Estimation of measles vaccine efficacy and critical vaccination coverage in a highly vaccinated population

Mapping the Implementation Determinants of Second Dose Measles Vaccination in the World Health Organization African Region: A Rapid Review

The second dose of measles-containing vaccines (MCV2) has significant programmatic relevance in the current immunisation landscape because it serves as both an opportunity to reduce measles immunity gaps and strengthen second year of life vaccination platforms. However, MCV2 coverage remains suboptimal across countries in the World Health Organization (WHO) African Region and this puts a significant number of children at risk of morbidity and mortality from measles despite the availability of an effective vaccine. There is an urgent need to strengthen the implementation of MCV2 but this requires a thorough and systematic understanding of contextual factors that influence it. The literature that describes the determinants of implementation of MCV2 in a manner that adequately accounts for the complexity of the implementation context is scarce. Therefore, the purpose of this rapid review was to explore the implementation determinants of MCV2 in the WHO African Region using systems thinking. Literature search in two databases (PubMed and Google Scholar) were conducted. After screening, a total of 17 eligible articles were included in the study. Thematic analysis of extracted data was performed to identify the implementation determinants, after which they were mapped using the Consolidated Framework for Implementation Research (CFIR). A causal loop diagram (CLD) was used to illustrate the linkages between identified determinants. We found 44 implementation determinants across the five CFIR domains, i.e., innovation, outer setting, inner setting, individual, and implementation process. The majority of identified determinants are within the individual domain followed by the inner setting domain. The CLD showed that multiple contingent connections and feedback relationships exist between the identified implementation determinants within and across CFIR domains. The linkages between the implementation determinants revealed three balancing and reinforcing loops each. The findings suggest that implementation determinants of second-dose measles vaccination in the WHO African Region are complex, with multiple interconnections and interdependencies, and this insight should guide subsequent policies. There is an urgent need for further implementation research with embedded CLD in specific settings to inform the design of tailored systemic strategies to improve the implementation effectiveness of MCV2.

Risk Factors for Measles Nonimmunity in Rubella-Immune Pregnant Patients

OBJECTIVE

Measles immunity testing, unlike that for rubella, is not currently part of prenatal screening even though immunity to both is conferred by the measles-mumps-rubella (MMR) vaccine. Although endemic transmission of measles was declared eliminated in the United States in 2001, outbreaks have continued to occur. Given the risks associated with measles infection during pregnancy, we sought to identify risk factors for measles nonimmunity (MNI) in rubella-immune (RI) pregnant individuals.

METHODS

We performed a retrospective observational cross-sectional study of patients receiving prenatal care and delivering at two university hospitals and a county hospital in Southern California from April 1, 2019 to February 1, 2021. Inclusion criteria were pregnant individuals ≥18 years old who had serological testing for rubella and measles during pregnancy. Demographic data were extracted from electronic medical records, including results of serological testing and chronic medical conditions. All subjects were rubella immune, and we compared measles-immune (MI) with MNI groups.

RESULTS

In total, 1,813 RI individuals were identified, with 1,467 (81%) MI and 346 (19%) MNI individuals. Variables associated with an increased risk of MNI included having public health insurance (adjusted relative risk [aRR]: 1.56; 95% confidence interval [CI]: 1.24, 1.97) and Hispanic ethnicity (aRR: 1.37; 95% CI: 1.06, 1.78). Black race was associated with a decreased risk of MNI (aRR: 0.52; 95% CI: 0.29, 0.91). Birth year before 1989 demonstrated a trend toward increased risk of MNI, but this did not reach statistical significance (aRR 1.23; 95% CI: 1.00, 1.52). No differences were seen between the two groups for medical comorbidities.

CONCLUSION

Our study is the first to demonstrate risk factors for measles MNI in patients with documented rubella immunity. In the absence of universal measles serological screening recommendations, the risk factors identified could help guide clinicians in selective screening for those at risk of needing postpartum MMR vaccination.

KEY POINTS

· The rate of measles nonimmunity is higher than previously reported.. · Hispanic ethnicity and use of public insurance are risk factors for measles nonimmunity.. · The current recommendation for history-based screening for measles immunity is likely insufficient..

Impact of vaccination on the entire population and dose-response relation of COVID-19

Objective

The objective of this study is to develop a mathematical model for the COVID-19 pandemic including vaccination, the transmissibility of the virus-pathogen dose-response relationship, vaccine efficiency, and vaccination rate.

Methods

The Runge-Kutta (RK-45) method was applied to solve the proposed model with MATLAB code and the calculated results show the dynamics of the individuals in each compartment. The data of total death due to the COVID-19 pandemic in the case of the USA were collected from GitHub and the re-use of this data needs no ethical clearance. The control reproduction number was used to assess the dose-response relationship and critical vaccination coverage.

Results

We have calculated the probability of infection and the infection risk against the different exposure doses and the virus copies, respectively. The results show that the probability of infection increases with the increasing exposure dose for certain virus copies and the risk of infection decreases with the increasing of virus copies for a certain exposure dose. The results also show that the critical vaccination coverage demands increase with an increase in transmission rate and decrease with increasing vaccine efficacy.

Conclusions

It was seen that the critical vaccination coverage corresponding to an increased transmission rate rise sharply in the beginning and then reached a threshold. Moreover, the real data of the total death cases in the USA were compared with the fitted curved of the model which validated the proposed model. Vaccination against COVID-19 is essential to control the pandemic, and achieving high vaccine uptake in the population can reduce the pandemic as fast as possible.

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.

Fractional Dynamics of a Measles Epidemic Model

In this work, we replaced the integer derivative with Caputo derivative to model the transmission dynamics of measles in an epidemic situation. We began by recalling some results on the local and global stability of the measles-free equilibrium point as well as the local stability of the endemic equilibrium point. We computed the basic reproduction number of the fractional model and found that is it equal to the one in the integer model when the fractional order ν = 1. We then performed a sensitivity analysis using the global method. Indeed, we computed the partial rank correlation coefficient (PRCC) between each model parameter and the basic reproduction number R0 as well as each variable state. We then demonstrated that the fractional model admits a unique solution and that it is globally stable using the Ulam–Hyers stability criterion. Simulations using the Adams-type predictor–corrector iterative scheme were conducted to validate our theoretical results and to see the impact of the variation of the fractional order on the quantitative disease dynamics.

