Assessment of pre-specified adverse events following varicella vaccine: A population-based self-controlled risk interval study.

BACKGROUND: Clinical trials and spontaneous reporting systems have revealed rare but biologically plausible adverse events following varicella immunization. Few post-marketing controlled studies have been conducted to assess the relationship between the varicella vaccine and these outcomes. OBJECTIVES: To evaluate the risk of pneumonia, idiopathic thrombocytopenic purpura (ITP), meningitis, encephalitis and ischemic stroke following varicella immunization. MATERIALS AND METHODS: This nationwide observational study was based on Taiwan National Health Insurance data and National Immunization Information System from 2004 through 2014. Primary analysis included children aged 12-35 months who received the single varicella vaccine on the date of administration. The self-controlled risk interval design compared the incidence of pre-specified outcomes during a risk interval of 1-42 days post-vaccination and a control interval of 43-84 days. The outcomes of interest were defined as admitted pneumonia, ITP, meningitis, encephalitis, and ischemic stroke, as well as fracture as a negative control. Conditional Poisson regression was used to assess the incidence rate ratio (aIRR) with adjustments for age and seasonal effects. RESULTS: Among 1,194,189 children, who receiving the varicella vaccine, there was no observed increase in the risk for ITP (aIRR 1.00; 95% CI, 0.76-1.33), meningitis (aIRR 1.21; 95% CI, 0.49-2.95), encephalitis (aIRR 1.00; 95% CI, 0.62-1.60), or ischemic stroke (aIRR 1.24; 95% CI, 0.31-4.95). A clustering feature with pneumonia occurred during days 36-42 post-vaccination (aIRR 1.10; 95% CI, 1.02-1.18). An increase in the risk for ITP was observed in children receiving the varicella and MMR vaccines concomitantly (aIRR 1.70; 95% CI, 1.19-2.43), but not among those receiving the varicella vaccine only. CONCLUSIONS: We detected a small risk of incidental pneumonia associated with varicella vaccine in the 6th week after immunization. There was no increase in the risk of other pre-specified adverse events.

Challenges in conducting post-authorisation safety studies (PASS): A vaccine manufacturer's view.

Post-authorisation safety studies (PASS) of vaccines assess or quantify the risk of adverse events following immunisation that were not identified or could not be estimated pre-licensure. The aim of this perspective paper is to describe the authors' experience in the design and conduct of twelve PASS that contributed to the evaluation of the benefit-risk of vaccines in real-world settings. We describe challenges and learnings from selected PASS of rotavirus, malaria, influenza, human papillomavirus and measles-mumps-rubella-varicella vaccines that assessed or identified potential or theoretical risks, which may lead to changes to risk management plans and/or to label updates. Study settings include the use of large healthcare databases and de novo data collection. PASS methodology is influenced by the background incidence of the outcome of interest, vaccine uptake, availability and quality of data sources, identification of the at-risk population and of suitable comparators, availability of validated case definitions, and the frequent need for case ascertainment in large databases. Challenges include the requirement for valid exposure and outcome data, identification of, and access to, adequate data sources, and mitigating limitations including bias and confounding. Assessing feasibility is becoming a key step to confirm that study objectives can be met in a timely manner. PASS provide critical information for regulators, public health agencies, vaccine manufacturers and ultimately, individuals. Collaborative approaches and synergistic efforts between vaccine manufacturers and key stakeholders, such as regulatory and public health agencies, are needed to facilitate access to data, and to drive optimal study design and implementation, with the aim of generating robust evidence.

Vaccine adverse events in a safety net healthcare system and a managed care organization.

BACKGROUND: The Institute of Medicine, in a 2013 report, recommended that the Vaccine Safety Datalink (VSD) expand collaborations to include more diversity in the study population. Kaiser Permanente Colorado (KPCO), an established VSD site, partnered with Denver Health (DH), an integrated safety net healthcare system, to demonstrate the feasibility of integrating DH data within the VSD. Prior to incorporating the data, we examined the identification of specific vaccine associated adverse events (VAEs) in these two distinct healthcare systems. METHODS: We conducted retrospective cohort analyses within KPCO and DH to compare select VAEs between the two populations. We examined the following associations between January 1, 2004 and December 31, 2013: Measles, Mumps, and Rubella (MMR) vaccine and febrile seizures in children 2years and younger, intussusception after rotavirus vaccine in infants 4-34weeks, syncope after adolescent vaccines (Tetanus, Diphtheria, acellular Pertussis; Meningococcal and Human Papillomavirus) in adolescents 13-17years and medically attended local reactions after pneumococcal polysaccharide (PPSV23) vaccine in adults 65years and older. Both sites used similar data procurement methods and chart review processes. RESULTS: For seizures after MMR vaccine (KPCO - 3.15vs. DH - 2.97/10,000 doses) and syncope after all adolescent vaccines (KPCO - 3.0vs. DH - 2.37/10,000 doses), the chart confirmed rates were comparable at the two sites. However, for medically attended local reactions after PPSV23, there were differences in chart confirmed rates between the sites (KPCO - 31.65vs. DH - 14.90/10,000 doses). For intussusception after rotavirus vaccine, the number of cases was too low to make a valid comparison (KPCO - 0vs. DH - 0.13/10,000 doses). CONCLUSION: We demonstrated that data on important targeted VAEs can be captured at DH and rates appear similar to those at KPCO. Work is ongoing on the optimal approach to assimilate DH data as a potential safety net healthcare system in the VSD.

