Nonclassic measles infections in an immune population exposed to measles during a college bus trip

Assessment of SARS-CoV-2 airborne infection transmission risk in public buses

Public transport environments are thought to play a key role in the spread of SARS-CoV-2 worldwide. Indeed, high crowding indexes (i.e. high numbers of people relative to the vehicle size), inadequate clean air supply, and frequent extended exposure durations make transport environments potential hotspots for transmission of respiratory infections. During the COVID-19 pandemic, generic mitigation measures (e.g. physical distancing) have been applied without also considering the airborne transmission route. This is due to the lack of quantified data about airborne contagion risk in transport environments.

In this study, we apply a novel combination of close proximity and room-scale risk assessment approaches for people sharing public transport environments to predict their contagion risk due to SARS-CoV-2 respiratory infection. In particular, the individual infection risk of susceptible subjects and the transmissibility of SARS-CoV-2 (expressed through the reproduction number) are evaluated for two types of buses, differing in terms of exposure time and crowding index: urban and long-distance buses. Infection risk and reproduction number are calculated for different scenarios as a function of the ventilation rates (both measured and estimated according to standards), crowding indexes, and travel times. The results show that for urban buses, the close proximity contribution significantly affects the maximum occupancy to maintain a reproductive number of <1. In particular, full occupancy of the bus would be permitted only for an infected subject breathing, whereas for an infected subject speaking, masking would be required. For long-distance buses, full occupancy of the bus can be maintained only if specific mitigation solutions are simultaneously applied. For example, for an infected person speaking for 1 h, appropriate filtration of the recirculated air and simultaneous use of FFP2 masks would permit full occupancy of the bus for a period of almost 8 h. Otherwise, a high percentage of immunized persons (>80%) would be needed.

Breakthrough Infections: A Challenge towards Measles Elimination?

Measles is one of the most contagious diseases known to man. Despite the existence of a safe and effective live attenuated vaccine, measles can appear in vaccinated individuals. Paradoxically, breakthrough cases increase as vaccination coverage in the general population rises. In measles endemic areas, breakthrough cases represent less than 10% of total infections, while in areas with high vaccination coverage these are over 10% of the total. Two different vaccination failures have been described: primary vaccination failure, which consists in the complete absence of humoral response and occurs in around 5% of vaccinated individuals; and secondary vaccination failure is due to waning immunity or incomplete immunity and occurs in 2–10% of vaccinees. Vaccination failures are generally associated with lower viral loads and milder disease (modified measles) since vaccination limits the risk of complicated disease. Vaccination failure seems to occur between six and twenty-six years after the last vaccine dose administration. This review summarizes the literature about clinical, serological, epidemiological, and molecular characteristics of measles breakthrough cases and their contribution to virus transmission. In view of the measles elimination goal, the assessment of the potential decline in antibody protection and the targeted implementation of catch-up vaccination are essential.

Waning immunity and re-emergence of measles and mumps in the vaccine era

Vaccine-preventable diseases (VPD) including measles and mumps have been re-emerging in countries with sustained high vaccine coverage. For mumps, waning immunity has been recognized as a major contributor to recent outbreaks. Although unvaccinated individuals account for most cases in recent measles outbreaks, the role of immune waning remains unclear. Accumulating serological and epidemiological evidence suggests that natural immunity induced by infection may be more durable compared to vaccine-induced immunity. As the proportion of population immunity via vaccination gradually increases and boosting through natural exposures becomes rare, risk of outbreaks may increase. Mechanistic insights into the coupled immuno-epidemiological dynamics of waning and boosting will be important to understand optimal vaccination strategies to combat VPD re-emergence and achieve eradication.

High ratio of measles-specific IgG/IgM associated with nodular pneumonia in vaccinated individuals

BACKGROUND

Vaccinated individuals infected with measles can develop nodular pneumonia. These cases can be misdiagnosed due to the absence of specific IgM and typical symptoms. An effective diagnostic tool is needed.

METHODS

During March 2016, adult inpatients in Yucheng People's Hospital were enrolled prospectively and included in the study. Patients were included if samples were obtained ≤14 days from the onset of fever. Measles virus was detected by RT-PCR of the oropharyngeal swab sample. Chest computed tomography scans and medical records were obtained. Oropharyngeal swabs and blood samples were collected for IgM and IgG testing, RT-PCR, and gene sequencing.

