Verification of measles elimination in Australia: Application of World Health Organization regional guidelines

A Cross-Sectional Study of Measles-Specific Antibody Levels in Australian Blood Donors-Implications for Measles Post-Elimination Countries

Passive immunisation with normal human immunoglobulin (NHIG) is recommended as post-exposure prophylaxis (PEP) for higher-risk measles contacts where vaccination is contraindicated. However, the concentration of measles-specific antibodies in NHIG depends on antibody levels within pooled donor plasma. There are concerns that measles immunity in the Australian population may be declining over time and that blood donors' levels will progressively decrease, impacting levels required to produce effective NHIG for measles PEP. A cross-sectional study of Australian plasmapheresis donors was performed using an age-stratified, random sample of recovered serum specimens, collected between October and November 2019 (n = 1199). Measles-specific IgG antibodies were quantified by ELISA (Enzygnost anti-measles virus IgG, Siemens), and negative and equivocal specimens (n = 149) also underwent plaque reduction neutralisation testing (PRNT). Mean antibody levels (optical density values) progressively decreased from older to younger birth cohorts, from 2.09 [±0.09, 95% CI] to 0.58 [±0.04, 95% CI] in donors born in 1940-1959 and 1990-2001, respectively (p < 0.0001). This study shows that mean measles-specific IgG levels are significantly lower in younger Australian donors. While current NHIG selection policies target older donors, as younger birth cohorts become an increasingly larger proportion of contributing donors, measles-specific antibody concentrations of NHIG will progressively reduce. We therefore recommend monitoring measles-specific antibody levels in future donors and NHIG products in Australia and other countries that eliminated measles before the birth of their youngest blood donors.

Global burden of 288 causes of death and life expectancy decomposition in 204 countries and territories and 811 subnational locations, 1990-2021: a systematic analysis for the Global Burden of Disease Study 2021

BACKGROUND

Regular, detailed reporting on population health by underlying cause of death is fundamental for public health decision making. Cause-specific estimates of mortality and the subsequent effects on life expectancy worldwide are valuable metrics to gauge progress in reducing mortality rates. These estimates are particularly important following large-scale mortality spikes, such as the COVID-19 pandemic. When systematically analysed, mortality rates and life expectancy allow comparisons of the consequences of causes of death globally and over time, providing a nuanced understanding of the effect of these causes on global populations.

METHODS

The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 cause-of-death analysis estimated mortality and years of life lost (YLLs) from 288 causes of death by age-sex-location-year in 204 countries and territories and 811 subnational locations for each year from 1990 until 2021. The analysis used 56 604 data sources, including data from vital registration and verbal autopsy as well as surveys, censuses, surveillance systems, and cancer registries, among others. As with previous GBD rounds, cause-specific death rates for most causes were estimated using the Cause of Death Ensemble model-a modelling tool developed for GBD to assess the out-of-sample predictive validity of different statistical models and covariate permutations and combine those results to produce cause-specific mortality estimates-with alternative strategies adapted to model causes with insufficient data, substantial changes in reporting over the study period, or unusual epidemiology. YLLs were computed as the product of the number of deaths for each cause-age-sex-location-year and the standard life expectancy at each age. As part of the modelling process, uncertainty intervals (UIs) were generated using the 2·5th and 97·5th percentiles from a 1000-draw distribution for each metric. We decomposed life expectancy by cause of death, location, and year to show cause-specific effects on life expectancy from 1990 to 2021. We also used the coefficient of variation and the fraction of population affected by 90% of deaths to highlight concentrations of mortality. Findings are reported in counts and age-standardised rates. Methodological improvements for cause-of-death estimates in GBD 2021 include the expansion of under-5-years age group to include four new age groups, enhanced methods to account for stochastic variation of sparse data, and the inclusion of COVID-19 and other pandemic-related mortality-which includes excess mortality associated with the pandemic, excluding COVID-19, lower respiratory infections, measles, malaria, and pertussis. For this analysis, 199 new country-years of vital registration cause-of-death data, 5 country-years of surveillance data, 21 country-years of verbal autopsy data, and 94 country-years of other data types were added to those used in previous GBD rounds.