Vaccine Coverage Associated With Ending a Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Wave: A Retrospective Longitudinal Analysis

BACKGROUND

Two SARS-CoV-2 waves in Israel ended while a substantial number of individuals remained unvaccinated or partially vaccinated. The indirect protective effect of the first BNT162b2 vaccination campaign in Israel was evaluated between 22 December 2020 and 18 May 2021.

METHODS

The daily percentage of new polymerase chain reaction (PCR)-confirmed SARS-CoV-2 cases among unvaccinated individuals was analyzed for trends. Major shifts were identified using piecewise linear regression analysis. At these shifts, the percentage of naturally vaccinated (past SARS-CoV-2 cases) and the percentage of actively vaccinated (by inoculation) individuals were weighted and summed to determine the percentage of natural and active vaccination (NAV).

RESULTS

A first decline among unvaccinated individuals occurred during a lockdown period, when the percentage of NAV was 8.16%. The major decline occurred after the end of the lockdown when the percentage of NAV reached 52.05%. SARS-CoV-2 cases ultimately declined among unvaccinated individuals when the percentage of NAV reached 63.55%. During the study period, the Alpha variant was prevalent and the use of nonpharmaceutical interventions, including social distancing, existed to varying degrees.

CONCLUSIONS

The vaccination campaign played a major role in the decline of SARS-CoV-2 infection among unvaccinated individuals, leading to the end of the first 2021 SARS-CoV-2 wave (Alpha variant) in Israel. Infection in unvaccinated individuals stopped when two-thirds of the population were naturally or actively vaccinated. Any change in characteristics of the virus or the population can lead to a new outbreak.

Waning of Maternal Antibodies against Measles Suggests a Large Window of Susceptibility in Infants in Lao People's Democratic Republic

INTRODUCTION

Measles is an endemic but largely neglected disease in Lao People's Democratic Republic. New-borns are protected by maternal antibodies, but antibody waning before measles vaccination at 9 months of age leaves infants susceptible to infection. In this study, the susceptibility window of infants was determined to generate scientific evidence to assess the national measles immunization strategy.

METHODS

Between 2015 and 2016, demographic data, medical history, and blood samples were collected from 508 mother-child pairs at the provincial hospital in Vientiane. The samples were screened with a commercial kit detecting anti-measles IgG antibodies.

RESULTS

The large majority (95.7%) of the mothers were seropositive for anti-measles IgG and antibody titers of the mothers and infants were highly correlated (p < 0.01). While at birth 97.7% of the infants were seropositive, seropositivity rates decreased to 74.2% two months later to reach only 28.2% four months after birth (p < 0.01). Just before the first dose of the measles-rubella vaccine, scheduled at 9 months of age, was actually given, less than 14% of the infants were seropositive.

CONCLUSION

This alarmingly wide susceptibility gap due to rapid maternal antibody decay leaves infants at risk of measles infection and serious disease complications. A high herd immunity is crucial to protect young infants and can be achieved through improved routine vaccination coverage and (expanded age group) supplementary immunization activities.

Multiplexed VaxArray immunoassay for rapid antigen quantification in measles and rubella vaccine manufacturing

Measles-containing vaccines (MCV), specifically vaccines against measles and rubella (MR), are extremely effective and critical for the eradication of measles and rubella diseases. In developed countries, vaccination rates are high and vaccines are readily available, but continued high prevalence of both diseases in developing countries and surges in measles deaths in recent years have highlighted the need to expand vaccination efforts. To meet demand for additional vaccines at a globally affordable price, it is highly desirable to streamline vaccine production thereby reducing cost and speeding up time to delivery. MR vaccine characterization currently relies on the 50% cell culture infectious dose (CCID₅₀) assay, an endpoint assay with low reproducibility that requires 10–14 days to complete. For streamlining bioprocess analysis and improving measurement precision relative to CCID₅₀, we developed the VaxArray Measles and Rubella assay kit, which is based on a multiplexed microarray immunoassay with a 5-hour time to result. Here we demonstrate vaccine-relevant sensitivity ranging from 345 to 800 IFU/mL up to 100,000 IFU/mL (infectious units per mL) and specificity that allows simultaneous analysis in bivalent vaccine samples. The assay is sensitive to antigen stability and has minimal interference from common vaccine additives. The assay exhibits high reproducibility and repeatability, with 15% CV, much lower than the typical 0.3 log₁₀ error (∼65%) observed for the CCID₅₀ assay. The intact protein concentration measured by VaxArray is reasonably correlated to, but not equivalent to, CCID₅₀ infectivity measurements for harvest samples. However, the measured protein concentration exhibits equivalency to CCID₅₀ for more purified samples, including concentrated virus pools and monovalent bulks, making the assay a useful new tool for same-day analysis of vaccine samples for bioprocess development, optimization, and monitoring.

Measles outbreak in complex emergency: estimating vaccine effectiveness and evaluation of the vaccination campaign in Borno State, Nigeria, 2019

BACKGROUND

From January to May 2019, large measles outbreaks affected Nigeria. Borno state was the most affected, recording 15,237 suspected cases with the state capital of Maiduguri having 1125 cases investigated and line-listed by March 2019. In Borno state, 22 of the 27 Local Government Areas (LGAs or Districts), including 37 internally displaced persons (IDPs) camps were affected. In response to the situation, an outbreak response immunization (ORI) campaign was conducted in the 13 most affected LGAs. In addition to conventional vaccination teams, special teams were deployed in security compromised areas, areas with migrants, and for nomadic and IDPs. Here we describe the outbreak and the ORI campaign. We also assess the measles-containing vaccine (MCV) coverage and vaccine effectiveness (VE) in order to quantify the population-level impact.

METHODS

We reviewed the ORI activities, and conducted an analysis of the surveillance and the outbreak investigation reports. We assessed VE of MCV by applying the screening-method. Sensitivity analyses were also conducted to assess the effect of final classification of cases on the VE of MCV. The MCV coverage was assessed by a post-campaign coverage survey after completion of the ORI through a quantitative survey in the 12 LGAs that were accessible.

RESULTS

Of the total 15,237 reported measles cases, 2002 cases were line-listed and investigated, and 737 were confirmed for measles by week 9 of 2019. Of the investigated cases 67.3% (n = 1348) were between 9 and 59 months of age. Among the 737 confirmed cases, only 9% (n = 64) stated being vaccinated with at least 1 dose of MCV. The overall VE for MCV was 98.4% (95%CI: 97.8-98.8). No significant differences were observed in the VE estimates of lab-confirmed and epi-linked cases when compared to the original estimates. The aggregated weighted vaccination coverage was 85.7% (95% CI: 79.6-90.1).