RESULTS

Sixteen patients were enrolled. Ten were found to have nodular pneumonia and were defined as the nodular group. The remaining six patients were defined as the control group. Measles-specific IgG titers in the nodular group were high (3618.3-5000mIU/ml), while IgM titers were low (<25mIU/ml); IgG titers in the control group were low (241.4-2560.3mIU/ml), while IgM titers were high (137-5000mIU/ml). No obvious viral mutation was detected in the nodular group.

CONCLUSIONS

Measles-associated nodular pneumonia was only evident in those patients with an IgG/IgM ratio >20. In measles outbreaks, the IgG/IgM ratio may be useful to identify nodular pneumonia.

A risk stratification approach to assessing for true cases of measles in a highly vaccinated population

OBJECTIVE

In Australia, the notification rate for measles fluctuates greatly between baseline and outbreak periods. We aimed to identify characteristics of notified cases that allow risk stratification in order to improve the efficiency of the public health response in an outbreak setting.

METHODS

Retrospective descriptive case series for all measles notifications made to the Victorian Government Department of Health between 1 August and 30 September 2013.

RESULTS

A total of 151 notifications were included in the analyses, of which 17 (11%) were confirmed as measles. Applying the clinical criteria of the measles case definition or identifying susceptible cases (determined by vaccination status) correctly identified all measles cases. Requiring cases to meet both criteria reduced sensitivity to 88%, but improved the positive predictive value (48% vs 25%) and retained a high negative predictive value (98.33%). Application of a risk stratification approach based on these features would have saved intensive public health follow-up for 79.5% of notifications in this outbreak.

CONCLUSIONS

Immune status and clinical features can reliably be used to predict which notifications are unlikely to become confirmed cases.

IMPLICATIONS

Risk stratification and modification of current surveillance practices may provide for a more efficient public health response, particularly during periods of increased case notification.

What assay is optimal for the diagnosis of measles virus infection? An evaluation of the performance of a measles virus real-time reverse transcriptase PCR using the Cepheid SmartCycler(®) and antigen detection by immunofluorescence

BACKGROUND

Despite the World Health Organization (WHO)-reported elimination of measles in Australia, importation of cases especially in travellers from Asia continues in Sydney, Australia's largest city. Laboratory confirmation supports clinico-epidemiological evidence of measles virus infection, and is needed to establish elimination.

OBJECTIVES

To evaluate the performance of a random access real-time reverse transcriptase polymerase chain reaction (RT-PCR) assay using the moderate complexity SmartCycler(®) platform, and measles antigen detection by immunofluorescence (IFA), for the detection of measles virus in patient samples.

STUDY DESIGN

One hundred samples comprising nose and throat swabs, nasopharyngeal aspirates and urine, collected from patients with suspected measles were tested in parallel using IFA and nucleic acid testing using the SmartCycler(®) and LightCycler(®) RT-PCR platforms. The LightCycler(®) RT-PCR was used as the reference assay against which the SmartCycler(®) RT-PCR and IFA were compared.

RESULTS

Using the LightCycler(®) RT-PCR, measles virus was detected in 35 clinical samples. There was 100% concordance between the results of the SmartCycler(®) and the LightCycler(®)-based RT-PCR. Measles genotypes detected included B3, D8, and D9. Testing urine in addition to NTS did not improve diagnostic yield. In contrast, the sensitivity and specificity of IFA compared to the reference LightCycler(®) RT-PCR was 34.3% and 96.7%, respectively.

CONCLUSION

The performance of the SmartCycler(®) is comparable to the LightCycler(®) for the detection of measles virus. However, IFA had poor sensitivity and should not be used to confirm measles virus infection where nucleic acid testing is available.

Double outbreak of measles in the talaja block of bhavnagar district, gujarat, India 2011: a need for improving the vaccine coverage and the community participation

BACKGROUND

Two outbreaks of measles were reported from an urban and a village area of Bhavnagar District, Gujarat, India in January and March 2011 respectively.

AIM

The present study was conducted to investigate and to assess various epidemiological features which were associated with the measles outbreak.