FINDINGS

The leading causes of age-standardised deaths globally were the same in 2019 as they were in 1990; in descending order, these were, ischaemic heart disease, stroke, chronic obstructive pulmonary disease, and lower respiratory infections. In 2021, however, COVID-19 replaced stroke as the second-leading age-standardised cause of death, with 94·0 deaths (95% UI 89·2-100·0) per 100 000 population. The COVID-19 pandemic shifted the rankings of the leading five causes, lowering stroke to the third-leading and chronic obstructive pulmonary disease to the fourth-leading position. In 2021, the highest age-standardised death rates from COVID-19 occurred in sub-Saharan Africa (271·0 deaths [250·1-290·7] per 100 000 population) and Latin America and the Caribbean (195·4 deaths [182·1-211·4] per 100 000 population). The lowest age-standardised death rates from COVID-19 were in the high-income super-region (48·1 deaths [47·4-48·8] per 100 000 population) and southeast Asia, east Asia, and Oceania (23·2 deaths [16·3-37·2] per 100 000 population). Globally, life expectancy steadily improved between 1990 and 2019 for 18 of the 22 investigated causes. Decomposition of global and regional life expectancy showed the positive effect that reductions in deaths from enteric infections, lower respiratory infections, stroke, and neonatal deaths, among others have contributed to improved survival over the study period. However, a net reduction of 1·6 years occurred in global life expectancy between 2019 and 2021, primarily due to increased death rates from COVID-19 and other pandemic-related mortality. Life expectancy was highly variable between super-regions over the study period, with southeast Asia, east Asia, and Oceania gaining 8·3 years (6·7-9·9) overall, while having the smallest reduction in life expectancy due to COVID-19 (0·4 years). The largest reduction in life expectancy due to COVID-19 occurred in Latin America and the Caribbean (3·6 years). Additionally, 53 of the 288 causes of death were highly concentrated in locations with less than 50% of the global population as of 2021, and these causes of death became progressively more concentrated since 1990, when only 44 causes showed this pattern. The concentration phenomenon is discussed heuristically with respect to enteric and lower respiratory infections, malaria, HIV/AIDS, neonatal disorders, tuberculosis, and measles.

INTERPRETATION

Long-standing gains in life expectancy and reductions in many of the leading causes of death have been disrupted by the COVID-19 pandemic, the adverse effects of which were spread unevenly among populations. Despite the pandemic, there has been continued progress in combatting several notable causes of death, leading to improved global life expectancy over the study period. Each of the seven GBD super-regions showed an overall improvement from 1990 and 2021, obscuring the negative effect in the years of the pandemic. Additionally, our findings regarding regional variation in causes of death driving increases in life expectancy hold clear policy utility. Analyses of shifting mortality trends reveal that several causes, once widespread globally, are now increasingly concentrated geographically. These changes in mortality concentration, alongside further investigation of changing risks, interventions, and relevant policy, present an important opportunity to deepen our understanding of mortality-reduction strategies. Examining patterns in mortality concentration might reveal areas where successful public health interventions have been implemented. Translating these successes to locations where certain causes of death remain entrenched can inform policies that work to improve life expectancy for people everywhere.

FUNDING

Bill & Melinda Gates Foundation.

Measles, mumps, rubella and varicella antibodies among international and domestic university students

BACKGROUND

Vaccine-preventable infections are generally well controlled in Australia. However, gaps in immunity can lead to outbreaks and are important to identify. Young adults are a highly mobile population and a potential source of imported infections. We aimed to evaluate anti- measles, mumps, rubella and varicella (MMR&V) IgG seroprevalence and explore factors relating to antibody seropositivity.

METHODS

A cross-sectional online survey was conducted among students from a large Australian university to collect demographic, vaccination, infection and travel characteristics. Blood samples were collected to measure MMR&V seroprevalence. Logistic regression was used to identify factors associated with seropositivity.

