Assessing the transmission dynamics of measles in Japan, 2016

Measles Population Immunity in Hunan, China: A Serological Assessment

Background

Assessing the measles immunity profile is critical for developing effective nationwide or regionwide supplementary immunization activities (SIAs). This study aims to assess measles population immunity levels in China and investigate factors contributing to age-specific heterogeneities.

Methods

We conducted a cross-sectional population-based serological study in southern China between June and October 2021. We determined the population mean antibody concentration and seroprevalence by age and over time, along with their associated determinants. Moreover, we estimated the contact-adjusted immunity levels by considering both age-specific immunity levels and population contact rates.

Results

Among the 1015 study participants (aged 0-95 years), the overall seroprevalence was estimated at 80.9% (95% confidence interval [CI], 78.3-83.3). When adjusting for the age-specific contact rates, the contact-adjusted immunity was estimated at 66.8% (95% CI, 56.6-75.1). Individuals younger than age 30 years showed significantly lower antibody concentration and seroprevalence (mean log concentration: 5.9, seroprevalence: 73.6% [95% CI, 69.9-77.3]) compared to those older than age 50 years (mean log concentration: 6.8, seroprevalence: 96.8% [95% CI, 94.7-98.9]). In particular, individuals born after the last SIA (2010) showed a significantly faster waning of immunity.

Conclusions

Our findings highlight that immunity levels in the general population remain below the 95% threshold, underscoring the need for continued monitoring of immunity dynamics, especially for individuals born in a near-elimination setting and without subsequent SIAs.

Seroprevalence of Measles IgG Antibodies in Married Immigrant Women from Multicultural Families in Korea

BACKGROUND

Although an effective vaccine has been available, measles still causes mast morbidity and mortality world widely. In Korea, a small number of measles cases have been reported through exposure to imported cases among young people with vaccine-induced measles immunity. Recently due to international migration including marriage, marriage migrants were the second-largest group of foreign population in Korea. Our study was carried out to obtain positive rate of measles antibody among married immigrant women from 12 countries in 10 Gun-Counties and 6 Cities, Korea.

MATERIALS AND METHODS

A total of 547 blood samples were collected from maternal multicultural members from 12 countries. The measles-specific IgG antibody was measured by ELISA (Enzyme-linked immunosorbent assay; Enzygnost® Anti-measles virus/IgG, Siemens Healthcare Diagnostics Products GmbH, Marburg, Germany). We performed a simple logistic regression to test whether the measles antibody seroprevalence differed by participant age, location, or country of birth and then calculated the likelihood ratio statistics to determine whether measles antibody seroprevalence differed by country of birth.

RESULTS

Overall positive measles seroprevalence was 75.3% (95% confidence interval: 71.7 - 78.9). Participants aged 20 - 24 years, 25 - 29 years, and 30 - 63 years has respective seropositivities of 52.5%, 55.3%, and 82.7%. In this study, the geometric mean titers of participants aged 21 - 29 years were slightly lower than those of participants aged over 30 years, which were 1,372 mIU/ml and 2,261 mIU/ml, respectively (average of total participants: 2,027 mIU/ml).

CONCLUSION

The study provides detailed information about seroimmunity of the married immigrant population in Korea, which is important for measles elimination. Since the 1980s, most vaccine-preventable diseases including measles have been well-controlled. Nevertheless, sporadic measles outbreaks are still reported. Thus, special attention should be paid to the possible importation of infectious diseases such as measles by immigration.

Temporal Pattern of the Emergence of a Mutant Virus Escaping Cross-Immunity and Stochastic Extinction Within a Host

A high mutation rate of the RNA virus results in the emergence of novel mutants that may escape the immunity activated by the original (wild-type) strain. However, many of them go extinct because of the stochasticity due to the small initial number of infected cells. In a previous paper, we studied the probability of escaping stochastic extinction when the novel mutant has a faster rate of infection and when it is resistant to a drug that suppresses the wild-type virus. In this study, we examine the effect of escaping the immune reaction of the host. Based on a continuous-time branching process with time-dependent rates, we conclude the chance for a mutant strain to be established [Formula: see text] decreases with time [Formula: see text] since the wild-type infection when the mutant is produced. The number of novel mutants that can escape extinction risk has a peak soon after the wild-type infection. The number of novel escape mutations produced per patient in the early phase of host infection is small both for very strong and very weak immune responses, and it attains its maximum value when immune activity is of an intermediate strength.

