Seroepidemiology and evaluation of passive surveillance during 1988-1989 measles outbreak in Taiwan

Effect of early measles vaccination on long-term protection: A systematic review

BACKGROUND

In North America, the first dose of a measles-containing vaccine (MCV1) is administered at ≥12 months of age. However, MCV1 may be given to infants <12 months living in highly endemic areas or traveling to these areas. Although an early dose of MCV1 leads to immediate protection, it remains unclear how this impacts long-term immunity.

METHODS

This systematic review and meta-analysis evaluates the impact of MCV1 given at <12 months vs. ≥12 months of age on long-term immunogenicity and vaccine effectiveness, with long-term defined as at least one-year post-vaccination. PubMed, EMBASE, Global Health, Web of Science and Scopus were searched on October 31st, 2019. Studies were included if they included a cohort of infants vaccinated <12 months of age and evaluated long-term immunogenicity, vaccine efficacy, or effectiveness.

RESULTS

A total of 51 texts were identified: 23 reported outcomes related to vaccine effectiveness and 30 to immunogenicity. Infants vaccinated with MCV1 < 12 months of age showed an overall higher risk of measles compared to ≥12 months of age (RR = 3.16, 95% CI: 2.00, 5.01; OR = 2.46, 95% CI: 1.40, 4.32). Risk of measles decreased with increasing age at first vaccination, with those vaccinated with one dose ≥15 months at a lesser risk compared to 12-14 months or <12 months. Measles seroconversion and seropositivity was not affected by age at first vaccination, but antibody levels were significantly lower in the MCV1 < 12-month group (MD = -0.40, 95% CI: -0.71, -0.09).

CONCLUSION

Long-term measles seroconversion and seropositivity did not appear to be affected by age at MCV1, while vaccine effectiveness decreased with younger age. There was not enough evidence to look at the effect of age at MCV1 on immune blunting.

Effect of age at vaccination on the measles vaccine effectiveness and immunogenicity: systematic review and meta-analysis

Background

The objectives of this review were to evaluate the effect of age at administration of the first dose of a measles-containing vaccine (MCV1) on protection against measles and on antibody response after one- and two-dose measles vaccinations.

Methods

We conducted a systematic review of the PubMed/MEDLINE, Embase, Web of Science and Cochrane databases (1964–2017) to identify observational studies estimating vaccine effectiveness and/or measles attack rates by age at first vaccination as well as experimental studies comparing seroconversion by age at first vaccination. Random effect models were used to pool measles risk ratios (RR), measles odds ratios (OR) and seroconversion RR of MCV1 administered at < 9, 9–11 or ≥ 15 months compared with 12 or 12–14 months of age.

Results

We included 41 and 67 studies in the measles protection and immunogenicity analyses. Older age at MCV1, from 6 to ≥15 months, improved antibody response and measles protection among one-dose recipients. Pooled measles RR ranged from 3.56 (95%CI: 1.28, 9.88) for MCV1 at < 9 months to 0.48 (95%CI: 0.36, 0.63) for MCV1 at ≥15 months, both compared to 12–14 months. Pooled seroconversion RR ranged from 0.93 (95%CI: 0.90, 0.96) for MCV1 at 9–11 months to 1.03 (95%CI: 1.00, 1.06) for MCV1 at ≥15 months, both compared to 12 months. After a second dose, serological studies reported high seropositivity regardless of age at administration of MCV1 while epidemiological data based on few studies suggested lower protection with earlier age at MCV1.

Conclusions

Earlier age at MCV1 decreases measles protection and immunogenicity after one dose and might still have an impact on vaccine failures after two doses of measles vaccine. While two-dose vaccination coverage is most critical to interrupt measles transmission, older age at first vaccination may be necessary to keep the high level of population immunity needed to maintain it.