RESULTS

Among 804 university students, seroprevalence (positive or equivocal) for measles was 82.3% (95% CI 79.6-84.8%), mumps 79.5% (95% CI 76.7-82.3%), rubella 91.5% (95% CI 89.6-93.5%) and varicella 86.2% (95% CI 84.1-88.8%), with 452 (56.2%, 95% CI 52.8-59.6) seropositive to all four viruses. Varicella seropositivity was highest in the older birth cohort (born 1988-1991). Measles seropositivity was higher for international students compared to domestic students. Among international students, mumps seroprevalence was significantly lower than measles and rubella seroprevalence. International travel in the previous 12 months was reported by 63.1% of students, but only 18.2% of travellers reported seeking pre-travel health advice prior to most recent international travel.

CONCLUSIONS

Overall, this study suggests immunity to MMR&V is sub-optimal. We found the university student population to be highly mobile and unlikely to seek pre-travel advice; thus, they are a potential source of infection importation. The implementation of university immunization policies could address the gaps identified and our findings can inform the development of targeted vaccination campaigns.

Australia's notifiable disease status, 2016: Annual report of the National Notifiable Diseases Surveillance System

Abstract

In 2016, a total of 67 diseases and conditions were nationally notifiable in Australia. The states and territories reported 330,387 notifications of communicable diseases to the National Notifiable Diseases Surveillance System. Notifications have remained stable between 2015 and 2016. In 2016, the most frequently notified diseases were vaccine preventable diseases (139,687 notifications, 42% of total notifications); sexually transmissible infections (112,714 notifications, 34% of total notifications); and gastrointestinal diseases (49,885 notifications, 15% of total notifications). Additionally, there were 18,595 notifications of bloodborne diseases; 6,760 notifications of vectorborne diseases; 2,020 notifications of other bacterial infections; 725 notifications of zoonoses and one notification of a quarantinable disease.

Emergence of Attenuated Measles Illness Among IgG-positive/IgM-negative Measles Cases: Victoria, Australia, 2008-2017

BACKGROUND

Waning measles immunity among vaccinated individuals may result in an attenuated illness. This study compares the epidemiological, clinical, and laboratory profile of measles cases with waning immunity with other measles cases.

METHODS

Polymerase chain reaction-positive (+) measles cases notified to Victoria's Department of Health and Human Services from 2008 to 2017 with immunoglobulin (Ig) M and IgG tested at diagnosis were classified according to serology at diagnosis: IgG negative (-) (nonimmune), IgM+/IgG+ (indeterminate), or IgM-/IgG+ (waning immunity).

RESULTS

Between 2008 and 2017, 297 measles cases were notified, of whom 190 (64%) were included; 151 of 190 (79%) were nonimmune at diagnosis, 26 (14%) were indeterminate, and 13 (7%) had waning immunity. Between 2008-2013 and 2014-2017, the proportion of cases with waning immunity increased from 0 of 87 (0%) to 13 of 103 (13%) (P < .001) and the diagnostic sensitivity of initial IgM fell from 93% to 81% (P = .012), respectively. Seven (54%) waning immunity cases reported receiving measles-containing vaccines; 1 case had 2 documented doses. Compared with nonimmune and indeterminate cases, waning immunity cases were more likely to be male; less likely to report fever, coryza, and cough; and had lower burden of virus (higher cycle threshold values). Waning immunity cases had higher IgG titers than indeterminate cases (mean optical density values, 1.96 vs 0.71; P = .004). Onward transmission from 1 waning immunity case was documented.

CONCLUSIONS

Waning immunity among measles cases, associated with secondary vaccine failure and modified clinical illness, is emerging in Victoria with transmission potential.

Is it or is it not? Lessons learned from a case of suspected vaccine strain measles

OBJECTIVE

Measles continues to be a threat to Australia. While post-eradication risks are low, imported measles cases from overseas travellers who are non-immune can cause small outbreaks. This case report discusses the challenge of identifying wild-type measles in an individual who was recently vaccinated with measles-containing vaccine (MCV).

METHODS

A positive polymerase chain reaction (PCR) result for measles for an adult who had recently received a measles-containing vaccine was notified. Investigation revealed no known epidemiological link, recent overseas travel or contact with recent measles cases during the incubation period.