CONCLUSION

The experience in Borno demonstrates that adequate VE can be obtained in conflict-affected areas. In complex emergencies affected by measles outbreaks, health authorities may consider integration with other health strategies and the engagement of security personnel as part of the ORI activities.

Observational study of a new strategy and management policy for measles prevention in medical personnel in a hospital setting

BACKGROUND

At the end of March 2018, a clustered outbreak of measles associated with health care workers occurred in northern Taiwan. Prior to this study, the policy for measles vaccination for physicians and nurses in MacKay Memorial Hospital, Taiwan was encouragement of vaccination in medical personnel working in the emergency room or other high risk divisions without prior testing for measles antibody, and vaccination coverage was only 85.3%. It was important to urgently formulate a new strategy to achieve zero tolerance for intra-hospital transmission and epidemic prevention. This study aimed to explore the effectiveness of a new strategy for the prevention of an outbreak of measles.

METHODS

This study was conducted from April 23, 2018 to May 22, 2018 in the MacKay Memorial Hospital, a medical center and tertiary teaching hospital with 2200 beds in northern Taiwan. First-line medical personnel in the hospital underwent a free screening for measles antibody as a new strategy for measles outbreak prevention. Susceptible medical personnel were advised to receive measles vaccination.

RESULTS

A total of 719 first-line medical personnel were enrolled for the general survey. Measles seropositivity was 76.1% (287/377) in the generation born after 1978 (vaccinated), and 96.5% (330/342) in the generation born before 1978 (p < 0.001), while the overall seropositivity was 85.8% (617/719). Vaccination coverage of susceptible personnel under the new strategy reached 86.3% in the first month (88/102) following the survey. At the end of the first month after implementation of the new strategy, 98.1% of the medical personnel were seropositive or revaccinated, and reached 99.4% at the end of the second month.

CONCLUSIONS

In this study, rapid, free antibody screening during a measles outbreak and subsequent vaccination of those susceptible resulted in most of the first-line medical personnel being seropositive or revaccinated. The new strategy was effective, time saving, used little manpower, and of low cost. Screening for measles antibody free of charge followed by vaccination of seronegative medical personnel can be regarded as an effective health management strategy to reduce and prevent the spread of measles infection.

Drivers of vaccine decision-making in South Africa: A discrete choice experiment

To increase vaccination coverage, it is essential to understand the vaccine decision-making process. High population coverage is required to obtain herd immunity and to protect vulnerable groups in terms of age (e.g. the very young) or health (e.g. immunodeficiency). Vaccine confidence and coverage in South Africa are relatively low, opening the window for sustained outbreaks of vaccine-preventable diseases in a country facing one of the most severe HIV epidemics in the world. To capture the vaccine-related decision-making process in South Africa, we performed a discrete choice experiment with 1200 participants in December 2017. We asked for their preferences with respect to (1) vaccine effectiveness, (2) vaccine-preventable burden of disease, (3) accessibility of the vaccine in terms of co-payment and prescription requirements, (4) frequency of mild vaccine-related side-effects, (5) population vaccination coverage and (6) local vaccination coverage. We distinguished between decision-making for vaccines administered to the participant, and for vaccines administered to their youngest child. We analyzed the data for each of these groups using a panel mixed logit model and found similar results for decisions to vaccinate oneself or one's child. Vaccine effectiveness was the most important attribute followed by population coverage and burden of disease. Local coverage and accessibility were also important determinants of vaccination behavior, but to a lesser extent. Regarding population and local coverage, we observed a positive effect on vaccine utility indicating the potential of peer influence. As such, social normative influence could be exploited to increase vaccination confidence and coverage. With respect to vaccine-preventable burden of the disease, the marginal utilities showed disease severity to be more important than frequency of disease. Policymakers and health care workers should stress the effectiveness of vaccines together with the severity of vaccine-preventable diseases.

Epidemiological characteristics and trends of a Nationwide measles outbreak in Mongolia, 2015-2016

Background

Mongolia was one of the four countries that received a measles-elimination certificate from the World Health Organization Regional Office for the Western Pacific in 2014. Following the outbreaks in many countries including China, a large measles outbreak occurred in Mongolia in 2015. This study reports 2015–2016 measles outbreak incidence, mortality, and complications, according to time, geographical distribution, and host characteristics.

Methods

The epidemiological characteristics and trends of measles outbreak were analyzed using the Mongolian national surveillance data reported to the Center for Health Development, Ministry of Health, from January 2015 to December 2016.

Results

In total, 23,464 cases of measles including eight deaths were reported in 2015, and 30,273 cases of measles including 132 deaths were reported in 2016, which peaked in June 2015 and March 2016, respectively. Majority of the cases were reported from Ulaanbaatar (35,397, 65.9%). The highest attack rates were 241 per 10,000 population in Darkhan-Uul aimag, and 263 per 10,000 population in Ulaanbaatar. Measles-related death, nosocomial infection, and complications were most frequent among children aged < 1 year.

Conclusions

Following no reports of measles since 2011, a large nationwide outbreak occurred in Mongolia, despite the high vaccination coverage in the past. The highest incidence rate was reported in Ulaanbaatar city, and Umnugovi aimag in 2015 and Darkhan-Uul aimag in 2016. The most affected age group were aged < 1 year and those aged 15–24 years. Mortality cases were prominent among children aged < 1 year who were not eligible for vaccination. A systematic vaccination strategy is required to prevent another measles outbreak.

Electronic supplementary material

The online version of this article (10.1186/s12889-019-6511-0) contains supplementary material, which is available to authorized users.