Seroepidemiology for measles among elementary school children in Northern Taiwan

BACKGROUND

Despite the high vaccination coverage in Taiwan, sporadic cases or small cluster of measles still occur every year. Nevertheless, few studies provided information about the serostatus for measles in recent years. This cross-sectional survey aimed to establish the seroepidemiologic data of measles among elementary school children in New Taipei City, Taiwan during 2012-2013.

METHODS

A multistage stratified sampling design using 14 variables was employed to obtain samples. All selected schoolchildren were bled for the serologic tests of measles by both chemiluminescence immunoassay (CLIA) and enzyme immunoassay (EIA).

RESULTS

A total of 856 schoolchildren from 14 schools were recruited in this study. Among these individuals, the overall seropositive rates for measles were 82.24% and 92.17% by the Liaison and NovaLisa assays, respectively. For schoolchildren in each grade, the seropositive rates were > 90% for Grade 1, and then decreased gradually to 70-80% for Grade 6 (p < 0.001 for both methods). A decay of measles-specific immunoglobulin G titers was also observed with the maximum drop between Grade 1 and Grade 2 (declining trend of p < 0.001 for both).

CONCLUSION

Although the seropositive rate of measles was > 90% for Grade 1, the rate for Grade 6 was only in the range of 70-80%, which may be a challenge to prevent outbreaks of measles in the future and should be monitored meticulously.

Seroepidemiology: an underused tool for designing and monitoring vaccination programmes in low- and middle-income countries

Seroepidemiology, the use of data on the prevalence of bio-markers of infection or vaccination, is a potentially powerful tool to understand the epidemiology of infection before vaccination and to monitor the effectiveness of vaccination programmes. Global and national burden of disease estimates for hepatitis B and rubella are based almost exclusively on serological data. Seroepidemiology has helped in the design of measles, poliomyelitis and rubella elimination programmes, by informing estimates of the required population immunity thresholds for elimination. It contributes to monitoring of these programmes by identifying population immunity gaps and evaluating the effectiveness of vaccination campaigns. Seroepidemiological data have also helped to identify contributing factors to resurgences of diphtheria, Haemophilus Influenzae type B and pertussis. When there is no confounding by antibodies induced by natural infection (as is the case for tetanus and hepatitis B vaccines), seroprevalence data provide a composite picture of vaccination coverage and effectiveness, although they cannot reliably indicate the number of doses of vaccine received. Despite these potential uses, technological, time and cost constraints have limited the widespread application of this tool in low-income countries. The use of venous blood samples makes it difficult to obtain high participation rates in surveys, but the performance of assays based on less invasive samples such as dried blood spots or oral fluid has varied greatly. Waning antibody levels after vaccination may mean that seroprevalence underestimates immunity. This, together with variation in assay sensitivity and specificity and the common need to take account of antibody induced by natural infection, means that relatively sophisticated statistical analysis of data is required. Nonetheless, advances in assays on minimally invasive samples may enhance the feasibility of including serology in large survey programmes in low-income countries. In this paper, we review the potential uses of seroepidemiology to improve vaccination policymaking and programme monitoring and discuss what is needed to broaden the use of this tool in low- and middle-income countries.

Changes in measles seroepidemiology of healthcare workers in southern Taiwan

To assess the measles seroepidemiology of healthcare workers (HCWs), from 2004 to 2009 all newly recruited staff at a university hospital in Taiwan, were tested for specific immunoglobulin G antibodies for measles virus using enzyme-linked immunosorbent assays. A total of 1584 HCWs were included. The positivity rate of measles antibody for physicians and nurses was about 90%. The positivity of measles antibody in different age groups was 78·1%, 93·9% and 94·2% for 20-29, 30-39 and ≥40 years age groups, respectively. Equivocal results were more frequent in the 20-29 (17·1%) years age group. A lack of antibody against measles was reported for 66 (4·2%) of those tested. Medical student (8·3%) and housekeeping personnel (5·3%) had the greatest lack of antibodies. This study demonstrates the waning measles immunity in younger HCWs in Taiwan, which poses the potential risk of nosocomial transmission of measles. Periodic surveillance and revaccination of susceptible HCWs is recommended.