RESULTS

The results of the initial sequencing to distinguish between wild-type and vaccine-strain measles were inconclusive. A decision was made to re-run the genotyping, collect additional specimens and quarantine the case until a definitive result was obtained. Sequencing and genotyping revealed that this indeed was a wild-type measles strain.

CONCLUSIONS

Changing epidemiology of measles means distinguishing between wild-type and vaccine-strain measles has become a new challenge. Implications for public health: The reflection of the public health management of this case has provided a valuable teaching tool for public health professionals globally, particularly in low incidence measles countries.

Clinical experience of intramuscular immunoglobulin for measles prophylaxis in children: Is it practical?

Measles continues to be a public health concern world-wide. Vulnerable individuals including those in which vaccinations is contraindicated, may be reliant on normal human immunoglobulin (NHIG) prophylaxis in an aim to prevent disease. This paper will summarise and discuss a tertiary paediatric hospital's clinical experience and the practicalities of administering intramuscular (IM) NHIG to paediatric patients as per the current measles prophylaxis guidelines in Australia. Following potential exposure within the emergency department, 17 paediatric patients (0-15 years) were recommended IM NHIG for prophylaxis. The dose of NHIG ranged from 0.6 to 15 mL and required multiple (2-8) injections. Two patients required sedation for staff to safely administer the injections. Staff involved with these cases reported administering multiple injections to paediatric patients to be a traumatising experience. They also expressed views that the injection of large volumes via the IM route was an impractical method of administration. Based on this experience, we recommend intravenous immunoglobulin be considered when large volumes of NHIG are recommended intramuscularly.

Laboratory methods supporting measles surveillance in Queensland, Australia, 2010-2017

PURPOSE

Australia was officially recognised as having eliminated endemic measles transmission in 2014. Maintaining laboratory support for surveillance of vaccine-preventable diseases, such as measles, is an essential component of reaching and maintaining transmission-free status.

METHODOLOGY

Real-time and conventional PCR-based tools were used to detect, differentiate from measles vaccine virus (MeVV), and sequence fragments of measles viruses (MeV) identified from specimens collected in Queensland. Specimens were mostly from travellers who had visited or returned to Queensland from international or interstate sites or been in contact with a case from either group.

RESULTS

Between 2010 and 2017, 13 678 specimens were tested in our laboratory using real-time RT-PCR (RT-rPCR), identifying 533 positives. Most specimens were swabs (70.98 %) and urines (25.56 %). A MeVV RT-rPCR was used on request and identified 154 instances of MeVV. MeV-positive extracts were genotyped as required. Genotypes identified among sequenced specimens included B3, D4, D8, D9, G3, and H1 as well as members of clade A as expected from the detection of MeV among virus introductions due to global travel and vaccination.

CONCLUSION

We describe the workflow employed and results from our laboratory between 2010 and 2017 for the sensitive detection of MeV infection, supporting high-quality surveillance to ensure the maintenance of Australia's measles-free status.

Australia’s notifiable disease status, 2015: Annual report of the National Notifiable Diseases Surveillance System

In 2015, 67 diseases and conditions were nationally notifiable in Australia. States and territories reported a total of 320,480 notifications of communicable diseases to the National Notifiable Diseases Surveillance System, an increase of 16% on the number of notifications in 2014. In 2015, the most frequently notified diseases were vaccine preventable diseases (147,569 notifications, 46% of total notifications), sexually transmissible infections (95,468 notifications, 30% of total notifications), and gastrointestinal diseases (45,326 notifications, 14% of total notifications). There were 17,337 notifications of bloodborne diseases; 12,253 notifications of vectorborne diseases; 1,815 notifications of other bacterial infections; 710 notifications of zoonoses and 2 notifications of quarantinable diseases.

Status of Measles Elimination in Eleven Countries with High Routine Immunisation Coverage in The WHO African Region

BACKGROUND

Measles elimination is defined as the absence of endemic measles virus transmission in a defined geographic area for at least 12 months in the presence of a well-performing surveillance system. The WHO framework for verification of measles elimination indicates that the achievement of measles and/or rubella elimination should be verified for individual countries.