SETTINGS AND DESIGN

The present study was designed as a cross sectional study, which was conducted in an urban and a rural area of the Talaja block of the Bhavnagar district of Gujarat, India from December 2010 to April 2011.

METHODS AND MATERIAL

The suspected cases were detected through an active case finding in the community. We defined a case clinically by the WHO criteria as the occurrence of a febrile rash with or without cough, coryza and conjunctivitis in a resident of the Talaja-urban and the Gorkhi village of the Talaja block, in the period from 1(st) December 2010 to 30(th) April 2011. Blood samples from 10 case patients were collected for the IgM antibody detection. A community based, retrospective, cohort design was carried out to find the vaccine efficacy in the Gorkhi village.

STATISTICAL ANALYSIS

We entered and analyzed the data by using an MS-Excel sheet.

RESULTS

This study identified 27 confirmed cases of measles in the urban area of Talaja and 78 cases in Gorkhi village. All the 105 case patients belonged to the age group of 3 months-15 years. According to their mothers' statements, out of the 105 measles cases in the two areas, 40 (38%) case patients were immunized. Ten sera from five case-patients each from both the areas were tested; all were found to be positive for the IgM/IgG antibodies by ELISA.

CONCLUSIONS

The outbreaks occurred due to a poor community participation and the poor vaccine coverage levels.

Evaluating measles vaccines: can we assess cellular immunity?

Measles remains an important cause of childhood mortality, and global eradication of the disease is being seriously considered. Because of limitations of the current live-attenuated vaccines, new vaccines and routes of administration are being investigated. In the article under review, the authors have measured measles-specific humoral and cellular immune responses after two doses of live-attenuated measles vaccine and found limited correlation between the two. This study highlights an important issue, namely that we cannot assume humoral and cellular immune responses to go hand in hand. However, it remains to be determined if assays with peripheral blood lymphocytes can be used as a correlate of protection from disease.

The clinical epidemiology of pediatric patients with measles from 2000 to 2009 in shanghai, china

Measles remains a leading vaccine-preventable cause of child mortality worldwide. The incidence has increased recently in some areas. The authors retrospectively analyzed the epidemiological and clinical characteristics of 2473 measles patients in Shanghai from 2000 to 2009. There were 1909 measles cases during 2005-2009 (group II), whereas only 564 cases were reported during 2000-2004 (group I). In total, 60.87% patients in group II were younger than 9 months, which was significantly higher than that in group I (35.28%; P < .001). More complications, death cases, and less atypical rashes were found in recent years. In addition, 2181 of all the 2473 patients (88.19%) and 1112 of 1328 hospitalized children (83.73%) had not been vaccinated; most of them were immigrants. The results indicated that the rising number of immigrants accounted for the increased measles morbidity in Shanghai. The tendency of more young patients and increased complications suggest that some adjustments might be needed in vaccination administration and therapeutic strategy.

Risk analysis for measles reintroduction after global certification of eradication

BACKGROUND

Measles virus will continue to exist after certification of global eradication as virus stocks and infectious materials held in laboratories, in persistently and chronically infected individuals, and possibly in undetected foci of transmission. A literature search was undertaken to identify and evaluate the main risks for reintroduction of measles transmission in the absence of universal measles immunization.

METHODS

A qualitative risk assessment was conducted following a series of literature searches using the PubMed database.

RESULTS

If the criteria for global certification of eradication are stringent and require rigorous validation, then the risk of undetected measles transmission after certification is very low. Risk of unintentional reintroduction from any source, including persistent infections and laboratory materials is low to very low but depends on the extent of measles vaccine use. If immunization levels decrease, measles will become a credible agent for bioterrorism through intentional release.

CONCLUSIONS

Posteradication risks are low and should not deter any attempt at measles eradication. More information on measles transmission dynamics and the role of atypical infections is required to determine requirements for global certification of eradication. Posteradication risks would be minimized through development and implementation of an international risk management strategy, including requirements for a posteradication vaccine stockpile.

