in order to assess the risk of a person contracting measles in relation to that person's immunization status. Two factors, the lack of an immunization record and immunization prior to 12 months of age, showed a positive association with contracting measles. The association was statistically significant at one high school but not the other. At the first high school, students who were immunized at 12 to 14 months of age had a greater risk of infection than those immunized at 15 months or older. However, age at immunization of 12 to 14 months was not associated with a significantly higher risk when persons with multiple doses of vaccine were excluded from the analysis. Students of both schools showed a lower attack rate for those who had received multiple doses of vaccine, but the difference was not statistically significant.     

A persistent outbreak of measles despite appropriate prevention and control measures

From January 4 to May 13, 1985, an outbreak of 137 cases of measles occurred in Montana and persisted for 12 generations of spread. A total of 114 cases occurred on the Blackfeet Indian reservation in northwest Montana. Of the 137 cases, 82 (59.9%) were in school-aged children (aged 5-19 years). Of the 114 cases on the reservation, 108 (94.7%) were classified as programmatically nonpreventable. A total of 64 (82.1%) of the 78 patients on the reservation who were born after 1956 and were above the recommended age at vaccination had a history of adequate measles vaccination. Additionally, an audit of immunization records at the schools in Browning, Montana, where most of the cases occurred, showed that 98.7% of students were appropriately vaccinated. A retrospective cohort study in the Browning schools failed to identify age at vaccination or time since vaccination as significant risk factors for vaccine failure. Overall vaccine efficacy was 96.9% (95% confidence interval = 89.5-98.2%). None of 80 Browning students who were vaccinated at less than 12 months of age and revaccinated at 15 months of age or older became infected. A case-control study showed a significant association between attendance at Browning basketball games and infection early in the outbreak. This outbreak suggests that measles transmission may persist in some settings despite appropriate implementation of the current measles elimination strategy.     

Measles outbreak in the Republic of the Marshall Islands, 2003

BACKGROUND: Measles is a highly contagious viral infection. Measles transmission can be prevented through high population immunity (>or=95%) achieved by measles vaccination. In the Republic of the Marshall Islands (RMI), no measles cases were reported during 1989-2002; however, a large measles outbreak occurred in 2003. Reported 1-dose measles vaccine coverage among children aged 12-23 months varied widely (52-94%) between 1990 and 2000. METHODS: RMI is a Pacific island nation (1999 population: 50,840). A measles case was defined as fever, rash, and cough, or coryza, or conjunctivitis, in an RMI resident between July 13 and November 7, 2003. A vaccination campaign was used for outbreak control. RESULTS: Of the 826 reported measles cases, 766 (92%) occurred in the capital (Majuro). There were 186 (23%) cases in infants aged <1 year and 309 (37%) of cases in persons aged >or=15 years. The attack rate was highest among infants (Majuro atoll: 213 cases/1,000 infants). Among cases aged 1-14 years, 281 (59%) reported no measles vaccination before July 2003. There were 100 hospitalizations and 3 deaths. The measles H1 genotype was identified. The vaccination campaign resulted in 93% coverage among persons aged 6 months to 40 years. Interpretation Populations without endemic measles transmission can accumulate substantial susceptibility and be at risk for large outbreaks when measles virus is imported. 'Islands' of measles susceptibility may develop in infants, adults, and any groups with low vaccine coverage. To prevent outbreaks, high population immunity must be sustained by maintaining and documenting high vaccine coverage.     

An explosive point-source measles outbreak in a highly vaccinated population. Modes of transmission and risk factors for disease

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.     

浙江省1999年麻疹暴发疫情特征分析

浙江省 1999年麻疹监测系统报告 10起麻疹暴发疫情 ,发病 475例 ,无死亡。农村和学校为主要发生地 ;最高罹患率171 6 0‰ ,同时存在城区流动人口聚集地的麻疹暴发 ,但是发病强度偏低 ;发病时间主要分布在 1～ 6月和 10月 ;暴发病例中有明确麻疹疫苗 (MV)接种史的占 13 1% ,无MV接种史的占 2 8 2 % ,MV接种史不详的占 5 8 7% ;<14岁儿童病例数占总病例数的91 1%。对于学校和城区型暴发 ,应急免疫措施效果相对较好。建议在切实提高常规免疫接种率的同时 ,对持续有麻疹暴发和计划免疫工作薄弱地区采取MV的强化免疫     

Challenges in managing a school‐based measles outbreak in Melbourne,Australia, 2014

Objective: To identify barriers to control of a Victorian primary school‐based measles outbreak. Methods: Confirmed measles cases notified in Victoria in 2014 were reviewed. Surveillance data, correspondence, and investigation notes for the school‐based outbreak were assessed regarding timeliness of diagnosis and notification, and adequacy of school‐based immunisation records. Results: Twenty‐three (31%) of the 75 measles cases notified in 2014 were school‐aged (5–18 years); three had documentation of measles vaccination, 17 were unvaccinated, and three had unknown vaccination history. Eight measles outbreaks were identified, including a primary school‐based outbreak with ten cases. Of the six unvaccinated pupils in the affected school, five (83%) contracted measles. The proportion of the school's prep students with documented vaccination records, as required by law, ranged from 39% in 2013 to 97% in 2014. Conclusions: Inadequately vaccinated students constitute a vulnerable population and schools are a potential site for measles outbreaks. Inadequate enforcement of school‐based immunisation records impact the management and control of school‐based measles outbreaks. Implications for Public Health: There is a need to educate clinicians on measles diagnosis and notification, and schools on the requirement to maintain up‐to‐date vaccination records. School entry is an opportunity to review student vaccination history and offer immunisations.     