An open-access database of infectious disease transmission trees to explore superspreader epidemiology

Historically, emerging and reemerging infectious diseases have caused large, deadly, and expensive multinational outbreaks. Often outbreak investigations aim to identify who infected whom by reconstructing the outbreak transmission tree, which visualizes transmission between individuals as a network with nodes representing individuals and branches representing transmission from person to person. We compiled a database, called OutbreakTrees, of 382 published, standardized transmission trees consisting of 16 directly transmitted diseases ranging in size from 2 to 286 cases. For each tree and disease, we calculated several key statistics, such as tree size, average number of secondary infections, the dispersion parameter, and the proportion of cases considered superspreaders, and examined how these statistics varied over the course of each outbreak and under different assumptions about the completeness of outbreak investigations. We demonstrated the potential utility of the database through 2 short analyses addressing questions about superspreader epidemiology for a variety of diseases, including Coronavirus Disease 2019 (COVID-19). First, we found that our transmission trees were consistent with theory predicting that intermediate dispersion parameters give rise to the highest proportion of cases causing superspreading events. Additionally, we investigated patterns in how superspreaders are infected. Across trees with more than 1 superspreader, we found preliminary support for the theory that superspreaders generate other superspreaders. In sum, our findings put the role of superspreading in COVID-19 transmission in perspective with that of other diseases and suggest an approach to further research regarding the generation of superspreaders. These data have been made openly available to encourage reuse and further scientific inquiry.

This study compiles and standardizes reported infectious disease transmission trees to analyze trends in superspreader frequency and generation; these data support theories that intermediate dispersion parameters give rise to the highest proportion of cases causing superspreading events, and that superspreaders generate other superspreaders.

Impact of virus genetic variability and host immunity for the success of COVID-19 vaccines

Coronavirus disease 19 (COVID-19) continues to challenge most scientists in the search of an effective way to either prevent infection or to avoid spreading of the disease. As result of global efforts some advances have been reached and we are more prepared today than we were at the beginning of the pandemic, however not enough to stop the transmission, and many questions remain unanswered. The possibility of reinfection of recovered individuals, the duration of the immunity, the impact of SARS-CoV-2 mutations in the spreading of the disease as well as the degree of protection that a potential vaccine could have are some of the issues under debate. A number of vaccines are under development using different platforms and clinical trials are ongoing in different countries, but even if they are licensed it will need time until reach a definite conclusion about their real safety and efficacy. Herein we discuss the different strategies used in the development of COVID-19 vaccines, the questions underlying the type of immune response they may elicit, the consequences that new mutations may have in the generation of sub-strains of SARS-CoV-2 and their impact and challenges for the efficacy of potential vaccines in a scenario postpandemic.

Measles and Rubella during COVID-19 Pandemic: Future Challenges in Japan

The coronavirus disease 2019 (COVID-19) pandemic has significantly impacted essential health services. Simultaneously, it has created opportunities for citizens to raise awareness of personal hygiene, mask wearing, and other preventive measures. This brief report aims to clarify the epidemiological trends of measles and rubella in Japan and to explore future challenges for controlling these diseases during and after the COVID-19 pandemic. Although Japan eliminated measles in 2015, the number of measles patients has gradually increased since then, and reached 744 in 2019. In the 2010s, Japan experienced two large rubella epidemics, and the majority of the patients were reported in Tokyo and other metropolitan areas. While the transmission of measles and rubella seems to be suppressed during the COVID-19 pandemic, closing the gap in routine childhood vaccination will be challenging in any country. Moreover, supplementary immunization campaigns for adults have also been disrupted, and they must be invigorated. While the pandemic has a devastating effect on a global scale, it should be utilized as a good opportunity to regain faith in vaccines, implement an evidence-based vaccination policy, and strengthen international cooperation.

Transmission Network of Measles During the Yamagata Outbreak in Japan, 2017

Background

A measles outbreak involving 60 cases occurred in Yamagata, Japan in 2017. Using two different mathematical models for different datasets, we aimed to estimate measles transmissibility over time and explore any heterogeneous transmission patterns.