Absence of endemic measles transmission in a highly vaccinated population from 1999 to 2008: implications of sustained measles elimination in Taiwan

BACKGROUND

Measles remains a leading vaccine-preventable cause of child mortality worldwide. The impact of vaccination programs can be seen in the increasingly low incidence of measles. However, cases of measles continue to occur in low numbers every year in Taiwan. We assessed the epidemiology of measles in Taiwan from 1999 to 2008 with a focus on domestic versus imported cases.

METHODS

We analyzed the data reported to surveillance systems at the Taiwan Center for Disease Control, where viral isolation was performed.

RESULTS

A total of 84 measles cases were reported from 1999 to 2008 in Taiwan with the incidence of measles varying from 0 to 1.5 per 1,000,000 people per year, peaking in 2002 and again in 2008. The incidence decreased with increasing age in both males and females. Among the 84 reported measles cases, 39 (46%) originated internationally, 8 (10%) were epidemiologically linked to imported cases and the source was unknown in 37 (44%) of the cases. The unknown-source cases were analyzed for potential evidence of endemic measles transmission. Most of the measles cases that occurred in Taiwan from 1999 to 2008 were associated with imported cases. No endemic transmission of measles in Taiwan was identified.

CONCLUSIONS

This study suggests that maintaining the high rate of vaccination coverage is needed to prevent future outbreak and sustain the elimination of measles in Taiwan.

Molecular evolution of measles viruses circulated in Taiwan 1992-2008

Genetic analyses of viral samples from 74 laboratory confirmed measles cases occurring in Taiwan during 1992-2008 identified six viral genotypes D3, D5, D9, G2, H1 and H2. The most frequently detected genotype, H1, was associated with outbreaks in 1994 and 2002, and was the likely indigenous genotype in 1992. In response to the outbreaks, two catch-up campaigns were launched and a routine second dose of measles, mumps, and rubella vaccine at entry to elementary school was introduced. The vaccination campaigns successfully reduced the number of measles cases in Taiwan, and many of the more recent cases can be traced to importations, primarily from other Asian countries. A number of measles genotypes which were associated with outbreaks in other Asian countries were detected among the more recent cases. The more recent genotype H1 viruses had sequences that were identical to those currently circulating in China or associated with international importation of virus.

Modelling respiratory infection control measure effects

One of the most pressing issues in facing emerging and re-emerging respiratory infections is how to bring them under control with current public health measures. Approaches such as the Wells-Riley equation, competing-risks model, and Von Foerster equation are used to prioritize control-measure efforts. Here we formulate how to integrate those three different types of functional relationship to construct easy-to-use and easy-to-interpret critical-control lines that help determine optimally the intervention strategies for containing airborne infections. We show that a combination of assigned effective public health interventions and enhanced engineering control measures would have a high probability for containing airborne infection. We suggest that integrated analysis to enhance modelling the impact of potential control measures against airborne infections presents an opportunity to assess risks and benefits. We demonstrate the approach with examples of optimal control measures to prioritize respiratory infections of severe acute respiratory syndrome (SARS), influenza, measles, and chickenpox.

Modelling vaccination programmes against measles in Taiwan

Vaccination has proved a powerful defence against measles. We reappraise measles seroepidemiological data in Taiwan from 1974 to 2004 having robust age-stratified serological information on exposure and immunity to quantitatively characterize measles vaccination programmes. We dynamically model measles seroepidemiology to estimate age-dependent intensity of infection associated with the effects of different contact patterns on pre- and post-vaccination. The WAIFM (who acquires infection from whom) contact matrix is employed to describe the transmission between and within each age group. A deterministic SEIR (susceptible-exposed-infected-recovery) model is used to capture subpopulation dynamics. Our study shows that mass regional or nationwide vaccination programmes could greatly reduce the potential for a major measles epidemic and have strong direct effects on the potential impact of childhood vaccination. We parameterize a predictive model that should reduce the socio-economic costs of measles surveillance in Taiwan and thereby encourage its continuance, especially for preschool children.