A model to estimate the impact of changes in MMR vaccine uptake on inequalities in measles susceptibility in Scotland.

An article published in 1998 by Andrew Wakefield in The Lancet (volume 351, pages 637-641) led to concerns surrounding the safety of the measles, mumps and rubella vaccine, by associating it with an increased risk of autism. The paper was later retracted after multiple epidemiological studies failed to find any association, but a substantial decrease in UK vaccination rates was observed in the years following publication. This paper proposes a novel spatio-temporal Bayesian hierarchical model with accompanying software (the R package CARBayesST) to simultaneously address three key epidemiological questions about vaccination rates: (i) what impact did the controversy have on the overall temporal trend in vaccination rates in Scotland; (ii) did the magnitude of the spatial inequality in measles susceptibility in Scotland increase due to the measles, mumps and rubella vaccination scare; and (iii) are there any covariate effects, such as deprivation, that impacted on measles susceptibility in Scotland. The efficacy of the model is tested by simulation, before being applied to measles susceptibility data in Scotland among a series of cohorts of children who were aged 2.5-4.5, in September of the years 1998 to 2014.

Validation of the French national health insurance information system as a tool in vaccine safety assessment: application to febrile convulsions after pediatric measles/mumps/rubella immunization.

In the French national health insurance information system (SNIIR-AM), routine records of health claimed reimbursements are linked to hospital admissions for the whole French population. The main focus of this work is the usability of this system for vaccine safety assessment programme. Self-controlled case series analyses were performed using an exhaustive SNIIR-AM extraction of French children aged less than 3 years, to investigate the relationship between MMR immunization and children hospitalizations for febrile convulsions, a well-documented rare adverse event, over 2009-2010. The results suggest a significant increase of febrile convulsions during the 6-11 days period following any MMR immunization (IRR=1.49, 95% CI=1.22, 1.83; p=0.0001) and no increase 15-35 days post any MMR immunization (IRR=1.03, 95% CI=0.89, 1.18; p=0.72). These results are in accordance with other results obtained from large epidemiologic studies, which suggest the usability of the SNIIR-AM as a relevant database to study the occurrence of adverse events associated with immunization. For future use, results associated with risk of convulsion during the day of vaccination should nevertheless be considered with particular caution.

Epidemiological designs for vaccine safety assessment: methods and pitfalls.

Three commonly used designs for vaccine safety assessment post licensure are cohort, case-control and self-controlled case series. These methods are often used with routine health databases and immunisation registries. This paper considers the issues that may arise when designing an epidemiological study, such as understanding the vaccine safety question, case definition and finding, limitations of data sources, uncontrolled confounding, and pitfalls that apply to the individual designs. The example of MMR and autism, where all three designs have been used, is presented to help consider these issues.

A game dynamic model for vaccine skeptics and vaccine believers: measles as an example.

Widespread avoidance of Measles-Mumps-Rubella vaccination (MMR), with a consequent increase in the incidence of major measles outbreaks, demonstrates that the effectiveness of vaccination programs can be thwarted by the public misperceptions of vaccine risk. By coupling game theory and epidemic models, we examine vaccination choice among populations stratified into two behavioral groups: vaccine skeptics and vaccine believers. The two behavioral groups are assumed to be heterogeneous with respect to their perceptions of vaccine and infection risks. We demonstrate that the pursuit of self-interest among vaccine skeptics often leads to vaccination levels that are suboptimal for a population, even if complete coverage is achieved among vaccine believers. The demand for measles vaccine across populations driven by individual self-interest was found to be more sensitive to the proportion of vaccine skeptics than to the extent to which vaccine skeptics misperceive the risk of vaccine. Furthermore, as the number of vaccine skeptics increases, the probability of infection among vaccine skeptics increases initially, but it decreases once the vaccine skeptics begin receiving the vaccination, if both behavioral groups are vaccinated according to individual self-interest. Our results show that the discrepancy between the coverages of measles vaccine that are driven by self-interest and those driven by population interest becomes larger when the cost of vaccination increases. This research illustrates the importance of public education on vaccine safety and infection risk in order to maintain vaccination levels that are sufficient to maintain herd immunity.

Addressing the vaccine confidence gap.