Measles outbreak in a northern Pakistani village: epidemiology and vaccine effectiveness

In the spring of 1990, local community health workers reported a measles outbreak in several partially vaccinated villages in the Punial Valley in northern Pakistan. The authors conducted an investigation in one of these villages to assess vaccine coverage and vaccine efficacy and to describe the patterns of measles outbreaks that prevailed in this community. The results of a survey of the entire village revealed two major gaps in vaccine coverage: the small minority Sunni community and children over 3 years of age. Vaccine efficacy was estimated to range from 73 to 90% but was markedly reduced in children who were vaccinated under 12 months of age. The occurrence of an outbreak in a community in which a relatively new vaccination program is primarily directed at younger children has been predicted by theoretical models of measles dynamics and is consistent with the experience of other vaccination programs in the developing world. These observations suggest that, in some areas of the developing world, the age groups targeted to receive measles vaccinations may need to be broadened to ensure adequate coverage to prevent recurrent outbreaks.     

Measles vaccine efficacy during an outbreak in a highly vaccinated population: incremental increase in protection with age at vaccination up to 18 months.

During a large measles outbreak in Quebec City in 1989, two investigations conducted in parallel evaluated the relative risk of measles and measles vaccine effectiveness with respect to age at vaccination. The study was a school-based case-control study including 563 cases and 1126 classmate controls. The second was a cohort study of the siblings of school cases including 493 siblings aged between 1 and 19 years. The relative risks (RR) of measles were similar in both settings and the trend towards increased vaccine efficacy with increasing age at vaccination was highly significant (P < 0.001). Vaccine efficacy rose from 85% in children vaccinated at 12 months of age to > or = 94% in those vaccinated at 15 months and older. Even for children vaccinated at or after 18 months of age, the RR of measles was reduced when compared with children vaccinated between 15 and 17 months of age (RR 0.61, CI 95% 0.33-1.15). Small changes in the timing of initial measles vaccination can have a major impact on vaccine efficacy.     

2005～2009年北京市密云县麻疹流行病学分析

目的了解北京市密云县麻疹流行特点和流行现状,为消除麻疹提供科学依据。方法采用描述性流行病学方法对密云县2005～2009年确诊麻疹病例进行流行病学分析。结果 2005～2009年密云县累计发生麻疹病例127例,年平均发病率为5.24/10万。麻疹发病以散发和暴发并存,12月～次年5月为麻疹高发季节,占全年总病例数的88.98%;本地麻疹发病主要集中在1岁组和≥30岁年龄组,流动人口发病主要集中在15～30岁;共发生2起暴发疫情,均为外来人口较多的工厂。有麻疹疫苗免疫史的发病22例,占总病例数的20.56%;38例属于流动人口,89例为本地人口,流动人口与本地人口免疫史差异有统计学意义。结论 8月龄仍为麻疹防控的重点人群,城乡结合部和山区应切实做好外来务工人员麻疹疫苗接种工作,重点防控外来人口中的麻疹暴发疫情;对本地适龄成人进行麻疹疫苗强化免疫,提高成人麻疹疫苗接种率,加强成人麻疹的预防控制。     

Measles vaccine effectiveness in Central Australian Aboriginal children vaccinated at or after eight months of age

An outbreak of measles in central Australia in 1994 provided the first opportunity to evaluate the effectiveness of the measles vaccine given to Aboriginal children at nine months of age since 1984. Children eligible for the study that was conducted in one community in the region were aged between nine months and 10 years. Eight of the 109 eligible children developed measles. The only unvaccinated child also developed measles. Vaccination failures occurred in 7.8% (6/77) of children vaccinated between eight and 11 months of age and in 3.2% (1/ 31) vaccinated after 11 months of age. Overall vaccine effectiveness was 93.5%. The level of vaccine uptake in central Australia is high and the last region-wide outbreak before 1994 occurred in 1981-82. If the age of vaccination against measles is to be determined by the average age of infection; the age of vaccination should now be raised to 12 months of age; this is the age at which Aboriginal children in all other states and all children in Australia are vaccinated.     

Obstacles in measles elimination: an in-depth description of a measles outbreak in Ghent,Belgium, spring 2011

Background

From Mid-February to April 2011 one of the largest measles-outbreak in Flanders, since the start of the 2-dose vaccination scheme in 1995, took place in Ghent, Belgium. The outbreak started in a day care center, infecting children too young to be vaccinated, after which it spread to anthroposophic schools with a low measles, mumps and rubella vaccination coverage. This report describes the outbreak and evaluates the control measures and interventions.