Imperfect vaccine and hysteresis

Addressing vaccine compliance problems is of particular relevance and significance to public health. Despite resurgence of vaccine-preventable diseases and public awareness of vaccine importance, why is it so challenging to boost population vaccination coverage to desired levels especially in the wake of declining vaccine uptake? To understand this puzzling phenomenon, here we study how social imitation dynamics of vaccination can be impacted by the presence of imperfect vaccine, which only confers partial protection against the disease. Besides weighing the perceived cost of vaccination with the risk of infection, the effectiveness of vaccination is also an important factor driving vaccination decisions. We discover that there can exist multiple stable vaccination equilibria if vaccine efficacy is below a certain threshold. Furthermore, our bifurcation analysis reveals the occurrence of hysteresis loops of vaccination rate with respect to changes in the perceived vaccination cost as well as in the vaccination effectiveness. Moreover, we find that hysteresis is more likely to arise in spatial populations than in well-mixed populations, even for parameter choices that do not allow for bifurcation in the latter. Our work shows that hysteresis can appear as an unprecedented roadblock for the recovery of vaccination uptake, thereby helping explain the persistence of vaccine compliance problem.

Assessment of vaccine effectiveness during measles outbreak in the Federation of Bosnia and Herzegovina, 2014-2015

OBJECTIVE

Between February 2014 and September 2015 a large measles outbreak (5,084 cases) occurred in the Federation of Bosnia and Herzegovina (FB&H). The aim of this study is to assess the effectiveness of routine measles vaccination in the FB&H.

METHODS

We conducted an analysis of the resurgence period surveillance data and a retrospective cohort study involving primary school aged children in randomly selected schools.

RESULTS

Measles cases occurred among all age groups, mostly among the unvaccinated. Among fully immunized, 2.1% contracted measles. Measles vaccine effectiveness was high. The study indicates that one dose reduced the risk for measles by 91.9% (95% CI: 81.4-96.4%), two doses reduced the risk by 97.3% (95% CI: 95.5-98.4%). No evidence of waning immunity was found. Our survey reveals that a significant number of children had no immunization status registered.

CONCLUSIONS

The results of this study suggest that the resurgence was likely caused by an accumulation of measles-susceptible children not being vaccinated. This vaccine effectiveness study does not support possible vaccination failure as a contributing factor.

Measles outbreak propagated by children congregating at water collection points in Mayuge District, eastern Uganda, July - October, 2016

BACKGROUND

On 12 October, 2016 a measles outbreak was reported in Mayuge District, eastern Uganda. We investigated the outbreak to determine its scope, identify risk factors for transmission, evaluate vaccination coverage and vaccine effectiveness, and recommend evidence-based control measures.

METHODS

We defined a probable case as onset of fever (≥3 days) and generalized rash, plus ≥1 of the following: conjunctivitis, cough, and/or runny nose in a Mayuge District resident. A confirmed case was a probable case with measles-specific IgM (+) not explained by vaccination. We reviewed medical records and conducted active community case-finding. In a case-control investigation involving probable case-persons and controls matched by age and village, we evaluated risk factors for transmission for both cases and controls during the case-person's likely exposure period (i.e., 7-21 days prior to rash onset). We estimated vaccine effectiveness (VE) using the formula: VE ≈ (1-ORprotective) × 100. We calculated vaccination coverage using the percentage of controls vaccinated.

RESULTS

We identified 62 probable case-persons (attack rate [AR] = 4.0/10,000), including 3 confirmed. Of all age groups, children < 5 years were the most affected (AR = 14/10,000). The epidemic curve showed a propagated outbreak. Thirty-two percent (13/41) of case-persons and 13% (21/161) of control-persons visited water-collection sites (by themselves or with parents) during the case-persons' likely exposure period (ORM-H = 5.0; 95% CI = 1.5-17). Among children aged 9-59 months, the effectiveness of the single-dose measles vaccine was 75% (95% CI = 25-92); vaccination coverage was 68% (95% CI = 61-76).

CONCLUSIONS

Low vaccine effectiveness, inadequate vaccination coverage and congregation at water collection points facilitated measles transmission in this outbreak. We recommended increasing measles vaccination coverage and restriction of children with signs and symptoms of measles from accessing public gatherings.

Epidemiological and molecular investigation of a measles outbreak in Punjab, Pakistan, 2013-2015

Despite the availability of an effective vaccine, the measles virus continues to cause significant morbidity and mortality in children worldwide. Molecular characterization of wild-type measles strains is an invaluable component of epidemiological studies or surveillance systems that provides important information pertinent to outbreak linkages and transmission pathways. Serum samples and throat swabs were collected from suspected measles cases from the Punjab province of Pakistan (2013-2015) and further tested for measles immunoglobulin M (IgM) through enzyme-linked immunosorbent assay and reverse-transcriptase polymerase chain reaction for molecular characterization. Among the total of 5415 blood samples, 59% tested positive for measles IgM. Males had a higher infection rate (55%) than females (45%), and the highest frequency of positive cases (63%) was found in the age group of 0 to 5 years. Partial sequencing of the nucleoprotein gene showed that 27 strains belonged to the B3 genotype, whereas 2 viruses were identified as D4. On phylogenetic analysis, Pakistani B3 strains were found to be closely related to previously reported indigenous strains and those from neighboring countries of Iran and Qatar. This is the first report on the detection of the measles B3 genotype from Punjab, Pakistan. The current study shows a high burden of measles infections in Punjab province owing to poor routine immunization coverage in major cities. It is imperative that national health authorities adopt strategic steps on an urgent basis for improvement of routine immunization coverage. Molecular epidemiology of the measles viruses circulating in different parts of the country can provide useful data to manage future outbreaks.

Role of health determinants in a measles outbreak in Ecuador: a case-control study with aggregated data

BACKGROUND

In 2011-2012, an outbreak of measles occurred in Ecuador. This study sought to ascertain which population characteristics were associated.

METHODS

Case-control study of aggregate data. The unit of analysis was the parish (smallest geographic division). The national communicable disease surveillance database was used to identify 52 case parishes (with at least one confirmed case of measles) and 972 control parishes (no cases of measles). A hierarchical model was used to determine the association of measles with population characteristics and access to health care.

RESULTS

Case parishes were mostly urban and had a higher proportion of children under 1 year of age, heads of household with higher educational attainment, larger indigenous population, lower rates of measles immunization, and lower rates of antenatal care visit attendance. On multivariate analysis, associations were found with educational attainment of head of household ≥8 years (OR: 0.29; 95%CI 0.15-0.57) and ≥1.4% indigenous population (OR: 3.29; 95%CI 1.63-6.68). Antenatal care visit attendance had a protective effect against measles (OR: 0.98; 95%CI 0.97-0.99). Measles vaccination was protective of the outbreak (OR: 0.97; 95%CI 0.95-0.98). The magnitude of these associations was modest, but represents the effect of single protective factors, capable of acting at the population level regardless of socioeconomic, biological, and environmental confounding factors.