OBJECTIVE

We identified 11 high performing countries based on their first dose measles vaccination coverage, and looked at their performance across the various programmatic parameters, to see if they are ready to undertake the verification of measles elimination.

METHODS

We identified 11 countries with >90% measles first dose coverage for the most recent 5 years according to the WHO UNICEF estimates of national immunisation coverage. We analysed vaccination coverage and surveillance performance in these countries.

RESULTS

Algeria, Botswana, Gambia, Mauritius, Rwanda, Seychelles have maintained measles first dose (MCV1) coverage of 95% or more since 2011. In 2015, only Algeria, Cape Verde and Seychelles had coverage of 95% or more for the second dose of measles vaccine (MCV2). Of the 22 supplemental immunisation activities (SIAs) among the 11 countries, only 6 had administrative coverage of less than 95%. Only Rwanda and Lesotho attained the case-based surveillance performance targets in all the five years.

CONCLUSION

Despite their high routine first dose measles immunisation coverage, all of the 11 countries have some program gaps indicating that they do not meet all the criteria to undergo verification of elimination at this point. It is recommended for these countries to set up national verification committees as per the WHO framework for verification of measles elimination, in order to initiate the documentation and monitoring of progress, and to address programmatic gaps in the coming years.

Utility of a Stressed Single Nucleotide Polymorphism (SNP) Real-Time PCR Assay for Rapid Identification of Measles Vaccine Strains in Patient Samples

Rapid differentiation of wild-type measles virus from measles vaccine strains is crucial during a measles outbreak and in a measles elimination setting. A real-time reverse transcription-PCR (rRT-PCR) for the rapid detection of measles vaccine strains was developed with high specificity and sensitivity equivalent to that of traditional measles genotyping methods.

Rapid differentiation of wild-type measles virus from measles vaccine strains is crucial during a measles outbreak and in a measles elimination setting. A real-time reverse transcription-PCR (rRT-PCR) for the rapid detection of measles vaccine strains was developed with high specificity and sensitivity equivalent to that of traditional measles genotyping methods. The “stressed” minor groove binder-TaqMan probe design approach achieves specificity to vaccine strains only, without compromising sensitivity. This assay, without requiring sequence genotyping, has proved to be extremely useful in outbreak settings for over 4 years at the Regional Measles Reference Laboratory for the Western Pacific Region.

Monitoring of Surveillance Quality Indicators of Measles in Iranian Districts: Analysis of Measles Surveillance System 2014-2016

BACKGROUND

The elimination target for measles as an acute and contagious disease in Eastern Mediterranean Region (EMR) and Iran is planned by high-quality surveillance. We aimed to monitor the surveillance quality indicators of measles by in all districts of Iran during 2014-16.

STUDY DESIGN

A cross-sectional study.

METHODS

Four quality surveillance indicators of measles including non measles discarded rate, percent of suspected cases with adequate investigation, percent of adequate blood specimen collection and percent with timely availability of laboratory results were assessed in Iran. Surveillance data of measles were extracted from the measles surveillance system and the risk point score for each district was calculated based on WHO Risk Assessment Tool by a function of four indicators.

RESULTS

Overall, 14312 suspected cases and 322 districts were assessed and the risk points of measles' quality surveillance showed that 92.8% of Iranian districts were categorized as low risk, 2.8% medium risk, 0.62% high risk and 3.73% very high-risk category. The appropriate non measles discarded rate indicator was 87.3%. The percent of suspected cases with adequate investigation (more than 2 per 100000 people) was 87.9%. Moreover, the average of percent adequate blood specimen collection and percent with timely availability of laboratory results was 85.16% and 85.71%, respectively in all Iranian districts.

CONCLUSIONS

The surveillance quality indicators in Iran were good and higher than the WHO plans. Increasing the percentage of non-measles discarded rate could improve the poor quality in high risk and very high-risk districts.