Methods

Data collection was done through the system of mandatory notification of the public health authority. Vaccination coverage in the schools was assessed by a questionnaire and the electronic immunization database ‘Vaccinnet’. A case was defined as anyone with laboratory confirmed measles or with clinical symptoms and an epidemiological link to a laboratory confirmed case. Towards the end of the outbreak we only sought laboratory confirmation for persons with an atypical clinical presentation or without an epidemiological link. In search for an index patient we determined the measles IgG level of infants from the day care center.

Results

A total of 65 cases were reported of which 31 were laboratory confirmed. Twenty-five were confirmed by PCR and/or IgM. In 6 infants, too young to be vaccinated, only elevated measles IgG levels were found. Most cases (72%) were young children (0–9 years old). All but two cases were completely unimmunized. In the day care center all the infants who were too young to be vaccinated (N=14) were included as cases. Thirteen of them were laboratory confirmed. Eight of these infants were hospitalized with symptoms suspicious for measles. Vaccination coverage in the affected anthroposophic schools was low, 45-49% of the pupils were unvaccinated. We organized vaccination campaigns in the schools and vaccinated 79 persons (25% of those unvaccinated or incompletely vaccinated).

Conclusions

Clustering of unvaccinated persons, in a day care center and in anthroposophic schools, allows for measles outbreaks and is an important obstacle for the elimination of measles. Isolation measures, a vacation period and an immunization campaign limited the spread of measles within the schools but could not prevent further spread among unvaccinated family members. It was necessary to raise clinicians'' awareness of measles since it had become a rare, less known disease and went undiagnosed.     

The 1988-1989 measles epidemic in Hungary: assessment of vaccine failure.

Hungary has had a successful measles vaccination programme, achieving over 93% coverage in targeted groups. However, from September 1988 until December 1989, 17,938 measles cases were reported among the civilian population (attack rate [AR] = 169 per 100,000 population) with the majority of cases occurring in vaccinated people. National surveillance data were analysed to determine reasons for the outbreak and risk factors for vaccine failure. People born during 1971 and 1972 had been targeted for vaccination during campaigns in April and September of 1973 and had the highest AR (1332 and 1632 per 100,000, respectively). Epidemiological studies of vaccine efficacy conducted among secondary school students corroborated these findings. Among 754 secondary school students, those vaccinated during the April 1973 campaign were at highest risk compared with those vaccinated at routine health care after 1974 (relative risk = 10.9, 95% confidence interval [Cl]: 2.5-47.9). Among 341 primary school students, one-dose recipients were at higher risk compared with two-dose recipients controlling for age at and time elapsed since vaccination (P = 0.04).     

奉化市人群麻疹抗体水平监测及初中学生麻疹疫苗加强接种效果观察

目的分析奉化市1957-2006年麻疹流行病学特征,了解奉化市人群麻疹免疫水平及对初中学生加强接种麻疹疫苗后的免疫效果,为修定麻疹疫苗加强免疫方案提供客观依据。方法按照麻疹疫苗使用和计划免疫冷链装备情况将奉化市1957-2006年麻疹疫情划分为4个阶段进行比较;随机选取该市孕妇、婴幼儿、小学、初中、高中学生和育龄妇女共1500余人次进行麻疹IgG抗体监测,对2005年暴发过麻疹并进行过麻疹疫苗应急接种的西坞初中学生和2006年加强接种麻疹疫苗的莼湖初中学生进行免疫效果分析。麻疹IgG抗体检测采用ELISA定量法。结果4阶段麻疹年均发病率和年龄构成差异有统计学意义,发病年龄由幼儿和学龄前儿童为主,向8月龄以下小婴儿和15岁以上大年龄组人群转移;2005年该市本地人口8月龄以下小婴儿和15岁以上人群发病分别占25.86%和72.41%。6～8月龄婴儿麻疹IgG抗体GMC为51IU/L,8月龄婴儿麻疹疫苗初免成功率为100%,保护性抗体阳性率为94.12%,GMC为1352IU/L;18月复种后保护性抗体阳性率达100%,GMC为2333IU/L,小学高年级、初高中学生、育龄妇女及孕妇保护性抗体阳性率在46%～68%之间,GMC在783IU/L～901IU/L之间;西坞初中学生应急接种麻疹疫苗1年后保护性抗体阳性率为80.10%,GMC为1889IU/L,莼湖初中学生加强接种麻疹疫苗1月后保护性抗体阳性率为97.64%,GMC为2354IU/L。结论8月龄和18月龄麻疹疫苗初免和复种免疫效果良好,10岁以上人群麻疹IgG抗体水平下降,对初中学生进行麻疹疫苗加强接种免疫效果明显。建议调整现行麻疹的免疫策略,对初中学生进行麻疹疫苗加强接种,以削平大小两端年龄麻疹发病高峰,实现WHO西太区提出的到2012年消除麻疹的目标。