Assessment of routine surveillance data as a tool to investigate measles outbreaks in Mozambique

BACKGROUND

Measles remains a major public health problem in Mozambique despite significant efforts to control the disease. Currently, health authorities base their outbreak control on data from the routine surveillance system while vaccine coverage and efficacy are calculated based on mathematical projections of the target population. The aim of this work was to assess the quality of the measles reporting system during two outbreaks that occurred in Maputo City (1998) and in Manica Province (2002).

METHODS

Retrospectively, we collected data from the routine surveillance system, i.e. register books at health facilities and weekly provincial and national epidemiological reports. To test whether the provinces registered an outbreak, the distribution of measles cases was compared to an endemic level established based on cases reported in previous years.

RESULTS

There was a significant under-notification of measles cases from the health facilities to the province and national level. Register books, the primary sources of information for the measles surveillance system, were found to be incomplete for two main variables: "age" and "vaccination status".

CONCLUSION

The Mozambican surveillance system is based on poor quality records, receives the notification of only a fraction of the total number of measles in the country and may result in failures do detect epidemics. The measles reporting system does not provide the data needed by Expanded Program on Immunisation managers to make evidence-based decisions, nor does it allow in-depth analysis to monitor measles epidemiology in the country. The progress of Mozambique to the next stage of measles elimination will require an improvement of the routine surveillance system and a stronger Health Information System.

[Contribution of unvaccinated siblings to a measles outbreak in Switzerland]

BACKGROUND

A measles outbreak occurred in Geneva between March and July 2003. An investigation was conducted to determine its magnitude, identify predominant modes of transmission, and assess disease outcome.

METHODS

In Switzerland, measles notification has been mandatory for physicians since 1999 and laboratories since 1988. All cases were investigated and followed up by interviewing physicians using a standardized questionnaire. Viral genotype was determined for 4 cases using a saliva specimen processed at the Robert Koch Institute, Berlin. Geographic distribution of cases and vaccination coverage were compared.

RESULTS

Overall, 54 cases were notified. Fifty-three cases were between 10 and 19 years of age. Ninety-four percent (n = 46) of 49 cases with known vaccination status were not vaccinated and none were fully immunized (2 doses). Measles complications occurred among 19% (n = 7) of the 36 patients with follow up information: pneumonia (n = 4, combined with pericarditis and hepatitis in one case) and bronchitis (n = 3). Three persons were hospitalized. No complication was reported among 3 persons partially vaccinated (1 dose). The virus belonged to genotypes D8 and D5. Five separate clusters of related cases included 74% of all cases. Transmission mainly occurred within families (43% of all cases) and school (28%). Two of the most affected areas had measles vaccination coverage well below the cantonal average.

CONCLUSION

Low vaccination coverage combined with clusters of unvaccinated household contributed to continued virus circulation and represents a threat to the canton of Geneva as new outbreaks of measles may reoccur.

Seroprevalence of neutralizing antibodies to measles virus in a vaccinated population in Iran, 1998

