Sero-Prevalence Surveillance to Predict Vaccine-Preventable Disease Outbreaks; A Lesson from the 2014 Measles Epidemic in Northern Vietnam

Age-specific prevalence of IgG against measles/rubella and the impact of routine and supplementary immunization activities: A multistage random cluster sampling study with mathematical modelling

BACKGROUND

Vietnam continues to have measles and rubella outbreaks following supplementary immunization activities (SIA) and routine immunization despite both having high reported coverage. To evaluate immunization activities, age-specific immunity against measles and rubella, and the number of averted Congenital Rubella Syndrome (CRS) cases, must be estimated.

METHODS

Dried blood spots were collected from 2091 randomly selected individuals aged 1-39 years. Measles and rubella virus-specific immunoglobulin G (IgG) were measured by enzyme immunoassay. Results were considered positive at ≥120 mIU/mL for measles and ≥10 IU/mL for rubella. The number of CRS cases averted by immunization since 2014 were estimated using mathematical modelling.

RESULTS

Overall IgG seroprevalence was 99.7% (95%CI: 99.2-99.9) for measles and 83.6% (95%CI: 79.3-87.1) for rubella. Rubella IgG seroprevalence was higher among age groups targeted in the SIA than in non-targeted young adults (95.4% [95%CI: 92.9-97.0] vs 72.4% [95%CI: 63.1-80.1]; P < 0.001). The estimated number of CRS cases averted in 2019 by immunization activities since 2014 ranged from 126 (95%CI: 0-460) to 883 (95%CI: 0-2271) depending on the assumed postvaccination reduction in the force of infection.

CONCLUSIONS

The results suggest the SIA was effective, while young adults born before 1998 who remain unprotected for rubella require further vaccination.

Multiplex Bead Assay for the Serological Surveillance of Measles and Rubella

There is increasing interest in evaluating antibody responses to multiple antigen targets in a single assay. Immunity to measles and rubella are often evaluated together because immunity is provided through combined vaccines and because routine immunization efforts and surveillance for measles and rubella pathogens are combined in many countries. The multiplex bead assay (MBA) also known as the multiplex immunoassay (MIA) described here combines the measurement of measles- and rubella-specific IgG antibodies in serum quantitatively according to international serum standards and has been successfully utilized in integrated serological surveillance.

Immunity of Canadians and risk of epidemics workshop - Conference report

On November 18-19, 2019, the Immunity of Canadians and Risk of Epidemics (iCARE) Network convened a workshop in Toronto, Ontario, Canada. The objectives of the workshop were to raise the profile of sero-epidemiology in Canada, discuss best practice and methodological innovations, and strategize on the future direction of sero-epidemiology work in Canada. In this conference report, we describe the presentations and discussions from the workshop, and comment on the impact of the COVID-19 pandemic on serosurveillance initiatives, both in Canada and abroad.

Measles epidemic in Southern Vietnam: an age-stratified spatio-temporal model for infectious disease counts

Measles resurged in Vietnam between 2018 and 2020, especially in the Southern region. The proportion of children with measles infection showed quite some variation at the provincial level. We applied a spatio-temporal endemic-epidemic modelling framework for age-stratified infectious disease counts using measles surveillance data collected in Southern Vietnam between 1 January 2018 and 30 June 2020. We found that disease transmission within age groups was greatest in young children aged 0-4 years whereas a relatively high between-group transmission was observed in older age groups (5-14 years, 15-24 years and 25+ years groups). At the provincial level, spatial transmission followed an age-dependent distance decay with measles spread mainly depending on local and neighbouring transmission. Our study helped to clarify the measles transmission dynamics in a more detailed fashion with respect to age strata, time and space. Findings from this study may help determine proper strategies in measles outbreak control including promotion of age-targeted intervention programmes in specific areas.

Understanding the transmission dynamics of a large-scale measles outbreak in Southern Vietnam

OBJECTIVES

During 2018-2020, Southern Vietnam experienced a large measles outbreak of over 26,000 cases. We aimed to understand and quantify the measles spread in space-time dependence and the transmissibility during the outbreak.

METHODS

Measles surveillance reported cases between 1/2018 and 6/2020, vaccination coverage, and population data at provincial level were used. To illustrate the spatiotemporal pattern of disease spread, we employed the endemic-epidemic multivariate time series model decomposing measles risk additively into autoregressive, spatiotemporal, and endemic component. Likelihood-based estimation procedures were performed to determine the time-varying reproductive number R_e of measles.

