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 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.     

A school-based measles outbreak: the effect of a selective revaccination policy and risk factors for vaccine failure

Persons who received measles vaccine between 12 and 14 months of age have been found to be at increased risk of measles compared with those vaccinated at greater than or equal to 15 months of age. Because of this, in 1987 the Immunization Practices Advisory Committee of the US Public Health Service recommended that, during measles outbreaks, revaccination of persons vaccinated at 12-14 months of age be considered. During a school-based outbreak in New Mexico in 1987, the authors evaluated the effect of a mandatory revaccination policy in affected schools. Before the effect of revaccination, the overall attack rate in persons vaccinated at greater than or equal to 12 months of age was 4.1 cases/1,000 students; afterward, the risk was significantly reduced by 73%, to 1.1/1,000 students. The attack rate among students targeted for revaccination declined 100%, compared with 41% among those not revaccinated. Overall, attack rates were significantly lower in schools conducting revaccination early compared with schools holding later revaccination. In a retrospective cohort study of single-dose vaccines in one school, age at vaccination was not associated with risk of disease; however, persons vaccinated greater than or equal to 10 years before the outbreak were at increased risk, independently of age at vaccination. Revaccination of persons whose most recent vaccination was between 12 and 14 months of age appeared to control transmission in this outbreak. Further studies are needed to confirm these observations and to evaluate the effect of other revaccination efforts during outbreaks.     

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.     

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.     

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.     

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.     

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。     

Measles outbreaks in the Mozambican refugee camps in Malawi: the continued need for an effective vaccine

Between November 1988 and January 1989, measles outbreaks occurred in 11 Mozambican refugee camps in Malawi with five camps principally affected. A total of 1214 cases were reported. Despite the reduction of the age of measles vaccination to six months in 1987, attack rates were highest in children aged 6-9 months (10-26%); rates were also high in the 0-5 month age group (3-21%). The case-fatality rate was high among children less than five years old (15-21%). Children were being inappropriately vaccinated, either being vaccinated at less than six months of age (2-29%) or failing to receive a second dose if vaccinated at six months (0-25%). With vaccine coverage between 66-87%, vaccine efficacy in children less than five years old was estimated to be more than 90% in the camps principally affected. Reduction of the age of vaccination leads to logistical problems in vaccine delivery in refugee situations. These outbreaks again indicate the need to improve vaccine coverage with the existing Schwarz vaccine, and also highlight the urgent need for an effective single dose measles vaccine for children less than nine months of age.     

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.     

2010年台州市麻疹流行病学特征分析

目的 了解2010年浙江省台州市麻疹发病情况并分析其流行病学特征.方法 根据中国疾病监测信息报告管理系统的专病管理系统资料,对2010年台州市麻疹流行病学特征进行描述性分析.结果 2010年台州市确诊麻疹病例99例,主要发生在4～6月,年龄小于1周岁组为麻疹高发年龄组,占总病例数的33.33％,20～40岁年龄组存在发病小高峰.无免疫史者和免疫史不详者占76.76％.流动人口病例数占总病例数的23.23％,麻疹病例院感史例数占26.26％.结论 年龄小于1周岁婴儿为麻疹控制中的重点人群.应尽可能提高儿童麻疹疫苗接种的及时性,加大查漏补种工作的力度,提高外来流动儿童的免疫覆盖率,并加强疫情监测,预防控制麻疹暴发.     

Role of schools in the transmission of measles in rural Senegal: implications for measles control in developing countries

Patterns of measles transmission at school and at home were studied in 1995 in a rural area of Senegal with a high level of vaccination coverage. Among 209 case children with a median age of 8 years, there were no deaths, although the case fatality ratio has previously been 6-7% in this area. Forty percent of the case children had been vaccinated against measles; the proportion of vaccinated children was higher among secondary cases (47%) than among index cases (33%) (prevalence ratio = 1.36, 95% confidence interval (CI) 1.04-1.76). Vaccinated index cases may have been less infectious than unvaccinated index cases, since they produced fewer clinical cases among exposed children (relative risk = 0.55, 95% CI 0.29-1.04). The secondary attack rate was lower in the schools than in the homes (relative risk = 0.31, 95% CI 0.20-0.49). The school outbreaks were protracted, with 4-5 generations of cases being seen in the two larger schools. Vaccine efficacy was found to be 57% (95% CI -23 to 85) in the schools and 74% (95% CI 62-82) in the residential compounds. Measles infection resulted in a mean of 3.8 days of absenteeism per case, though this did not appear to have an impact on the children's grades. Among the index cases, 56% of children were probably infected by neighbors in the community, and 7% were probably infected at health centers, 13% outside the community, and 24% in one of the three schools which had outbreaks during the epidemic. However, most of the school-related cases occurred at the beginning and therefore contributed to the general propagation of the epidemic. To prevent school outbreaks, it may be necessary to require vaccination prior to school entry and to revaccinate children in individual schools upon detection of cases of measles. Multidose measles vaccination schedules will be necessary to control measles in developing countries.     

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.     