Methods

The first model relied on the temporal distribution for date of illness onset for cases, and a generation-dependent model was applied to the data. Another model focused on the transmission network. Using the illness-onset date along with the serial interval and geographical location of exposure, we reconstructed a transmission network with 19 unknown links. We then compared the number of secondary transmissions with and without clinical symptoms or laboratory findings.

Results

Using a generation-dependent model (assuming three generations other than the index case), the reproduction number (R) over generations 0, 1, and 2 were 25.3, 1.3, and <0.1, respectively, explicitly yielding the transmissibility over each generation. The network data enabled us to demonstrate that both the mean and the variance for the number of secondary transmissions per primary case declined over time. Comparing primary cases with and without secondary transmission, high viral shedding was the only significant determinant (P < 0.01).

Conclusions

The R declined abruptly over subsequent generations. Use of network data revealed the distribution of the number of secondary transmissions per primary case and also allowed us to identify possible secondary transmission risk factors. High viral shedding from the throat mucosa was identified as a potential predictor of secondary transmission.

Identifying geographic areas at risk of rubella epidemics in Japan using seroepidemiological data

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Seroepidemiological data enabled us to compute the effective reproduction number.

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Risks of a major epidemic were high in areas with capital cities.

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Urban geographic areas possess small epidemic risk due to low volume of travelers.

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Urban areas have a large number of susceptible adult males aged 30–59 years.

Objective

Even with relatively high vaccination coverage, Japan experienced rubella epidemics in 2012–2014 and 2018–2019, which were fueled by untraced imported cases. We aimed to develop a risk map for rubella epidemics in Japan by geographic location via analysis of seroepidemiological data and accounting for the abundance of foreign visitors.

Methods

Geographic age distribution and seroprevalence were used to compute the age- and sex-dependent next-generation matrix in each region. We computed the probability of a major epidemic using the assumed number of untraced imported rubella cases proportionally modeled to the number of foreign travelers.

Results

Risks of a major epidemic were high in areas with capital cities, while areas with a greater fraction of older people yielded smaller effective reproduction numbers, a lower volume of foreign travelers, and thus a lower probability of a major epidemic. The volume of susceptible adult males was larger in urban geographic regions, having a greater number of foreign travelers than remote areas.

Conclusions

Our findings are consistent with the observation of multiple large clusters of rubella cases in urban areas during 2012–2014 and 2018–2019. Should a future rubella epidemic occur, it will likely be in geographic areas with capital cities.

Investigation and control of a measles outbreak at the Hong Kong Special Administrative Region International Airport, 2019

INTRODUCTION

Hong Kong Special Administrative Region SAR (China) achieved measles elimination status in 2016, and the incidence of measles infection had been low over the past few years. However, the Centre for Health Protection (CHP) at the Department of Health was notified on 22 March 2019 of an outbreak of three cases of measles infection among workers at the Hong Kong Special Administrative Region International Airport (HKIA).

METHODS

We reviewed notifications of measles received by CHP from 1 January to 17 May 2019. We defined a confirmed case of measles as having laboratory evidence of measles infection. All confirmed cases among airport workers or those with epidemiological information suggesting they had been infected by contact with airport workers were included in the review. We described the epidemiological features and reviewed the control measures against the outbreak.

RESULTS

We identified 33 cases, 29 of which were among airport workers. They comprised 22 men and 11 women, aged 20-49 years (median 25 years). The majority of people with confirmed measles presented with fever and rash. All required hospitalization. None developed complications. Control measures, including enhanced environmental hygiene and improved ventilation at HKIA and vaccinations for the airport community, were implemented. Vaccinations were provided to 8501 eligible airport workers, and the outbreak was declared over on 17 May 2019.

DISCUSSION

Early recognition of the outbreak and prompt control measures, especially targeted vaccination of the exposed population, effectively controlled the outbreak in just two weeks.