CONCLUSION

In Ecuador, the parishes with the highest percentage of indigenous populations and those with the lowest vaccination coverage were the most vulnerable during the measles outbreak.

Local measles vaccination gaps in Germany and the role of vaccination providers

Background

Measles elimination in Europe is an urgent public health goal, yet despite the efforts of its member states, vaccination gaps and outbreaks occur. This study explores local vaccination heterogeneity in kindergartens and municipalities of a German county.

Methods

Data on children from mandatory school enrolment examinations in 2014/15 in Reutlingen county were used. Children with unknown vaccination status were either removed from the analysis (best case) or assumed to be unvaccinated (worst case). Vaccination data were translated into expected outbreak probabilities. Physicians and kindergartens with statistically outstanding numbers of under-vaccinated children were identified.

Results

A total of 170 (7.1%) of 2388 children did not provide a vaccination certificate; 88.3% (worst case) or 95.1% (best case) were vaccinated at least once against measles. Based on the worst case vaccination coverage, <10% of municipalities and <20% of kindergartens were sufficiently vaccinated to be protected against outbreaks. Excluding children without a vaccination certificate (best case) leads to over-optimistic views: the overall outbreak probability in case of a measles introduction lies between 39.5% (best case) and 73.0% (worst case). Four paediatricians were identified who accounted for 41 of 109 unvaccinated children and for 47 of 138 incomplete vaccinations; GPs showed significantly higher rates of missing vaccination certificates and unvaccinated or under-vaccinated children than paediatricians.

Conclusions

Missing vaccination certificates pose a severe problem regarding the interpretability of vaccination data. Although the coverage for at least one measles vaccination is higher in the studied county than in most South German counties and higher than the European average, many severe and potentially dangerous vaccination gaps occur locally. If other federal German states and EU countries show similar vaccination variability, measles elimination may not succeed in Europe.

Electronic supplementary material

The online version of this article (doi:10.1186/s12889-017-4663-3) contains supplementary material, which is available to authorized users.

Measles Outbreak with Unique Virus Genotyping, Ontario, Canada, 2015

The province of Ontario continues to experience measles virus transmissions despite the elimination of measles in Canada. We describe an unusual outbreak of measles in Ontario, Canada, in early 2015 that involved cases with a unique strain of virus and no known association among primary case-patients. A total of 18 cases of measles were reported from 4 public health units during the outbreak period (January 25-March 23, 2015); none of these cases occurred in persons who had recently traveled. Despite enhancements to case-patient interview methods and epidemiologic analyses, a source patient was not identified. However, the molecular epidemiologic analysis, which included extended sequencing, strongly suggested that all cases derived from a single importation of measles virus genotype D4. The use of timely genotype sequencing, rigorous epidemiologic investigation, and a better understanding of the gaps in surveillance are needed to maintain Ontario's measles elimination status.

Complete Genome Sequence of a Wild-Type Measles Virus Isolated during a 2016 Winter Outbreak in a Refugee Settlement in Calais, France

Measles outbreaks are regularly reported in European countries despite efforts to improve vaccination coverage. In January 2016, an outbreak occurred in a refugee settlement in Calais, France. We report here the complete genome sequence of a wild-type measles virus isolated from a health care worker (MVi/Calais. FRA/01.16) infected during this outbreak.

A review of measles supplementary immunization activities and the implications for Pacific Island countries and territories

INTRODUCTION

Standard measles control strategies include achieving high levels of measles vaccine coverage using routine delivery systems, supplemented by mass immunization campaigns as needed to close population immunity gaps. Areas covered: This review looks at how supplementary immunization activities (SIAs) have contributed to measles control globally, and asks whether such a strategy has a place in Pacific Islands today. Expert commentary: Very high coverage with two doses of measles vaccine seems to be the optimal strategy for controlling measles. By 2015, all but two Pacific Islands had introduced a second dose in the routine schedule; however, a number of countries have not yet reached high coverage with their second dose. The literature and the country reviews reported here suggest that a high coverage SIA combined with one dose of measles vaccine given in the routine system will also do the job. The arguments for and against the use of SIAs are complex, but it is clear that to be effective, SIAs need to be well designed to meet specific needs, must be carried out effectively and safely with very high coverage, and should, when possible, carry with them other public health interventions to make them even more cost-effective.

Genetically defined race, but not sex, is associated with higher humoral and cellular immune responses to measles vaccination

In addition to host genetic and environmental factors, variations in immune responses to vaccination are influenced by demographic variables, such as race and sex. The influence of genetic race and sex on measles vaccine responses is not well understood, yet important for the development of much-needed improved measles vaccines with lower failure rates. We assessed associations between genetically defined race and sex with measles humoral and cellular immunity after measles vaccination in three independent and geographically distinct cohorts totaling 2872 healthy racially diverse children, older adolescents, and young adults. We found no associations between biological sex and either humoral or cellular immunity to measles vaccine, and no correlation between humoral and cellular immunity in these study subjects. Genetically defined race was, however, significantly associated with both measles vaccine-induced humoral and cellular immune responses, with subjects genetically classified as having African-American ancestry demonstrating significantly higher antibody and cell-mediated immune responses relative to subjects of Caucasian ancestry. This information may be useful in designing novel measles vaccines that are optimally effective across human genetic backgrounds.

Factors affecting the seroconversion rate of 12-month-old babies after the first injection of measles vaccine in the southeast of Iran

Within the past few years, several measles outbreaks have occurred in the southeast of Iran. To learn about the effectiveness of the immunization services for producing a serologic response against measles, this follow-up study was designed and implemented in the southeast of Iran. In Iran, all routine immunization services provided by the public sector are free of charge. The follow-up study was designed and implemented in 5 Urban Health Centers located in 3 districts of Sistan-va-BaluchestanProvince, Iran. In the pre-vaccination phase, 270 12-month-old babies were blood sampled; and in the post-vaccination phase, 4 to 7 weeks after Measles, Mumps, Rubella (MMR) vaccination, 236 of them were blood sampled (34 dropouts), and their sera were tested for IgG anti-measles antibodies, using indirect ELISA, in the National Reference Measles Laboratory. Out of the 236 participants, who had been blood sampled in the post-vaccination phase, 10 (3.7%) were excluded from the calculations of seroconversion rate, because they had protective levels of antibody before the vaccination. The seroconversion rate for the remaining 226 participants was 91.2% (95% confidence interval: 86.7 to 94.5). Among the variables studied, stunting (height-for-age z-score < -2) showed a strong relationship with the remaining seronegative after the vaccination (odds ratio = 5.6; 95% confidence interval: 1.7-18.2). The chance of seroconversion was inversely related to the mothers' levels of education (up to 9 y of education vs. above nine years) (odds ratio = 0.2; 95% confidence interval: 0.06-0.4). In the study population, the seroconversion rates for anti-measles antibodies after MMR vaccination are acceptable, even though in order to achieve the elimination goal, higher standards need to be achieved.