Laboratory characterization of measles virus infection in previously vaccinated and unvaccinated individuals

Waning immunity or secondary vaccine failure (SVF) has been anticipated by some as a challenge to global measles elimination efforts. Although such cases are infrequent, measles virus (MeV) infection can occur in vaccinated individuals following intense and/or prolonged exposure to an infected individual and may present as a modified illness that is unrecognizable as measles outside of the context of a measles outbreak. The immunoglobulin M response in previously vaccinated individuals may be nominal or fleeting, and viral replication may be limited. As global elimination proceeds, additional methods for confirming modified measles cases may be needed to understand whether SVF cases contribute to continued measles virus (MeV) transmission. In this report, we describe clinical symptoms and laboratory results for unvaccinated individuals with acute measles and individuals with SVF identified during MeV outbreaks. SVF cases were characterized by the serological parameters of high-avidity antibodies and distinctively high levels of neutralizing antibody. These parameters may represent useful biomarkers for classification of SVF cases that previously could not be confirmed as such using routine laboratory diagnostic techniques.

Two case studies of modified measles in vaccinated physicians exposed to primary measles cases: high risk of infection but low risk of transmission

In 2009, measles outbreaks in Pennsylvania and Virginia resulted in the exposure and apparent infection of 2 physicians, both of whom had a documented history of vaccination with >2 doses of measles-mumps-rubella vaccine. These physicians were suspected of having been infected with measles after treating patients who subsequently received a diagnosis of measles. The clinical presentation was nonclassical in regard to progression, duration, and severity. It is hypothesized that the 2 physicians mounted vigorous secondary immune responses typified by high avidity measles immunoglobulin G antibody and remarkably high neutralizing titers in response to intense and prolonged exposure to a primary measles case patient. Both of the physicians continued to see patients, because neither considered that they could have measles. Despite surveillance for cases among contacts, including unvaccinated persons, no additional cases were identified.

Investigation of measles IgM-seropositive cases of febrile rash illnesses in the absence of documented measles virus transmission, State of São Paulo, Brazil, 2000-2004

INTRODUCTION

To review measles IgM-positive cases of febrile rash illnesses in the State of São Paulo, Brazil, over the five-year period following interruption of measles virus transmission.

METHODS

We reviewed 463 measles IgM-positive cases of febrile rash illness in the State of São Paulo, from 2000 to 2004. Individuals vaccinated against measles < or = 56 days prior to specimen collection were considered to be exposed to the vaccine. Serum from the acute and convalescent phases was tested for evidence of measles, rubella, parvovirus B19 and human herpes virus-6 infection. In the absence of seroconversion to measles immunoglobulin-G, measles IgM-positive cases were considered false positives in individuals with evidence of other viral infections.

RESULTS

Among the 463 individuals with febrile rash illness who tested positive for measles IgM antibodies during the period, 297 (64%) were classified as exposed to the vaccine. Among the 166 cases that were not exposed to the vaccine, 109 (66%) were considered false positives based on the absence of seroconversion, among which 21 (13%) had evidence of rubella virus infection, 49 (30%) parvovirus B19 and 28 (17%) human herpes virus-6 infection.

CONCLUSIONS

Following the interruption of measles virus transmission, thorough investigation of measles IgM-positive cases is required, especially among cases not exposed to the vaccine. Laboratory testing for etiologies of febrile rash illness aids interpretation of these cases.

Detection of measles virus RNA on SYBR green real-time reverse transcription-polymerase chain reaction

BACKGROUND

As the coverage rate of the measles vaccine increases, not all patients present the typical symptoms of measles after exposure to the measles virus (MV). The virus loads in clinical specimens from patients with vaccine-modified non-typical measles are expected to be low compared with those of primary MV infection. A rapid and sensitive laboratory procedure is required for diagnosis of measles.

METHODS

SYBR Green (TaKaRa) and TaqMan (ABI) real-time reverse transcription-polymerase chain reaction (RT-PCR) assays were developed to detect MV-RNA. For the real-time RT-PCR, primer sets were designed from a region of the MV H gene of the Edmonston strain (genotype A). A TaqMan probe specific for the H gene of genotype D MV was used. The minimum detectable level of MV-RNA in the SYBR Green and TaqMan real-time RT-PCR assays was evaluated using synthetic MV-RNA. The sensitivity of real-time RT-PCR was compared with that of nested RT-PCR and the virus isolation method using throat swabs and peripheral blood samples from patients with measles.