Measles epidemic in Romania, 1996-1998: assessment of vaccine effectiveness by case-control and cohort studies

A measles epidemic occurred in Romania with 32,915 cases and 21 deaths reported between November 1996 and June 1998, despite high vaccination coverage since the early 1980s. Most cases were unvaccinated children aged <2 years and vaccinated school-aged children. A case-control study among preschool children and a cohort study among primary-school children were conducted to estimate effectiveness of Romanian-produced measles vaccine, and to evaluate age at vaccination and waning immunity as risk factors for vaccine failure. Both studies indicated that measles vaccine was highly effective. One dose reduced the risk for measles by 89% (95% confidence interval (CI) 85, 91); two doses reduced the risk by 96% (95% CI 92, 98). Children vaccinated at <1 year of age were not at increased risk for measles compared with children vaccinated at > or =1 year. Waning immunity was not identified as a risk factor since vaccine effectiveness was similar for children vaccinated 6-8, 9-11, and 12-14 years in the past. Because specific groups were not at risk for vaccine failure, an immunization campaign that targets all school-aged children who lack two doses may be an effective strategy for preventing outbreaks. A mass campaign followed by increased first-dose coverage should provide the population immunity required to interrupt indigenous measles virus transmission in Romania.     

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 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.     

Risk of pregnancy among adolescent schoolgirls participating in a measles mass immunization program

A large measles vaccination program in the Albuquerque, New Mexico public schools in 1981, conducted according to US Public Health Service guidelines, was studied to determine rates of pregnancy among adolescent vaccinees. Pre-vaccination counseling of 1,922 clinic attendees prevented seven pregnant girls from being vaccinated. Despite counseling, of 1,913 female vaccinees age 13-18 years old, two were pregnant at the time of vaccination (1.05 pregnancies per 1,000 vaccinees) and an additional four girls became pregnant in the three months after vaccination (2.1 pregnancies per 1,000 vaccinees). Data supporting low or absent fetal risks from measles and rubella vaccine, combined with the low pregnancy rate among vaccinees documented in this study, support the reasonableness of the recommended strategy for measles and rubella vaccination of secondary schoolgirls.     

重庆市南岸区2004-2008年麻疹疫情流行病学分析和控制对策

目的分析麻疹流行的特征和分布规律,为进一步控制和消除麻疹提供科学依据。方法对2004-2008年麻疹监测资料进行描述性流行病学分析。结果 2004-2008年共报告506例麻疹病人,局部散在发病,全区各个乡镇和街道均有病例发生,病例分布存在明显的地区差异,病例发病集中在4~8月份;人群以散居儿童、学生和托幼儿童为主,占80.43%;发病年龄主要集中在5岁以下,占总发病人数的69.56%;未达麻疹疫苗初免接种年龄(8月龄)中的人群发病占总发病数的20.29%,已达初免年龄的发病人群中无免疫接种史者达35.20%。结论南岸区麻疹近年来总发病率有所上升,主要是散在发病,需要进一步采取针对性有效措施,以达到有效控制和消除麻疹的目标。     

Measles control efforts in urban Africa complicated by high incidence of measles in the first year of life

A measles vaccination coverage of between 50 and 60% has been achieved in Kinshasa, Zaire, from 1980-1985. During that interval, the annual number of measles cases and the incidence rate of measles reported by a surveillance system remained similar, and measles epidemics occurred in alternating years. The estimated number of measles cases in Kinshasa is 87,600 per year. Of reported measles cases, 27% occurred in children under nine months of age, younger than the recommended age at vaccination. Two results expected in a partially vaccinated population, a reduction in measles incidence greater than the level of vaccination coverage and a shift in the age distribution of measles to older children, have not been observed. Measles control in Kinshasa will require a vaccination coverage of higher than 60%. In addition, given the age-specific risk of measles infection here, a measles vaccine that would be effective when given before nine months of age would be an important element in controlling measles transmission. Because the epidemiology of measles in Kinshasa is a likely consequence of its urban environment, such a vaccine would represent a significant advance toward the control of measles in urban Africa.     

Control of a measles outbreak in an elementary school. Baltimore County,Md. 1975.

Between April 18 and May 20, 1975, 16 cases of measles occurred in pupils in an elementary school in Baltimore County, Md., and 1 case occurred in a sibling at a junior high school. Measles was serologically confirmed in 16 of these pupils. Attack rates were determined by grade and by vaccine status. The measles attack rate was 2.1 percent for the 377 children who had been given measles vaccine at 1 year of age or later. The rates were 27.8 percent (13 times higher) for those vaccinated at less than 10 months of age and 20.0 percent (10 times higher) for those with no definite history of vaccine. The higher attack rates for children who were vaccinated only before 10 months of age supports the 1972 recommendation of the Public Health Service Advisory Committee on Immunization Practices that children vaccinated before this age need to be revaccinated with live measles virus vaccine to assure full protection. The finding that 2 of 10 children with a history of measles became ill during the outbreak suggests that such histories are not a totally reliable indicator of immunity. Containment of the outbreak was attributed to the high level of immunity in the community and prompt initiation of control measures.