RESULTS

Our analysis shows that measles incidence was associated with vaccination coverage heterogeneity and spatial interaction between provincial units. The risk of infections was dominated by between-province transmission (36.1% to 78.8%), followed by local endogenous transmission (4.1% to 61.5%) whereas the endemic behavior had a relatively small contribution (2.1% to 33.4%) across provinces. In the exponential phase of the epidemic, R_e was above the threshold with a maximum value of 2.34 (95%CI: 2.20-2.46).

CONCLUSION

Local vaccination coverage and human mobility are important factors contributing to the measles dynamics in Southern Vietnam and the high risk of inter-provincial transmission is of most concern. Strengthening disease surveillance is recommended, and further research is essential to understand the relative contribution of population immunity and control measures in measles epidemics.

COVID-19 Social Science and Public Engagement Action Research in Vietnam, Indonesia and Nepal (SPEAR): Protocol for a mixed methods study exploring the experiences and impacts of COVID-19 for healthcare workers and vulnerable communities

Background: When the novel coronavirus – SARS-CoV-2 – started to spread globally, there was a call for social and behavioral scientists to conduct research to explore the wider socio-cultural contexts of coronavirus disease 2019 (COVID-19), to understand vulnerabilities, as well as to increase engagement within communities to facilitate adoption of public health measures. In this manuscript, we describe the protocol for a study conducted in Indonesia, Nepal, and Vietnam. In the study, we explore how the COVID-19 pandemic is affecting individuals and their communities. We focus on the wider health and economic impacts of COVID-19, in particular emerging and increased burden on mental health, as well as new or deepened vulnerabilities in the communities. The introduction of vaccines has added another layer of complexity and highlights differences in acceptance and inequalities around access.  Methods: We use mixed methods, combining survey methods and social media surveillance to gain a picture of the general situation within each country, with in-depth qualitative methods to gain a deeper understanding of issues, coupled with a synergistic engagement component. We also include an exploration of the role of social media in revealing or driving perceptions of the pandemic more broadly. Participants include health workers and members of communities from 13 sites across the three countries. Data collection is spread across two phases. Phase 1 is concerned with exploring lived experiences, impacts on working lives and livelihoods, mental health and coping strategies. Phase 2 is concerned with acceptance of COVID-19 vaccines, factors that increase and reduce acceptance, and factors that influence access. Conclusions: We will disseminate findings in multiple ways including short reports and policy briefs, articles in peer-reviewed journals, and digital diaries will be edited into short films and uploaded onto social media sites.

Vaccine serocoverage under the expanded program on immunization among hill tribe children in Thailand: A cross-sectional study

BACKGROUND

Expanded programs on immunization (EPIs) are country-specific vaccine programs designed and implemented to prevent childhood diseases globally, including in Thailand. Hill tribe children in Thailand live in remote areas with underdeveloped education systems and low economic status. This study aimed to assess serocoverage under the EPI and access to vaccination clinics.

METHODS

A cross-sectional study was performed to assess serocoverage after childhood vaccination among hill tribe children who lived in 34 selected villages in Chiang Rai Province, Thailand. A validated questionnaire was administered, and 3-mL blood specimens were collected. Antibodies against hepatitis B surface antigen (anti-HBs), hepatitis B core antigen (anti-HBc), measles, Japanese encephalitis virus (JEV), and tetanus were detected. Chi-square tests were performed to detect the different proportion of patients with antibodies with different characteristics.

RESULTS

Half of the hill tribe children aged 1-18 years did not have medical evidence (logbook) of immunization. More than 98.0% of the children who had medical evidence received the recommended immunizations. Only half of the children had anti-HBs (51.1%), and 22.3% had antibodies against JEV. The majority were found to be positive for antibodies against measles (83.3%) and tetanus (91.4%). Sex (p-value = 0.028), tribe (p-value < 0.001), age (p-value < 0.001), and parents' monthly income (p-value = 0.008) were associated with a lack of medical evidence.

CONCLUSIONS

Existing immunization programs for hill tribe children in Thailand should be urgently evaluated and monitored for effectiveness.