A Survey of Vaccine-Induced Measles IgG Antibody Titer to Verify Temporal Changes in Response to Measles Vaccination in Young Adults

In Japan, sporadic measles cases increased rapidly in 2019 compared to the past six years. To clarify the persistence of immunity against measles in young adults, this study explored the persistence of immunoglobulin G (IgG) antibody titers against the measles virus in 17- to 24-year-old young participants who reside in the Chiba prefecture of Japan. Measles-specific IgG antibody titers, determined by enzyme immunoassay in serum samples collected from 506 participants, were assessed through statistical analyses. Multivariable regression analysis revealed that the distribution of measles IgG antibody titers was significantly correlated with a medical history of measles (P < 0.05), while there was no significant correlation between the number of vaccinations related to measles IgG titers. Furthermore, measles IgG titers tended to decrease, as revealed by the temporal change in IgG titers, during the elapsed period after the last vaccination (P = 0.08). These results indicate that periodic vaccination against measles is required to prevent sporadic measles infection in young and older adults.

A case of adult rubella in Japan

We report the case of a 32-year-old Japanese female who presented with a mild sore throat, rash and posterior cervical and posterior auricular lymphadenopathy. She was diagnosed with rubella. Japan has experienced multiple outbreaks of rubella in recent times. Travelers to Japan should consider getting vaccinated for rubella.

Real Time Forecasting of Measles Using Generation-dependent Mathematical Model in Japan, 2018

Background: Japan experienced a multi-generation outbreak of measles from March to May, 2018. The present study aimed to capture the transmission dynamics of measles by employing a simple mathematical model, and also forecast the future incidence of cases.

Methods: Epidemiological data that consist of the date of illness onset and the date of laboratory confirmation were analysed. A functional model that captures the generation-dependent growth patterns of cases was employed, while accounting for the time delay from illness onset to diagnosis.

Results: As long as the number of generations is correctly captured, the model yielded a valid forecast of measles cases, explicitly addressing the reporting delay. Except for the first generation, the effective reproduction number was estimated by generation, assisting evaluation of public health control programs.

Conclusions: The variance of the generation time is relatively limited compared with the mean for measles, and thus, the proposed model was able to identify the generation-dependent dynamics accurately during the early phase of the epidemic. Model comparison indicated the most likely number of generations, allowing us to assess how effective public health interventions would successfully prevent the secondary transmission.

Measles vaccination in an increasingly immunized and developed world

Increased measles immunization has led to a significant decline in measles incidence and mortality. During 2016 it is estimated that fewer than 100,000 died from measles for the first time in recorded history. In highly immunized countries measles epidemiology has changed. Threats to national elimination goals and public health include aging cohorts of naïve people that exist from imperfect vaccination rates during the early years of immunization programs. This may be complemented by some loss of immunity in vaccinated populations. While childhood immunization must remain a focus for control efforts, due to higher mortality in the very young, these naïve adolescents and adults also accumulate as they age and add to the pool of susceptible people, perhaps beyond the view of those that are focused on childhood immunization. Here, features of measles epidemiology and control in highly immunized populations are reviewed, providing global data where necessary, to highlight why countries with high immunization coverage are still threatened by measles outbreaks and how changing dynamics may alter disease control.

An investigation of a measles outbreak in Japan and China, Taiwan, China, March-May 2018

Objective

To investigate a measles outbreak that spread to Japan and China, Taiwan, China during March–May 2018, exploring the characteristics of the super-spreading event.

Methods

A contact investigation of the index case and reconstruction of the epidemiological dynamics of measles transmission were conducted. Employing a mathematical model, the effective reproduction number was estimated for each generation of cases.

Results and discussion

A single index case gave rise to a total of 38 secondary cases, 33 in Japan and five in China, Taiwan, China. Subsequent chains of transmission were observed in highly vaccinated populations in both Japan and China, Taiwan, China. The effective reproduction number of the second generation was > 1 for both Japan and China, Taiwan, China. In Japan, the reproduction number was estimated to be < 1 during the third generation. Vaccination of susceptible individuals is essential to prevent secondary and tertiary transmission events.