Measles control in Australia - threats, opportunities and future needs

Control of measles was the focus of a national workshop held in 2015 in Sydney, Australia, bringing together stakeholders in disease control and immunisation to discuss maintaining Australia's measles elimination status in the context of regional and global measles control. The global epidemiology of measles was reviewed, including outbreaks in countries that have achieved elimination, such as the Disneyland outbreak in the United States and large outbreaks in Sydney, Australia. Transmission of measles between Australia and New Zealand occurs, but has not been a focus of control measures. Risk groups, the genetic and seroepidemiology of measles as well as surveillance, modelling and waning vaccine-induced immunity were reviewed. Gaps in policy, research and practice for maintaining measles elimination status in Australia were identified and recommendations were developed. Elimination of measles globally is challenging because of the infectiousness of measles and the need for 2-dose vaccine coverage rates in excess of 95% in all countries to achieve it. Until this occurs, international travel will continue to permit measles importation from endemic countries to countries that have achieved elimination. When measles cases are imported, failure to diagnose and isolate cases places the health system at risk of measles outbreaks. Vaccine funding models can result in gaps in vaccine coverage for adults and migrants. Australia introduced a whole-of-life immunisation register in 2016 and catch-up vaccination for at-risk communities, which will improve measles control. Research on diagnosis, immunology, case management and modelling of vaccination strategies are important to ensure continued control of measles.

Public health response to a measles outbreak on a university campus in Australia, 2015

This report describes the effective public health response to a measles outbreak involving a university campus in Brisbane, Australia. Eleven cases in total were notified, mostly university students. The public health response included targeted measles vaccination clinics which were established on campus and focused on student groups most likely to have been exposed. The size of the university population, social interaction between students on and off campus, as well as limited vaccination records for the university community presented challenges for the control of this extremely infectious illness. We recommend domestic students ensure vaccinations are current prior to matriculation. Immunisation information should be included in university student enrolment packs. Incoming international students should ensure routine vaccinations are up-to-date prior to arrival in Australia, thereby reducing the risk of importation of measles and other infectious diseases.

Declining measles antibodies in the era of elimination: Australia's experience

BACKGROUND

Australia is one of only a few countries with a long-standing and consistent serosurveillance program. We conducted a national serosurvey in 2012-2013 to estimate population seroprevalence of measles-specific IgG and the effective reproduction number, R, and compare the results with the three previous serosurveys (1996-1999, 2002 and 2007) to examine trends following a decade of sustained measles control.

METHODS

2729 residual sera from 1 to 49 year olds were tested using the Enzygnost anti-measles IgG enzyme immunoassay (EIA). All sera in the equivocal range by EIA on re-testing and a random sample of low positive and negative sera were later tested by a microneutralisation assay. R was calculated from weighted estimates of the proportion seronegative by age using a previously developed contact matrix.

RESULTS

In the 2012-13 serosurvey, anti-measles IgG seropositivity for 1-49 year olds was 80.8% (95% CI: 79.4-82.3%) and 8.9% (95% CI: 7.8-10.0%) had equivocal antibody levels. The increasing proportion of seronegative and equivocal individuals in age groups 10-39 years continued a trend seen in previous serosurveys. There was also an increase in equivocal results among 2-4 and 5-9 year old children, >90% of whom were recently vaccinated. R increased from 0.57 in 1999 to above the epidemic threshold of 1 in 2012-13 (R = 1.7). All 20 EIA negative sera, 238/241 (98.8%) equivocal sera, and 89/92 (96.7%) low positive sera had a titre <10 (negative) in the measles microneutralisation assay.

CONCLUSIONS

A number of countries with sustained measles control have now demonstrated that measles-specific IgG antibodies decline with time since vaccination. As there is good epidemiologic evidence of population-level protection, the implications of declining measles-specific IgG antibody levels for maintaining measles elimination are unclear. Novel studies to determine correlates of protection against measles transmission and disease in the post-elimination era are needed to help answer this question.