Development of a Measles and Rubella Multiplex Bead Serological Assay for Assessing Population Immunity

Serosurveys are important tools for estimating population immunity and providing immunization activity guidance. The measles and rubella multiplex bead assay (MBA) offers multiple advantages over standard serological assays and was validated by comparison with the enzyme-linked immunosorbent assay (ELISA) and the measles plaque reduction neutralization (PRN) assay. Results from a laboratory-produced purified measles virus whole-virus antigen MBA (MeV WVA_L) correlated better with ELISA and PRN than results from the baculovirus-expressed measles nucleoprotein (N) MBA. Therefore, a commercially produced whole-virus antigen (MeV WVA_C) was evaluated. Serum IgG antibody concentrations correlated significantly with a strong linear relationship between the MeV WVA_C and MeV WVA_L MBAs (R = 0.962 and R ² = 0.926). IgG concentrations from the MeV WVA_C MBA showed strong correlation with PRN titers (R = 0.846), with a linear relationship comparable to values obtained with the MeV WVA_L MBA and PRN assay (R ² = 0.716 and R ² = 0.768, respectively). Receiver operating characteristic (ROC) curve analysis of the MeV WVA_C using PRN titer as the comparator resulted in a seroprotection cutoff of 153 mIU/ml, similar to the established correlate of protection of 120 mIU/ml, with a sensitivity of 98% and a specificity of 83%. IgG concentrations correlated strongly between the rubella WVA MBA and ELISA (R = 0.959 and R ² = 0.919). ROC analysis of the rubella MBA using ELISA as the comparator yielded a cutoff of 9.36 IU/ml, similar to the accepted cutoff of 10 IU/ml for seroprotection, with a sensitivity of 99% and a specificity of 100%. These results support use of the MBA for multiantigen serosurveys assessing measles and rubella population immunity.

The First 100 Days of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Control in Vietnam

Background

One hundred days after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first reported in Vietnam on 23 January, 270 cases were confirmed, with no deaths. We describe the control measures used by the government and their relationship with imported and domestically acquired case numbers, with the aim of identifying the measures associated with successful SARS-CoV-2 control.

Methods

Clinical and demographic data on the first 270 SARS-CoV-2 infected cases and the timing and nature of government control measures, including numbers of tests and quarantined individuals, were analyzed. Apple and Google mobility data provided proxies for population movement. Serial intervals were calculated from 33 infector-infectee pairs and used to estimate the proportion of presymptomatic transmission events and time-varying reproduction numbers.

Results

A national lockdown was implemented between 1 and 22 April. Around 200 000 people were quarantined and 266 122 reverse transcription polymerase chain reaction (RT-PCR) tests conducted. Population mobility decreased progressively before lockdown. In total, 60% (163/270) of cases were imported; 43% (89/208) of resolved infections remained asymptomatic for the duration of infection. The serial interval was 3.24 days, and 27.5% (95% confidence interval [CI], 15.7%-40.0%) of transmissions occurred presymptomatically. Limited transmission amounted to a maximum reproduction number of 1.15 (95% CI, .·37–2.·36). No community transmission has been detected since 15 April.

Conclusions

Vietnam has controlled SARS-CoV-2 spread through the early introduction of mass communication, meticulous contact tracing with strict quarantine, and international travel restrictions. The value of these interventions is supported by the high proportion of asymptomatic and imported cases, and evidence for substantial presymptomatic transmission.

The First 100 Days of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Control in Vietnam

BACKGROUND

One hundred days after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first reported in Vietnam on 23 January, 270 cases were confirmed, with no deaths. We describe the control measures used by the government and their relationship with imported and domestically acquired case numbers, with the aim of identifying the measures associated with successful SARS-CoV-2 control.

METHODS

Clinical and demographic data on the first 270 SARS-CoV-2 infected cases and the timing and nature of government control measures, including numbers of tests and quarantined individuals, were analyzed. Apple and Google mobility data provided proxies for population movement. Serial intervals were calculated from 33 infector-infectee pairs and used to estimate the proportion of presymptomatic transmission events and time-varying reproduction numbers.

RESULTS

A national lockdown was implemented between 1 and 22 April. Around 200 000 people were quarantined and 266 122 reverse transcription polymerase chain reaction (RT-PCR) tests conducted. Population mobility decreased progressively before lockdown. In total, 60% (163/270) of cases were imported; 43% (89/208) of resolved infections remained asymptomatic for the duration of infection. The serial interval was 3.24 days, and 27.5% (95% confidence interval [CI], 15.7%-40.0%) of transmissions occurred presymptomatically. Limited transmission amounted to a maximum reproduction number of 1.15 (95% CI, .·37-2.·36). No community transmission has been detected since 15 April.

CONCLUSIONS

Vietnam has controlled SARS-CoV-2 spread through the early introduction of mass communication, meticulous contact tracing with strict quarantine, and international travel restrictions. The value of these interventions is supported by the high proportion of asymptomatic and imported cases, and evidence for substantial presymptomatic transmission.