Measles is an acute highly infectious viral disease. Although live attenuated vaccine is used throughout the world, outbreaks of disease still occur in many countries including Iran. In this cross-sectional study, by implementing a viral neutralization test and cell culture techniques, the seroprevalence of neutralizing anti-measles antibodies was assessed. Three hundred and fifty-four blood samples were collected and random-cluster classified from healthy subjects 6 months to 16 years old, residing in the town of Khodabandeh and its rural areas. Of the total subjects, 174 (49.2%) were girls and 180 (50.8%) were boys. From 354 subjects studied, 310 (87.6%) had neutralizing anti-measles antibody titer of 1:8 or higher and were considered to be immune and 44 (12.4%) had lower antibody titers. At the time of specimen collection, information with regards to age, sex, history of vaccination and place of residence were collected. Chi2 statistical test demonstrated a significant association between immune status and grouped age at the time of first vaccination (p < 0.009). The proportion test indicated significant differences in rate of seropositivity in paired age groups (3-8 vs. 9-11 and 9-11 vs. 12-64 months) (p < 0.02). The use of reliable techniques for assessing success of vaccination programs and performing seroepidemiological studies in order to organize national programs of control and eradication of measles are necessary.

Multiplexed immunoassays by flow cytometry for diagnosis and surveillance of infectious diseases in resource-poor settings

An accurate, rapid and cost-effective diagnosis is the cornerstone of efficient clinical and epidemiological management of infections. Here we discuss the relevance of an emerging technology, multiplexed immunoassays read by flow cytometry, for the diagnosis of infectious diseases. In these assays, multiple fluorescent microspheres, conjugated to different antigens or antibodies, constitute the solid phase for detecting antibodies or antigens in biological samples. These assays seem to be more sensitive than traditional immunoassays, have a high throughput capacity, and provide a wide analytical dynamic range. Additionally, they have multiplexing ability-ie, they are capable of measuring multiple antibodies or antigens simultaneously. We discuss four different areas where this technology could make an impact in resource-poor settings: (i) infections causing rash and fever in children; (ii) sero-epidemiological studies on vaccine-preventable diseases; (iii) management of genital ulcers and vaginal discharge; and (iv) screening of infections in blood banking. We predict a widespread use for a new breed of small, affordable, practical flow cytometers as field instruments for replacing ELISA and RIA tests, which will also be capable of doing cellular immunological tests such as CD4+ T-cell enumeration and Plasmodium falciparum detection in whole blood.

Measles IgG seroprevalence prior to mass vaccination in Taiwan

OBJECTIVES

Measles vaccine was licensed for use in Taiwan in 1968 and mass vaccination has been implemented since 1978. Serological surveys were conducted to characterize measles seroepidemiology prior to mass vaccination.

METHODS

Measles IgG was quantitatively measured in 1564 serum samples collected from four populations (nationwide, urban, rural, and mountain areas) during 1974-80 with a commercial EIA kit. The nationwide samples covered age groups from 3 months to 19 years, but the other three samples only covered school-aged children. The cut-off value of seropositivity was set at 100 mIU/ml.

RESULTS

In the nationwide samples, measles IgG seroprevalence decreased from 50% at 3-5 months to 13% at 6-11 months, then increased rapidly to 55% at 1-1.9 years and reached 98% at 7-7.9 years of age; this was maintained to young adulthood. In all four samples, seroprevalence also reached >97% in individuals >10 years of age. Semiquantitative analysis found that 24%(10/42) of 1-1.9-year-old children but only 4%(1/24) of 15-19-year-old adolescents had low level measles IgG (100-399 mIU/ml). In addition, the distribution of measles IgG level in 1-1.9-year-old children had two peaks at 200-399 and 1600-3199 mIU/ml, whereas only one peak at 1600-3199 mIU/ml had been found in 15-19-year-old adolescents. The median age of measles infection (i.e. 50% seroprevalence) in Taiwan was 1.4 and 2.1 years, respectively, before and after excluding individuals with measles IgG 100-399 mIU/ml that may have resulted from vaccination.

CONCLUSIONS

Measles seroepidemiology in Taiwan in the 1970s seemed to be more similar to that in a developing country rather than in an industrialized country, and there was a low median age of infection.