Vaccines--often lauded as one of the greatest public health interventions--are losing public confidence. Some vaccine experts have referred to this decline in confidence as a crisis. We discuss some of the characteristics of the changing global environment that are contributing to increased public questioning of vaccines, and outline some of the specific determinants of public trust. Public decision making related to vaccine acceptance is neither driven by scientific nor economic evidence alone, but is also driven by a mix of psychological, sociocultural, and political factors, all of which need to be understood and taken into account by policy and other decision makers. Public trust in vaccines is highly variable and building trust depends on understanding perceptions of vaccines and vaccine risks, historical experiences, religious or political affiliations, and socioeconomic status. Although provision of accurate, scientifically based evidence on the risk-benefit ratios of vaccines is crucial, it is not enough to redress the gap between current levels of public confidence in vaccines and levels of trust needed to ensure adequate and sustained vaccine coverage. We call for more research not just on individual determinants of public trust, but on what mix of factors are most likely to sustain public trust. The vaccine community demands rigorous evidence on vaccine efficacy and safety and technical and operational feasibility when introducing a new vaccine, but has been negligent in demanding equally rigorous research to understand the psychological, social, and political factors that affect public trust in vaccines.

Dilemmas of a vitalizing vaccine market: lessons from the MMR vaccine/autism debate.

A number of issues related to vaccines and vaccinations in society are discussed in this paper. Our purpose is to merge an analysis of some recent changes in the vaccine market with social science research on the relationship between citizens and authorities. The article has two empirical parts. The first shows how the vaccine market, which for many years has had immense financial problems, nowadays seems to becoming economically vitalized, mostly due to the production of new and profitable vaccines. However prosperous the future may appear, certain reactions from the public regarding vaccination initiatives offer insight into inherent problems of vaccine policies in many Western countries. In the second part of the article, these problems are exemplified with the recent controversy over the MMR (measles, mumps, and rubella) vaccine. We conclude that in spite of the improving profit-margins, the vaccine market remains vulnerable and insecure. Vaccines are permeated by society, even more so than pharmaceutics that are used to cure or alleviate illnesses. Radical changes in financial conditions with promises of a more profitable market will not, we argue, solve other even more fundamental problems.

Anatomy of a health scare: education, income and the MMR controversy in the UK.

The measles, mumps and rubella (MMR) controversy provides an interesting case where, for a short period of time, research publicized in the media, suggested a potential risk of serious side-effects associated with the vaccine, where there was also a sharp behavioral response from the public, and where the initial information was subsequently overturned. We consider the controversy from the perspective of health inequalities and the assimilation of information, focusing on whether and how vaccine uptake behavior in the wake of the controversy differed among groups of parents by education and income. Using panel data on the variation in the uptake of the MMR, and other childhood immunizations, across local Health Authority areas we find that the uptake rate of the MMR declined faster in areas where a larger fraction of parents had stayed in education past the age of 18 than in areas with less educated parents. We also find that the same areas reduced their relative uptake of other uncontroversial childhood immunizations, suggesting a "spillover" effect. Using a supplementary data source we find evidence of a corresponding positive income effect, indicating that wealthier parents avoided the MMR dilemma by purchasing single vaccines.

Observational safety study of febrile convulsion following first dose MMRV vaccination in a managed care setting.

BACKGROUND: A combined measles, mumps, rubella, varicella live vaccine (MMRV, Merck and Co., Inc., US) was recently licensed in the US. Pre-licensure clinical trial data showed a significant increase in fever in days 5-12 following MMRV vaccination as compared to the vaccines given separately (MMR+V). This post-licensure retrospective cohort study was undertaken to assess the incidence of febrile convulsion following MMRV. METHODS: Children ages 12-60 months who received a first dose of MMRV in February 2006-June 2007 in a managed care organization were included in the study. Subjects were optimally matched on age, sex, and calendar date of vaccination to children who received MMR+V concomitantly in November 2003-January 2006, before MMRV licensure. Potential cases of febrile convulsion were identified through administrative data and adjudicated by expert panel, according to pre-specified criteria. RESULTS: During the 30 days post-vaccination, there were 128 and 94 potential convulsion cases among the 31,298 children in the MMRV and MMR+V cohorts, respectively. After review of available medical charts and adjudication, there were 84 cases of confirmed febrile convulsion, 44 (1.41/1000) and 40 (1.28/1000) in the MMRV and MMR+V cohorts, respectively (RR=1.10, 95% CI=0.72, 1.69). In days 5-12 following vaccination, a pre-specified period of interest, the respective numbers were 22 (0.70/1000) and 10 (0.32/1000) (RR=2.20, 95% CI=1.04, 4.65). CONCLUSION: These data suggest that the risk of febrile convulsion is increased in days 5-12 following vaccination with MMRV as compared to MMR+V given separately during the same visit, when post-vaccination fever and rash are also increased in clinical trials. While there was no evidence of an increase in the overall month following vaccination, the elevated risk during this time period should be communicated and needs to be balanced with the potential benefit of a combined vaccine.

Prevention is better than cure.

The history of the control of infectious disease reflects the balance between our understanding of the nature of infection, the mechanisms of host resistance and the available technology to deliver an intervention. However, behind this 'biomedical' construct lies a deeper set of issues which embody serendipity, public understanding, and population-based intervention and its acceptability by the wider community, often complicated by the decisions and subsequent vacillations of policy makers.