Comparison of Past Year Substance Use Estimates by Age, Sex, and Race/Ethnicity Between Two Representative Samples of the U.S. Adult Population

Comparative evaluations of national survey data can improve future survey design and sampling strategies thereby enhancing our ability to detect important population level trends. This paper presents differences in past year estimates of alcohol, cigarette, marijuana, and non-medical painkiller use prevalence by age, sex, and race/ethnicity between the 2012 National Survey on Drug Use and Health (NSDUH) and the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC-III) administered in 2012-2013. In general, estimates were higher for the NSDUH survey, but patterns of substance use prevalence were similar across race/ethnicity, age, and sex. Results show most significant differences in estimates, across substances, age groups, and sex were greatest among Hispanics, followed by non-Hispanic Whites, and non-Hispanic Blacks. Members of other racial/ethnic groups (e.g., Asian-American, Native American/Alaskan Native) were underrepresented in the NSDUH survey. In many cases, estimates for these subpopulations could not be calculated using the NSDUH data limiting our ability to draw comparisons with the NESARC estimates. Methodological differences in data collection for the NSDUH and NESARC surveys may have contributed to these findings. To promote effective population health surveillance methods, more work is needed to derive reliable and valid estimates from demographic subpopulations to better improve policymaking and intervention programming for at-risk populations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11113-021-09645-8.

Using models to shape measles control and elimination strategies in low- and middle-income countries: A review of recent applications

After many decades of vaccination, measles epidemiology varies greatly between and within countries. National immunization programs are therefore encouraged to conduct regular situation analyses and to leverage models to adapt interventions to local needs. Here, we review applications of models to develop locally tailored interventions to support control and elimination efforts. In general, statistical and semi-mechanistic transmission models can be used to synthesize information from vaccination coverage, measles incidence, demographic, and/or serological data, offering a means to estimate the spatial and age-specific distribution of measles susceptibility. These estimates complete the picture provided by vaccination coverage alone, by accounting for natural immunity. Dynamic transmission models can then be used to evaluate the relative impact of candidate interventions for measles control and elimination and the expected future epidemiology. In most countries, models predict substantial numbers of susceptible individuals outside the age range of routine vaccination, which affects outbreak risk and necessitates additional intervention to achieve elimination. More effective use of models to inform both vaccination program planning and evaluation requires the development of training to enhance broader understanding of models and where feasible, building capacity for modelling in-country, pipelines for rapid evaluation of model predictions using surveillance data, and clear protocols for incorporating model results into decision-making.

Plans for Nationwide Serosurveillance Network in Vietnam

In recent years, serosurveillance has gained momentum as a way of determining disease transmission and immunity in populations, particularly with respect to vaccine-preventable diseases. At the end of 2017, the Oxford University Clinical Research Unit and the National Institute of Hygiene and Epidemiology held a meeting in Vietnam with national policy makers, researchers, and international experts to discuss current seroepidemiologic projects in Vietnam and future needs and plans for nationwide serosurveillance. This report summarizes the meeting and the plans that were discussed to set up nationwide serosurveillance in Vietnam.

Antibodies against measles and rubella virus among different age groups in Thailand: A population-based serological survey

Measles and rubella are highly contagious viral diseases transmitted via respiratory secretions and aerosolized droplets. Thailand has implemented universal vaccination against measles using the monovalent measles (M) or the trivalent measles-mumps-rubella (MMR) vaccine for the past 30 years. Nevertheless, incidence of measles and rubella remains in some parts of the country. We conducted a seroprevalence study to evaluate the antibodies to measles and rubella virus among Thais of all ages and to determine pre-existing immunity resulting from either vaccination and/or natural exposure. A total of 1,781 serum samples collected in 2014 was tested for IgG to measles and rubella virus by commercial enzyme-linked immunosorbent assays (ELISA). Percentages of individuals with protective antibody levels and the geometric mean concentrations (GMC) of IgG in each age group were analysed. The GMC of anti-measles IgG and anti-rubella IgG were 653.7 IU/L (95% confidence interval (CI); 555.9–751.4) and 39.5 IU/mL (95% CI;35.0–43.9), respectively. Thais between the ages of six months and 25 years did not demonstrate sufficient protective herd immunity for measles. This observation is consistent with the recent measles outbreaks in this age group. Lower prevalence of immunity against rubella was found among children ages 5–6 years who may not have completed vaccination as infants. Our findings identify gaps in rubella and measles immunity in specific age groups and support recommendations for catch-up MMR vaccination in individuals 30 years of age or younger.