Measles seroepidemiology and decay rate of vaccine-induced measles IgG titers in Taiwan, 1995-1997

Community-based seroepidemiologic studies were conducted to monitor the effectiveness of measles immunization programmes and to estimate the decay rate of vaccine-induced measles IgG titres. Sera collected from a mountain (792 sera), rural (875 sera) and urban (894 sera) populations in 1995-1997 were available. Measles IgG was quantified using a commercial EIA kit. Measles IgG seroprevalence and geometric mean titre (GMT) were calculated by setting the cut-off titre at 50 mIU/ml. The decay rate of measles IgG titres was estimated by assuming that the measles IgG titres, without exposing to wild measles virus, decay exponentially and constantly after 1 year post vaccination. The half-life of measles IgG titres was calculated from the corresponding decay rate. Measles IgG seroprevalences in these three populations have reached >95% in school children (7-18 years old) and >98% in young adults (19-25 years old) but varied from 87 to 96% in pre-school children (4-6 years old). Two-dose vaccinees, comparing with 1-dose vaccinees, had a significantly higher seroprevalence (98 versus 92%, P<0.01) and a slightly longer half-life of measles IgG titres (61 versus 27 months, P=0.08) but the measles IgG GMT in the two groups did not differ significantly (675 versus 618 mIU/ml, P=0.78).

Protective titres of measles neutralising antibody

A nation-wide measles outbreak occurred in 1988 in Taiwan. A retrospective cohort study was conducted to define the protective titre of measles neutralising (NT) antibody. Paired sera collected in 1987 and 1988 were available from 190 individuals born in 1984 who had participated in an annual hepatitis B immunisation follow-up from 1986 to 1991. Measles NT titres were quantified using a standardised neutralisation enzyme immunoassay. Measles infection was defined as a >/=4-fold rise in NT titre or seroconversion between paired sera. Symptomatic measles infection was ascribed to individuals who had measles infection and who reported measles-like symptoms between 1987 and 1988. Results demonstrated a dose-response relationship between pre-exposure NT titres and protection against measles infection. 47 of 48 individuals with measles infection in 1988 had pre-exposure NT titres </=1,017 mIU/ml; all 12 symptomatic cases had pre-exposure NT titres </=434 mIU/ml. Eleven vaccinees had pre-exposure NT titres <50 mIU/ml, of whom nine developed asymptomatic infection. The study suggests that measles NT titres >1, 000 mIU/ml may prevent measles infection and NT titres >500 mIU/ml may prevent symptomatic infection but vaccinees with undetectable or low NT titres may not necessarily be susceptible to symptomatic infection.

Post mass-immunization measles outbreak in Taoyuan County, Taiwan: dynamics of transmission, vaccine effectiveness, and herd immunity

OBJECTIVES

Analysis of national surveillance data and a seroepidemiologic investigation were conducted to elucidate the causes and epidemiologic characteristics of a measles outbreak in Taoyuan, Taiwan, 1994.

METHODS

Measles cases were identified through a national surveillance system. Reported cases and their physician or school nurses were interviewed to trace additional suspect cases and were sampled for serologic diagnosis. Measles-specific IgG and IgM were assayed. A confirmed case was defined as being positive for measles IgM test but not having received measles vaccination within the previous 3 months.

RESULTS

The outbreak began in Taoyuan City in December 1993 and continued to spread in primary schools and kindergartens, but caused only sporadic cases in neighboring towns. Among 42 confirmed cases, 15 (38%) were primary school children and 16 (38%) were kindergarten children. Among 24 confirmed cases with a vaccination record, 7 had one dose of vaccination, 4 had two doses of vaccination, and 13 (54%) were unvaccinated. The overall measles susceptible proportion at a kindergarten before the outbreak was 8.1% (17/209) and the overall measles cumulative incidence among susceptibles was 0.65 (11/17).

CONCLUSIONS

A measles vaccination coverage of 82% with the first dose at 9 months of age and 63% with the second dose (measles, mumps, and rubella) at 15 months was inadequate to block measles virus circulation in Taoyuan City in 1994. The city center, with a growing population, represents a high risk as an epicenter for measles outbreaks. Measles outbreaks may occur in a school population with 92% herd immunity.