RESULTS

The minimum detectable level of RNA was 10 and 10(2) copies for SYBR Green RT-PCR and TaqMan RT-PCR, respectively. Ten-10(6) copies of standard RNA were linearly detected on SYBR Green RT-PCR. The sensitivity of SYBR Green RT-PCR was equal to that of nested RT-PCR. MV-RNA was detected in virus isolation-negative throat swabs on SYBR Green RT-PCR.

CONCLUSION

SYBR Green RT-PCR is a highly sensitive, rapid, and useful diagnostic procedure for the detection of MV.

[Elimination of measles plan in the Valencia community: epidemiological surveillance in 2003]

AIMS

Describing the clinical and epidemiological characteristics of the suspicions of measles notified in the CV during the year 2003 and evaluating the system of surveillance.

DESIGN

Cross-sectional, descriptive study.

SETTING

Community of Valencia (CV), Spain.

PARTICIPANTS

Cases of suspected measles notified in 2003.

MAIN MEASUREMENTS

Description of the data collected in the questionnaires (including names) of the Plan to Eliminate Measles of the CV, and obtaining of quality indicators for this plan and those proposed in the national action plan.

RESULTS

From 43 notified suspicions, 11 (25.6%) were confirmed, 29 (67.4%) discarded, and 3 (7%) compatible. The rate of effect was 0.33 of 105. From 11 confirmed cases, 10 belonged to two outbreaks (one familiar and an other one communitary) and one was an isolated and imported case. 80% of areas of health were declared. The majority of the suspicions and all the cases were given in the first half of the year. Five cases were given in cohorts of age not submitted to the program of vaccination (minors of 15 months and major of 20 years), and 2 cases might have been avoidable in agreement with the program (6 and 12-year-old children not vaccinated). 40 samples of whey and 33 of urine were collect within the recommended periods. The majority of quality indicators were over the recommended ones (80%).

CONCLUSIONS

In year 2003 no case of measles has taken place from autochthonous virus in the CV.

A simple method for the detection of measles virus genome by loop-mediated isothermal amplification (LAMP)

Approximately 20,000-30,000 measles patients were reported in a surveillance of infectious diseases because of low vaccine coverage of 80% in Japan. Among them, some were thought to be secondary vaccine failure (SVF) with generally mild or non-typical measles illness and sometimes became a source of further transmission. We have developed a new, sensitive, and rapid method to detect the measles virus genome by reverse transcription loop-mediated isothermal amplification (RT-LAMP). We examined 50 nasopharyngeal secretion (NPS) samples that were obtained during the 1999 outbreak and stored at -70 degrees C and fresh NPS, lymphocytes and sera from 11 patients in 2003. Total RNA was extracted from the samples and subjected to reverse transcription-polymerase chain reaction (RT-PCR) and RT-LAMP. We detected the genomic RNA corresponding to at least 0.01-0.04 TCID50, 30-100 copies in samples by RT-LAMP within 60 min after extraction of RNA, and all four genotypes isolated in Japan were equally amplified. Specific DNA amplification was monitored spectrophotometrically by real time turbidimeter and the quantity of RNA was calculated. Measles virus genome was detected in 44 of 50 stored NPS by RT-PCR and in 49 by RT-LAMP. The vaccine strain was discriminated from wild strains after sequencing the LAMP products. RT-LAMP is a useful rapid diagnostic method for the detection of measles virus without any special apparatus, showing higher sensitivity than RT-PCR, and expected to be applied for hospital-based infection control and for laboratory-based measles surveillance.

Modelling measles re-emergence as a result of waning of immunity in vaccinated populations

An age-structured mathematical model of measles transmission in a vaccinated population is used to simulate the shift from a population whose immunity is derived from natural infection to a population whose immunity is vaccine-induced. The model incorporates waning of immunity in a population of vaccinees that eventually will become susceptible to a milder form of vaccine-modified measles with a lower transmission potential than unvaccinated classical measles. Using current estimates of duration of vaccine-derived protection, measles would not be expected to re-emerge quickly in countries with sustained high routine vaccine coverage. However, re-emergence is possible to occur several decades after introduction of high levels of vaccination. Time until re-emergence depends primarily on the contagiousness of vaccine-modified measles cases in comparison to classical measles. Interestingly, in a population with a high proportion of vaccinees, vaccine-modified measles and classical measles would occur essentially in the same age groups. Although waning of humoral immunity in vaccinees is widely observed, re-emergence of measles in highly vaccinated populations depends on parameters for which better estimates are needed.