Detection of modified measles and super-spreader using a real-time reverse transcription PCR in the largest measles outbreak, Yamagata, Japan, 2017 in its elimination era

We aimed to verify the effectiveness of real-time reverse transcription (rRT) polymerase chain reaction (PCR) for detecting cases of modified measles (M-Me) and for predicting super-spreader candidates through the experience of a measles outbreak dominated by M-Me in Yamagata, Japan, during March-April 2017. We applied rRT-PCR to specimens from 35 cases of M-Me, nine cases of typical measles (T-Me) and nine cases of prodromal stage of T-Me (P-Me). From rRT-PCR among the M-Me cases, peripheral blood mononuclear cells (PBMC) showed the highest positive rate (80.0%), followed by throat swab (48.6%), urine (33.3%) and serum (3.1%). The negative result of PBMC in M-Me cases was recovered by the result of a throat swab. In specimens of PBMC, throat swab and urine, M-Me group showed the significantly higher cycle of threshold (i.e., lower viral load) in the rRT-PCR than T-Me and P-Me groups, respectively. Furthermore, three super-spreaders in T-Me or P-Me showed an extremely low cycle of threshold in their throat swab specimens. rRT-PCR using PBMC and throat swab might be helpful for clinical management and measles control by certain detection of M-Me cases and by predicting super-spreading events resulting from measles cases with the high viral load.

Transmission potential of modified measles during an outbreak, Japan, March‒May 2018

A recent outbreak of measles in Okinawa Prefecture, Japan ended with 33 measles cases whose symptoms were masked because of insufficient protection against the disease (modified measles). Using quantitative modelling, we determined the transmission potential of measles by clinical presentation (classic vs modified measles). We found low ascertainment probabilities among modified measles cases, indicating that intensified public health interventions that specifically target this group should be implemented to better contain outbreaks with modified measles cases.

An increasing, potentially measles-susceptible population over time after vaccination in Korea

BACKGROUND

In Korea, measles occurs mainly in infants <12months of age, who are unvaccinated. In addition, vaccine populations, including adolescents and young adults, can become infected though importation. Thus, the question arises whether the current level of herd immunity in Korea is now insufficient for protecting against measles infection.

METHODS

Age-specific measles seroprevalence was evaluated by performing enzyme immunoassays and plaque reduction-neutralization tests on 3050 subjects aged 0-50years (birth cohort 1964-2014) and 480 subjects aged 2-30years (birth cohort 1984-2012).

RESULTS

The overall seropositivity and measles antibody concentrations were 71.5% and 1366mIU/mL, respectively. Progressive decline in antibody levels and seropositivity were observed over time after vaccination in infants, adolescents, and young adults. The accumulation of potentially susceptible individuals in the population was confirmed by comparing data from 2010 and 2014 seroprevalence surveys. The statistical correlation between measles incidence and measles seronegativity was determined.

CONCLUSIONS

Waning levels of measles antibodies with increasing time post-vaccination suggests that measles susceptibility is potentially increasing in Korea. This trend may be related to limitations of vaccine-induced immunity in the absence of natural boosting by the wild virus, compared to naturally acquired immunity triggered by measles infection. This study provides an important view into the current measles herd immunity in Korea.

Assessing age-dependent susceptibility to measles in Japan

BACKGROUND

Routine vaccination against measles in Japan started in 1978. Whereas measles elimination was verified in 2015, multiple chains of measles transmission were observed in 2016. We aimed to reconstruct the age-dependent susceptibility to measles in Japan so that future vaccination strategies can be elucidated.

METHODS

An epidemiological model was used to quantify the age-dependent immune fraction using datasets of vaccination coverage and seroepidemiological survey. The second dose was interpreted in two different scenarios, i.e., booster and random shots. The effective reproduction number, the average number of secondary cases generated by a single infected individual, and the age at infection were explored using the age-dependent transmission model and the next generation matrix.

RESULTS

While the herd immunity threshold of measles likely ranges from 90% to 95%, assuming that the basic reproductive number ranges from 10 to 20, the estimated immune fraction in Japan was below those thresholds in 2016, despite the fact that the estimates were above 80% for all ages. If the second dose completely acted as the booster shot, a proportion immune above 90% was achieved only among those aged 5years or below in 2016. Alternatively, if the second dose was randomly distributed regardless of primary vaccination status, a proportion immune over 90% was achieved among those aged below 25years. The effective reproduction number was estimated to range from 1.50 to 3.01 and from 1.50 to 3.00, respectively, for scenarios 1 and 2 in 2016; if the current vaccination schedule were continued, the reproduction number is projected to range from 1.50 to 3.01 and 1.39 to 2.78, respectively, in 2025.

CONCLUSION

Japan continues to be prone to imported cases of measles. Supplementary vaccination among adults aged 20-49years would be effective if the chains of transmission continue to be observed in that age group.