Evaluation of Combination Measles-Mumps-Rubella-Varicella Vaccine Introduction in Australia

IMPORTANCE

Incorporating combination vaccines, such as the measles-mumps-rubella-varicella (MMRV) vaccine, into immunization schedules should be evaluated from a benefit-risk perspective. Use of MMRV vaccine poses challenges due to a recognized increased risk of febrile seizures (FSs) when used as the first dose in the second year of life. Conversely, completion by age 2 years of measles, mumps, rubella, and varicella immunization may offer improved disease control.

OBJECTIVE

To evaluate the effect on safety and coverage of earlier (age 18 months) scheduling of MMRV vaccine as the second dose of measles-containing vaccine (MCV) in Australia.

DESIGN, SETTING, AND PARTICIPANTS

Prospective active sentinel safety surveillance comparing the relative incidence (RI) of FSs in toddlers given MMRV and measles-mumps-rubella (MMR) and a national cohort study of vaccine coverage rates and timeliness before and after MMRV vaccine introduction were conducted. All Australian children aged 11 to 72 months were included in the coverage analysis, and 1471 Australian children aged 11 to 59 months were included in the FS analysis, with a focus on those aged 11 to 23 months.

MAIN OUTCOMES AND MEASURES

MMRV vaccine safety, specifically, the RI of FSs after MMRV vaccine at age 18 months, compared with risk following MMR vaccine and vaccine uptake for 2-dose MCV and single-dose varicella vaccine, focusing on timeliness.

RESULTS

Of the 1471 children, the median age at first FS was 21 months (interquartile range [IQR], 14-31 months). Three hundred ninety-one children were aged 11 to 23 months and had at least 1 FS included in the analysis; of these, 207 (52.9%) were male. A total of 278 children (71.1%) had received MMR followed by MMRV vaccine, 97 (24.8%) had received MMR vaccine only, and 16 (4.1%) had received neither vaccine. There was no increased risk of FSs (RI, 1.08; 95% CI, 0.55-2.13) in the 5 to 12 days following MMRV vaccine given as the second MCV to toddlers. Febrile seizures occurred after dose 1 of MMR vaccine at a known low increased risk (RI, 2.71; 95% CI, 1.71- 4.29). Following program implementation, 2-dose MCV coverage at age 36 months exceeded that obtained at age 60 months in historical cohorts recommended to receive MMR vaccine before school entry, and on-time vaccination increased by 13.5% (from 58.9% to 72.4%). Despite no change in the scheduled age of varicella vaccine, use of MMRV vaccine was associated with a 4.0% increase in 1-dose varicella vaccine coverage.

CONCLUSIONS AND RELEVANCE

To our knowledge, this is the first study to provide evidence of the absence of an association between use of MMRV vaccine as the second dose of MCV in toddlers and an increased risk of FSs. Incorporation of MMRV vaccine has facilitated improvements in vaccine coverage that will potentially improve disease control.

Prevention of treatable infectious diseases: A game-theoretic approach

We model outcomes of voluntary prevention using an imperfect vaccine, which confers protection only to a fraction of vaccinees for a limited duration. Our mathematical model combines a single-player game for the individual-level decision to get vaccinated, and a compartmental model for the epidemic dynamics. Mathematical analysis yields a characterization for the effective vaccination coverage, as a function of the relative cost of prevention versus treatment; note that cost may involve monetary as well as non-monetary aspects. Three behaviors are possible. First, the relative cost may be too high, so individuals do not get vaccinated. Second, the relative cost may be moderate, such that some individuals get vaccinated and voluntary vaccination alleviates the epidemic. In this case, the vaccination coverage grows steadily with decreasing relative cost of vaccination versus treatment. Unlike previous studies, we find a third case where relative cost is sufficiently low so epidemics may be averted through the use of prevention, even for an imperfect vaccine. However, we also found that disease elimination is only temporary-as no equilibrium exists for the individual strategy in this third case-and, with increasing perceived cost of vaccination versus treatment, the situation may be reversed toward the epidemic edge, where the effective reproductive number is 1. Thus, maintaining relative cost sufficiently low will be the main challenge to maintain disease elimination. Furthermore, our model offers insight on vaccine parameters, which are otherwise difficult to estimate. We apply our findings to the epidemiology of measles.