Measles Elimination Activities in the Western Pacific Region: Experience from the Republic of Korea

We describe the global status of measles control and elimination, including surveillance and vaccination coverage data provided by the World Health Organization (WHO). Since 2000, two doses of measles vaccine (MCV2) became recommended globally and the achievement of high vaccination coverage has led to dramatic decrease in the measles incidence. Our finding indicates that, in the Western Pacific Region (WPR), substantial progress has been made to control measles transmission in some countries; however, the measles virus continues to circulate, causing outbreaks. The Republic of Korea (ROK) experienced a series of resurgence of measles due to the importation and healthcare-associated transmission in infants, however overall incidence and surveillance indicators met the WHO criteria for measles elimination. The ROK was verified to be measles-free along with Australia, Mongolia, and Macau, China in 2014. One of the effective elimination activities was the establishment of solid keep-up vaccination system in school settings. The lessons learnt from the measles elimination activities in Korea may contribute to enhancing the surveillance schemes and strengthening of vaccination programs in member countries and areas of WPR.

MMR vaccination status of children exempted from school-entry immunization mandates

BACKGROUND

Child immunizations are one of the most successful public health interventions of the past century. Still, parental vaccine hesitancy is widespread and increasing. One manifestation of this are rising rates of nonmedical or "personal beliefs" exemptions (PBEs) from school-entry immunization mandates. Exemptions have been shown to be associated with increased risk of disease outbreak, but the strength of this association depends critically on the true vaccination status of exempted children, which has not been assessed.

OBJECTIVE

To estimate the true measles-mumps-rubella (MMR) vaccination status of children with PBEs.

METHODS

We use administrative data collected by the California Department of Public Health in 2009 and imputation to estimate the MMR vaccination status of children with PBEs under varying scenarios.

RESULTS

Results from 2009 surveillance data indicate MMR1/MMR2 coverage of 18-47% among children with PBEs at typical schools and 11-34% among children with PBEs at schools with high PBE rates. Imputation scenarios point to much higher coverage (64-92% for MMR1 and 25-58% for MMR2 at typical schools; 49-90% for MMR1 and 16-63% for MMR2 at high PBE schools) but still below levels needed to maintain herd immunity against measles.

CONCLUSIONS

These coverage estimates suggest that prior analyses of the relative risk of measles associated with vaccine refusal underestimate that risk by an order of magnitude of 2-10 times.

Improved coverage and timing of childhood vaccinations in two post-Soviet countries, Armenia and Kyrgyzstan

BACKGROUND

Timing of childhood vaccinations has received close attention in many countries. Little is known about the trends in correctly timed vaccination in former Soviet countries. We examined trends in vaccination coverage and correct timing of vaccination in two post-Soviet countries, Armenia and Kyrgyzstan, and analyzed factors associated with delayed vaccinations.

METHODS

We used data from the Demographic and Health Surveys; the surveys were conducted in 2000 (n = 1726), 2005 (n = 1430) and 2010 (n = 1473) in Armenia and in 1997 (n = 1127) and 2012 (n = 4363) in Kyrgyzstan. We applied the Kaplan-Meier method to estimate age-specific vaccination coverage with diphtheria, tetanus and pertussis (DTP) vaccine and a measles-containing vaccine (MCV). A Cox proportional hazard regression with shared frailty was used to examine factors associated with delayed vaccinations.

RESULTS

Vaccination coverage for all three doses of the DTP vaccine increased in Armenia from 92 % in 2000 to 96 % in 2010. In Kyrgyzstan, DTP coverage was 96 % and 97 % in 1997 and 2012, respectively. Vaccination coverage for MCV increased from 89 % (Armenia, 2000) and 93 % (Kyrgyzstan, 1997) to 97 % (Armenia, 2010) and 98 % (Kyrgyzstan, 2012). The proportion of children with correctly timed vaccinations increased over time for all examined vaccinations in both countries. For example, the proportion of children in Armenia with correctly timed first DTP dose (DTP1) increased from 46 % (2000) to 66 % (2010). In Kyrgyzstan, the proportion of correctly timed DTP1 increased from 75 % (1997) to 87 % (2012). In Armenia, delays in the third DTP dose (DTP3) and MCV vaccinations were less likely to occur in the capital, whereas in Kyrgyzstan DTP3 and MCV start was delayed in the capital compared to other regions of the country. Also, in Armenia living in urban areas was associated with delayed vaccinations.

CONCLUSIONS

Vaccination coverage and timing of vaccination improved over the last years in both countries. Further efforts are needed to reduce regional differences in timely vaccinations.

Vaccinations in prisons: A shot in the arm for community health

From the first day of imprisonment, prisoners are exposed to and expose other prisoners to various communicable diseases, many of which are vaccine-preventable. The risk of acquiring these diseases during the prison sentence exceeds that of the general population. This excess risk may be explained by various causes; some due to the structural and logistical problems of prisons and others to habitual or acquired behaviors during imprisonment. Prison is, for many inmates, an opportunity to access health care, and is therefore an ideal opportunity to update adult vaccination schedules. The traditional idea that prisons are intended to ensure public safety should be complemented by the contribution they can make in improving community health, providing a more comprehensive vision of safety that includes public health.