Lack of Evidence of Measles Virus Shedding in People with Inapparent Measles Virus Infections

Serological evidence of measles virus infection has been detected among people exposed to measles who do not exhibit classical clinical symptoms. Throat swabs, lymphocytes, and serum and urine samples were collected from contacts of individuals with confirmed measles 12-16 days after exposure, during measles outbreaks occurring in 1998. Follow-up serum samples were drawn 2 weeks later. Samples were tested for measles IgM antibody by enzyme immunoassays and plaque reduction neutralization testing. Virus isolation and reverse transcriptase-polymerase chain reaction testing was attempted for all samples. None of the 133 contacts developed classical measles disease; 11 (8%) had serological evidence of infection. Duration of exposure of >or=3 h was the only significant risk factor for developing serological response (24% vs. 4% among contacts exposed for 1-2 h; relative risk, 6.0; 95% confidence interval, 1.9-19.2). None of the 133 contacts had virological evidence of infection by culture or polymerase chain reaction. We found no evidence that persons with inapparent measles virus infections shed measles virus.

Epidemiology of Measles in the United States, 1997-2001

Of the 540 measles cases (annual incidence, less than 1/million population) reported during 1997-2001 in the United States, 362 (67%) were associated with international importation: 196 imported cases, 138 cases epidemiologically linked to imported cases, and 28 cases associated with an imported measles virus genotype. The remaining 178 (33%) "unknown-source" cases were analyzed as potential evidence of endemic measles transmission. A total of 83 counties (2.6% of the 3140 US counties) in 27 states reported unknown-source cases; 49 counties reported only 1 unknown-source case, and the maximum reported by any county was 10. Nationally, unknown-source cases were reported in 103 of the 260 weeks. The largest unknown-source outbreak included 13 cases and lasted 5 weeks. The rarity of unknown-source cases, wide gaps in geographic and temporal distribution, and the short duration of the longest unknown-source outbreak indicate that endemic transmission of measles was not sustained in the United States during this period.

Antibody dynamics in childhood diseases: waning and boosting of immunity and the impact of vaccination

The introduction of vaccination against acute diseases such as measles induced a dramatic decline in the prevalence of the disease, and a more gradual rise in the proportion of the population whose immunity is derived solely from vaccination. These two factors combine to constitute an important shift in the dynamics of immunity, especially in highly vaccinated populations. We develop a general model to describe both loss of immunity in the absence of disease, and boosting of immunity corresponding to subclinical infection in individuals whose immunity has waned. We consider the interaction between infection and immunity and identify the key parameters that determine the eradication threshold. We explore the dynamics in the years following the introduction of vaccination using a stochastic version of the model, and consider the effect of different assumptions concerning the nature of immunity. A comparison of the model results with recently published data suggests that heterogeneity in host immune response is an important feature of the antibody dynamics.

Detection of measles virus genome in bone-marrow aspirates from adults

We investigated the presence of the measles virus genome in order to identify asymptomatic infections in the adult population. Bone-marrow aspirates were obtained from 179 patients, 20-96 years of age, for the diagnosis of malignant diseases (29 with malignant lymphoma, 28 with acute leukaemia, 21 with myelodysplastic syndrome, five with multiple myeloma and 96 with other diseases). The measles virus genome was detected in 17 (9.5%) of 179 individuals by RT-PCR and 28 (15.6%) through hybridization. The genomes detected in bone marrow were all in the same cluster, D5, the strain circulating during the study period, and no evidence of persistent infection was obtained. We conclude that asymptomatic infections of measles virus are common in adults and the presence of the measles virus genome would not be related to the pathogenesis of illness.