[Measles outbreaks: considerations apropos of the outbreaks investigated in Catalonia (1990-1995)]

OBJECTIVES

To determine the factors associated with outbreak size in Catalonia.

METHODS

Outbreaks over the period 1990-95 were investigated. A comparison was run between outbreaks of more than 6 cases with respect to outbreaks of 2-6 cases in function of the following variables: median age of cases, transmission setting and year of presentation. Multiple logistic regression was used to asses the independent effect of each variable, with the adjusted odds ratio (ORa) and their 95% confidence interval (CI) being obtained.

RESULTS

In all, 45 outbreaks were studied, with 595 cases of measles 39.5% of outbreaks occurred in the 6-10 age group. Outbreaks of more than 6 cases had a higher likelihood of appearing in a school setting (ORa = 4.3, CI 95% 1.0-17.6); but there were no association with age (ORa = 2.1, CI 95% 0.5-9.2) or occurring prior to 1994 (ORa = 0.9, CI 95% 0.2-3.6).

CONCLUSIONS

School setting determines the outbreak size of measles and demands to apply specific preventive strategies.

Secondary failure rates of measles vaccines: a metaanalysis of published studies

BACKGROUND

Recent measles outbreaks in highly vaccinated populations have highlighted the role of vaccine failure as a barrier to the elimination of measles. We sought to estimate the rate of secondary failure (clinical measles after vaccine-induced seroconversion) of measles vaccines using metaanalysis.

METHODS

We identified 1411 studies of which 125 were relevant. From these we found 10 original studies of healthy subjects with sufficient details to calculate a pooled secondary failure rate. We performed a test for homogeneity before any pooling.

RESULTS

Although significant heterogeneity prevented their pooling as a single group, the studies fell into three homogeneous groups suitable for pooling. Group A studies used killed vaccine whereas the other two groups (Groups B and C) of studies used live vaccine. These latter groups differ in that the studies in Group B share higher failure rates and are difficult to interpret with respect to the lack of verification of vaccination, immunization before 12 months of age and a non-North American study site and vaccine manufacturer. Those studies in Group C, in which US subjects were older than 12 months at vaccination and received a live US-manufactured vaccine that was documented in a medical record, had a failure rate of 0 of 2031 with a 95% confidence interval of 0.0 to 0.147%.

CONCLUSIONS

Although reports of measles related to secondary failure exist, studies that permit the calculation of the rate of secondary failure demonstrate that the rate appears to be < 0.2%.

Epidemiology of measles in Taiwan: dynamics of transmission and timeliness of reporting during an epidemic in 1988-9

We analysed nation-wide reported measles cases during the 1988-9 epidemic and found that longer duration and wider spread were two major characteristics of the outbreak. All the 22 county/city index cases were reported with a delay of > 4 days and 64% were aged 5-14 years. This epidemic occurred mainly among 5-14-year-old school-children (59%), infants under 1 year (19%), and pre-school children (18%). The overall attack rate was 0.63 cases per 10,000 population, with the highest attack rate (7.4 cases per 10,000 population) occurring in infants. Among 280 confirmed cases < 15 months of age, 9-month-old infants (42 cases) had a higher risk of measles and peaked at 10 months (49 cases). This epidemic started in March 1988 among 5-9-year-old children in the northern suburban area, then spread to Taipei City and neighbouring counties or cities. It continued to spread from the northern to southern and western areas during the summer vacation and New Year holidays. Multiple logistic regression analysis showed that the delay of measles reporting was strongly associated with the cases infected early in the epidemic (OR = 6.9, P < 0.001) and reported from teaching hospitals (OR = 2.6, P < 0.001). The reappearance of high attack rates among 5-9-year-old children in the 1985 and 1988-9 measles epidemics in Taiwan indicated the persistence of pockets of susceptible individuals even after mass immunization.