A microneedle patch containing measles vaccine is immunogenic in non-human primates

Very high vaccination coverage is required to eliminate measles, but achieving high coverage can be constrained by the logistical challenges associated with subcutaneous injection. To simplify the logistics of vaccine delivery, a patch containing micron-scale polymeric needles was formulated to encapsulate the standard dose of measles vaccine (1000 TCID₅₀) and the immunogenicity of the microneedle patch was compared with subcutaneous injection in rhesus macaques. The microneedle patch was administered without reconstitution with diluent, dissolved in skin within 10 min, and caused only mild, transient skin erythema. Both groups of rhesus macaques generated neutralizing antibody responses to measles that were consistent with protection and the neutralizing antibody titers were equivalent. In addition, the microneedle patches maintained an acceptable level of potency after storage at elevated temperature suggesting improved thermostability compared to standard lyophilized vaccine. In conclusion, a measles microneedle patch vaccine was immunogenic in non-human primates, and this approach offers a promising delivery method that could help increase vaccination coverage.

Measles surveillance in Canada: Trends for 2013

OBJECTIVE

The objective of this report is to describe measles activity in Canada during 2013, in order to support the documentation and maintenance of measles elimination status.

METHODS

A descriptive analysis of measles counts and incidence by age group, immunization history, hospitalization and province/territory, as well as a summary of 2013 outbreaks, was conducted using enhanced measles data captured through the Canadian Measles and Rubella Surveillance System. Genotype information and phylogenetic analysis for 2013 were summarized.

RESULTS

In 2013, 83 confirmed measles cases were reported in seven provinces/territories for an incidence rate of 2.4 per 1,000,000 population. Incidence was highest in the youngest age groups (< 1 year, 1 to 4 years). Burden of disease was highest in the youngest age groups and children 10 to 14 years. Three-quarters of cases had been inadequately immunized, and 10% were hospitalized. There were nine measles outbreaks reported in 2013, one of which consisted of 42 cases in a non-immunizing community in Alberta.

DISCUSSION

2013 saw the fifth highest number of reported measles cases since 1998. While we continue to face challenges related to importation and heterogeneous immunization coverage, in 2013 Canada met or partially met all four criteria outlined by the Pan American Health Organization for measles elimination.

Adult patients hospitalized for measles in France, in the 21st century

BACKGROUND

An epidemic of measles broke out in France in 2008. We designed a retrospective study focusing on adults hospitalized for measles in 2010/2011.

METHODS

A case was any patient aged more than 15 years, hospitalized (September 2010 to September 2011) with a typical rash or a biological diagnosis. Data was collected with standardized questionnaires in participating hospitals.

RESULTS

Four hundred and sixty cases were reported: sex-ratio (M/F) = 0.93, median age 26 years (σ = 8.8). Twenty-nine cases were severe (6.5%), 27 of which hospitalized in an ICU. Three hundred and twelve (68%) cases had elevated serum transaminases (EST), 155 (34%) cases had pneumonia, 34 (7%) cases had elevated serum creatinine (ESC), four (0.9%) cases had elevated serum amylase and lipase (ESAL), and three (0.7%) cases had neurological symptoms. One hundred and four (23%) patients presented simultaneously with EST and pneumonia. One patient presenting with severe pneumonia died (0.2%). One hundred and ten (24%) patients received antibiotics during a median seven days.

CONCLUSION

Measles can present as various syndromes in adults and be responsible for a high burden during outbreaks. The immediate outcome is favorable in most patients. Long-term outcome needs further investigations to identify possible late complications.

Estimation of vaccine efficacy and critical vaccination coverage in partially observed outbreaks

Classical approaches to estimate vaccine efficacy are based on the assumption that a person's risk of infection does not depend on the infection status of others. This assumption is untenable for infectious disease data where such dependencies abound. We present a novel approach to estimating vaccine efficacy in a Bayesian framework using disease transmission models. The methodology is applied to outbreaks of mumps in primary schools in the Netherlands. The total study population consisted of 2,493 children in ten primary schools, of which 510 (20%) were known to have been infected, and 832 (33%) had unknown infection status. The apparent vaccination coverage ranged from 12% to 93%, and the apparent infection attack rate varied from 1% to 76%. Our analyses show that vaccination reduces the probability of infection per contact substantially but not perfectly ([Formula: see text] = 0.933; 95CrI: 0.908-0.954). Mumps virus appears to be moderately transmissible in the school setting, with each case yielding an estimated 2.5 secondary cases in an unvaccinated population ([Formula: see text] = 2.49; 95%CrI: 2.36-2.63), resulting in moderate estimates of the critical vaccination coverage (64.2%; 95%CrI: 61.7-66.7%). The indirect benefits of vaccination are highest in populations with vaccination coverage just below the critical vaccination coverage. In these populations, it is estimated that almost two infections can be prevented per vaccination. We discuss the implications for the optimal control of mumps in heterogeneously vaccinated populations.

Identifying high-risk areas for sporadic measles outbreaks: lessons from South Africa

OBJECTIVE

To develop a model for identifying areas at high risk for sporadic measles outbreaks based on an analysis of factors associated with a national outbreak in South Africa between 2009 and 2011.

METHODS

Data on cases occurring before and during the national outbreak were obtained from the South African measles surveillance programme, and data on measles immunization and population size, from the District Health Information System. A Bayesian hierarchical Poisson model was used to investigate the association between the risk of measles in infants in a district and first-dose vaccination coverage, population density, background prevalence of human immunodeficiency virus (HIV) infection and expected failure of seroconversion. Model projections were used to identify emerging high-risk areas in 2012.

FINDINGS

A clear spatial pattern of high-risk areas was noted, with many interconnected (i.e. neighbouring) areas. An increased risk of measles outbreak was significantly associated with both the preceding build-up of a susceptible population and population density. The risk was also elevated when more than 20% of infants in a populous area had missed a first vaccine dose. The model was able to identify areas at high risk of experiencing a measles outbreak in 2012 and where additional preventive measures could be undertaken.

CONCLUSION

The South African measles outbreak was associated with the build-up of a susceptible population (owing to poor vaccine coverage), high prevalence of HIV infection and high population density. The predictive model developed could be applied to other settings susceptible to sporadic outbreaks of measles and other vaccine-preventable diseases.

Effectiveness and timing of vaccination during school measles outbreak

Implementing a vaccination campaign during an outbreak can effectively reduce the outbreak size.

Exposure of California kindergartners to students with personal belief exemptions from mandated school entry vaccinations

OBJECTIVES

Personal belief exemptions (PBEs) from mandated school entry vaccinations have increased in California over the past decade. Infectious disease outbreaks in the state may be associated with the aggregation of intentionally unvaccinated children within schools. We sought to quantify the exposure of California kindergartners to children with PBEs at school.