Detection of measles virus genome in lymphocytes from asymptomatic healthy children

A total of 342 samples of peripheral blood mononuclear cells (PBMC) were obtained from 145 healthy individuals, which we examined for the presence of measles virus genome RNA by reverse transcription-polymerase chain reaction (RT-PCR), to identify whether asymptomatic infection of measles virus has occurred in healthy children. Measles virus genome was detected in 11 (23.4%) of 47 nonimmunized individuals; all positives for RT-PCR were infants who experienced measles exposure. No genome was detected in those without measles exposure. In 83 individuals immunized with measles vaccine, the vaccine strain genome was detected in 10 (71.4%) of 14 recipients whose PBMC were obtained within 2 months of vaccination. Measles wild-type genome was detected in 36 (46.2%) of 78 individuals, 40 (25.2%) of 159 samples, who had been immunized more than 2 months before. The wild-type measles genome was also detected in 6 (46.2%) of 13 individuals who had been infected with measles in the distant past. The measles PCR-positive rate was not related to the period since immunization or natural infection. Sequence analysis of PCR products demonstrated they were all in the same cluster of D5 lineage, which was the circulating strain during the study period. We obtained 13 samples of nasopharyngeal secretion (NPS) simultaneously from individuals whose PBMC were positive for measles PCR but did not detect virus genome. Measles genome was, however, detected from NPS in cases of acute infection. We conclude that asymptomatic measles infection is common but would rarely become a source of transmission because of negative PCR in NPS.

Measles outbreak in a community with very low vaccine coverage, the Netherlands

A 1999-2000 measles epidemic in the Netherlands started with an outbreak in an orthodox reformed elementary school with 7% vaccine coverage. The overall attack rate was 37%: 213 clinical cases among the 255 participating pupils (response 62%) and 327 household members. The attack rate ranged from 0% for the oldest groups of pupils to 88% for the youngest, who had not been exposed in previous measles epidemics. None of 25 vaccinated pupils had clinical symptoms. Among pupils with clinical symptoms, the self-reported complication rate was 25%. These data confirm that measles infection causes severe disease and that vaccination is the most effective means of preventing the disease and its complications. The data also show that clusters of persons refraining from vaccination interfere with measles elimination even in populations with very high overall vaccine coverage (96%).

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.

Protective immunity in macaques vaccinated with a modified vaccinia virus Ankara-based measles virus vaccine in the presence of passively acquired antibodies

Recombinant modified vaccinia virus Ankara (MVA), encoding the measles virus (MV) fusion (F) and hemagglutinin (H) (MVA-FH) glycoproteins, was evaluated in an MV vaccination-challenge model with macaques. Animals were vaccinated twice in the absence or presence of passively transferred MV-neutralizing macaque antibodies and challenged 1 year later intratracheally with wild-type MV. After the second vaccination with MVA-FH, all the animals developed MV-neutralizing antibodies and MV-specific T-cell responses. Although MVA-FH was slightly less effective in inducing MV-neutralizing antibodies in the absence of passively transferred antibodies than the currently used live attenuated vaccine, it proved to be more effective in the presence of such antibodies. All vaccinated animals were effectively protected from the challenge infection. These data suggest that MVA-FH should be further tested as an alternative to the current vaccine for infants with maternally acquired MV-neutralizing antibodies and for adults with waning vaccine-induced immunity.

Serological and virological characterization of clinically diagnosed cases of measles in suburban Khartoum

Measles continues to be a major childhood disease in terms of global morbidity and mortality. In the main areas of its endemicity the only available means of diagnosis are based on clinical criteria: the presence of a maculopapular rash and fever accompanied by cough, coryza, and/or conjunctivitis. We have studied 38 clinically diagnosed cases of measles in Khartoum, Sudan, by means of serology, reverse transcriptase PCR (RT-PCR) on throat swabs and virus isolation from lymphocytes. On the basis of serology, 28 patients were diagnosed as having an acute measles virus (MV) infection, while in 10 cases the clinical symptoms proved to have other causes. It was shown that in cases with low serum immunoglobulin M (IgM) levels, an additional measurement of IgG or virus-neutralizing antibodies was necessary to discriminate between patients with an acute MV infection sampled during an early stage of the disease and patients who had experienced an MV infection in the more distant past. The serological laboratory diagnosis was validated by an MV-specific RT-PCR: for all confirmed measles cases tested a fragment of the correct size which hybridized with a third MV-specific primer could be amplified, while all serologically negative cases were also RT-PCR negative. MV could be isolated from 17 out of 23 of the serologically confirmed cases, demonstrating that virus isolation is less reliable as a diagnostic tool than serology or RT-PCR. This study stresses the urgent need for a rapid diagnostic field test for measles.