METHODS

We used cross-sectional California Department of Public Health data on 3 kindergarten cohorts to define and calculate multiple measures of exposure to children with exemptions, including interaction and aggregation indices, for the state as a whole (2008-2010) and by county (2010).

RESULTS

In 2010, the PBE rate in California was 2.3 per 100 students, and the school PBE rate for the average kindergartner with a PBE was 15.6 per 100. More than 7000 kindergartners in California attend schools with PBE rates greater than 20 per 100, including 2700 kindergartners with PBEs. Exposure measures vary considerably across counties.

CONCLUSIONS

Our results suggest increasing levels of exposure among kindergarten students in California to other kindergartners with PBEs. Our data provide a concrete set of metrics through which public health and education officials can identify high-risk areas as targets for policy and programmatic interventions.

Higher risk of measles when the first dose of a 2-dose schedule of measles vaccine is given at 12-14 months versus 15 months of age

BACKGROUND

In 2011, >750 cases of measles were reported in Quebec, Canada, where a routine 2-dose measles immunization schedule, in which measles vaccine is given at 12 and 18 months of age, had been in effect since 1996. Effectiveness of this schedule was assessed during a high school outbreak.

METHODS

Cases were identified by passive followed by active surveillance. Classical cases met the national surveillance definition; attenuated cases showed clinical signs and high measles-specific immunoglobulin G but did not fulfill all classical criteria. Immunization status was ascertained from written records, and vaccine effectiveness (VE) was calculated as 1 - [(risk of measles in vaccinated individuals)/(risk in unvaccinated individuals)] × 100%.

RESULTS

Among 1306 students, 110 measles cases were identified; 98 were classical cases, and 12 were attenuated cases. The attack rates among unvaccinated and fully vaccinated students were 82% and 4.8%, respectively. The VE among 2-dose recipients was 95.5% against classical and 94.2% against all (classical + attenuated) measles. Among 2-dose recipients, attack rates with first immunization at 12 and ≥15 months of age were 5.8% and 2.0%, respectively, with corresponding VE values of 93.0% and 97.5%. The risk of measles in 2-dose recipients was significantly (3-4-fold) higher when vaccine was first administered at 12 months of age, compared with ≥15 months of age (P = .04).

CONCLUSIONS

Despite compliance with the recommended 2-dose measles immunization schedule, 6% of high school students were susceptible during this outbreak. Residual susceptibility was 2-4-fold higher among 2-dose recipients who had received the first dose of vaccine prior to 15 months of age. If confirmed in other settings, these results suggest that administration of the first dose of measles vaccine before 15 months of age may not be optimal for measles elimination efforts.

Real-time investigation of measles epidemics with estimate of vaccine efficacy

As part of measles elimination effort, evaluation of the vaccination program and real-time assessment of the epidemic dynamics constitute two important tasks to improve and strengthen the control. The present study aimed to develop an epidemiological modeling method which can be applied to estimating the vaccine efficacy at an individual level while conducting the timely investigation of the epidemic. The multivariate renewal process model was employed to describe the temporal evolution of infection by vaccination history, jointly estimating the time-dependent reproduction number and the vaccine efficacy. Analyzing the enhanced surveillance data of measles in Aichi prefecture, Japan from 2007-08, the vaccine efficacy was estimated at 96.7% (95% confidence interval: 95.8, 97.4). Using an age structured model, the vaccine efficacy among those aged from 5-19 years was shown to be smaller than that among those from 0-4 years. The age-dependent vaccine efficacy estimate informs the age-groups to be targeted for revaccination. Because the estimation method can rest on readily available epidemiological data, the proposed model has a potential to be integrated with routine surveillance.

Why we should eliminate personal belief exemptions to vaccine mandates

We argue that personal belief exemptions to the mandate for childhood immunizations should not be allowed. Parents who choose not to immunize their children put both their own children and other children at risk. Other children are at risk because unimmunized children go to school or day care when they are contagious but asymptomatic, exposing many more children to potentially dangerous infections. The risks to children from disease are much higher than the risks of vaccines. There are, of course, some bona fide reasons why children should not be immunized. Some children have known allergies or other medical contraindications to certain immunizations. Immunization refusals based on parental beliefs, however, do not fall into this category. In those cases, children are denied the protection of immunizations without any medical or scientific justification. By eliminating personal belief exemptions to those childhood vaccines associated with contagious diseases that have high rates of childhood mortality, we would better protect children and would more fairly spread the burdens of this important public health program.

Incidence and reproduction numbers of pertussis: estimates from serological and social contact data in five European countries

BACKGROUND

Despite large-scale vaccination programmes, pertussis has remained endemic in all European countries and has been on the rise in many countries in the last decade. One of the reasons that have been discussed for the failure of vaccination to eliminate the disease is continued circulation of the pathogen Bordetella pertussis by mostly asymptomatic and mild infections in adolescents and adults. To understand the impact of asymptomatic and undiagnosed infection on the transmission dynamics of pertussis we analysed serological data from five European countries in combination with information about social contact patterns from five of those countries to estimate incidence and reproduction numbers.

METHODS AND FINDINGS

We compared two different methods for estimating incidence from individual data on IgG pertussis toxin (PT) titres. One method combines the cross-sectional surveys of titres with longitudinal information about the distribution of amplitude and decay rate of titres in a back-calculation approach. The second method uses age-dependent contact matrices and cross-sectional surveys of IgG PT titres to estimate a next generation matrix for pertussis transmission among age groups. The next generation approach allows for computation of basic reproduction numbers for five European countries. Our main findings are that the seroincidence of infections as estimated with the first method in all countries lies between 1% and 6% per annum with a peak in the adolescent age groups and a second lower peak in young adults. The incidence of infections as estimated by the second method lies slightly lower with ranges between 1% and 4% per annum. There is a remarkably good agreement of the results obtained with the two methods. The basic reproduction numbers are similar across countries at around 5.5.

CONCLUSIONS

Vaccination with currently used vaccines cannot prevent continued circulation and reinfection with pertussis, but has shifted the bulk of infections to adolescents and adults. If a vaccine conferring lifelong protection against clinical and subclinical infection were available pertussis could be eliminated. Currently, continuing circulation of the pathogen at a subclinical level provides a refuge for the pathogen in which it can evolve and adjust to infect vaccinated populations. Please see later in the article for the Editors' Summary.