Modeling the 2014 Ebola Virus Epidemic – Agent-Based Simulations, Temporal Analysis and Future Predictions for Liberia and Sierra Leone


We developed an agent-based model to investigate the epidemic dynamics of Ebola virus disease (EVD) in Liberia and Sierra Leone from May 27 to December 21, 2014. The dynamics of the agent-based simulator evolve on small-world transmission networks of sizes equal to the population of each country, with adjustable densities to account for the effects of public health intervention policies and individual behavioral responses to the evolving epidemic. Based on time series of the official case counts from the World Health Organization (WHO), we provide estimates for key epidemiological variables by employing the so-called Equation-Free approach. The underlying transmission networks were characterized by rather random structures in the two countries with densities decreasing by ~19% from the early (May 27-early August) to the last period (mid October-December 21). Our estimates for the values of key epidemiological variables, such as the mean time to death, recovery and the case fatality rate, are very close to the ones reported by the WHO Ebola response team during the early period of the epidemic (until September 14) that were calculated based on clinical data. Specifically, regarding the effective reproductive number Re, our analysis suggests that until mid October, Re was above 2.3 in both countries; from mid October to December 21, Re dropped well below unity in Liberia, indicating a saturation of the epidemic, while in Sierra Leone it was around 1.9, indicating an ongoing epidemic. Accordingly, a ten-week projection from December 21 estimated that the epidemic will fade out in Liberia in early March; in contrast, our results flashed a note of caution for Sierra Leone since the cumulative number of cases could reach as high as 18,000, and the number of deaths might exceed 5,000, by early March 2015. However, by processing the reported data of the very last period (December 21, 2014-January 18, 2015), we obtained more optimistic estimates indicative of a remission of the epidemic in Sierra Leone, as reflected by the derived Re (~0.82, 95% CI: 0.81-0.83).

Hesitancy, Trust and Individualism in Vaccination Decision-Making


Related Articles The article is part of the PLOS Currents Outbreaks “Vaccine Hesitancy Collection“. Editorial Based on recent trends, outbreaks of measles and other vaccine-preventable diseases could be more commonplace in the coming years, even in countries where such diseases have been considered eliminated or under control. In 2014, the United States reported over 600 [...]

Vaccine Narratives and Public Health: Investigating Criticisms of H1N1 Pandemic Vaccination


Vaccine hesitancy is often understood and explored on the level of individual decision-making. However, questions surrounding the risk and efficacy of vaccination are evident in wider public discourse; social narratives of vaccination inform and impact on the individual level. This paper takes a narrative analysis approach from the sociology of health to examine data drawn from a wider study on global public health responses to the H1N1 pandemic. The paper concentrates upon criticisms to mass vaccination as recounted within the Council of Europe’s debate of the handling of H1N1. It shows that three narratives were particularly dominant: problematizing the use of vaccination as a public health response; criticising the efficacy of the vaccines; and, questioning the safety of the strategy. This debate presents an important case study in understanding the way in which vaccines are problematized within the public discourse.

Factors Associated with Intention to Receive Influenza and Tetanus, Diphtheria, and Acellular Pertussis (Tdap) Vaccines during Pregnancy: A Focus on Vaccine Hesitancy and Perceptions of Disease Severity and Vaccine Safety


BACKGROUND: Improving influenza and tetanus, diphtheria and acellular pertussis (Tdap) vaccine coverage among pregnant women is needed.
PURPOSE: To assess factors associated with intention to receive influenza and/or Tdap vaccinations during pregnancy with a focus on perceptions of influenza and pertussis disease severity and influenza vaccine safety.
METHODS: Participants were 325 pregnant women in Georgia recruited from December 2012 – April 2013 who had not yet received a 2012/2013 influenza vaccine or a Tdap vaccine while pregnant. Women completed a survey assessing influenza vaccination history, likelihood of receiving antenatal influenza and/or Tdap vaccines, and knowledge, attitudes and beliefs about influenza, pertussis, and their associated vaccines.
RESULTS: Seventy-three percent and 81% of women believed influenza and pertussis, respectively, would be serious during pregnancy while 87% and 92% believed influenza and pertussis, respectively, would be serious to their infants. Perception of pertussis severity for their infant was strongly associated with an intention to receive a Tdap vaccine before delivery (p=0.004). Despite perceptions of disease severity for themselves and their infants, only 34% and 44% intended to receive antenatal influenza and Tdap vaccines, respectively. Forty-six percent had low perceptions of safety regarding the influenza vaccine during pregnancy, and compared to women who perceived the influenza vaccine as safe, women who perceived the vaccine as unsafe were less likely to intend to receive antenatal influenza (48% vs. 20%; p < 0.001) or Tdap (53% vs. 33%; p < 0.001) vaccinations.
CONCLUSIONS: Results from this baseline survey suggest that while pregnant women who remain unvaccinated against influenza within the first three months of the putative influenza season may be aware of the risks influenza and pertussis pose to themselves and their infants, many remain reluctant to receive influenza and Tdap vaccines antenatally. To improve vaccine uptake in the obstetric setting, our findings support development of evidence-based vaccine promotion interventions which emphasize vaccine safety during pregnancy and mention disease severity in infancy.

Why Are Young Adults Affected? Estimating Measles Vaccination Coverage in 20-34 Year Old Germans in Order to Verify Progress Towards Measles Elimination


The introduction of measles vaccination into routine childhood vaccination programmes has led to a shift of disease burden and incidence among young adults. This was confirmed by the recent rise in measles cases and outbreaks throughout Europe. To prevent outbreaks and eliminate measles, one of the key objectives of the WHO Europe measles elimination framework is achieving overall vaccination coverage of ≥95% in the population on a district level.
In the absence of national registers, data on vaccination coverage in Germany is recorded at the age of school entry, through insurance refund claim data and population studies. Vaccination status (VS) of young adults is largely unknown.

We assessed measles vaccination coverage in young adults aged 20-34 years on a district level of the German Federal State of Rhineland-Palatinate. The knowledge and attitude towards immunization of unvaccinated to vaccinated young adults were compared using Likert questions. We used proportional allocation for stratified random sampling across 36 counties. We mailed a self-administered questionnaire with pre-paid return envelopes along with an offer to complete online. Prior to calculating coverage we tested for non-responder bias using logistic regression.

465 (28%) of 1,637 persons contacted responded (mail: 23%, online: 5%). More women responded than men (odds ratio (OR)=2.1; 95% confidence intervall (CI)=1.7-2.6) but age did not vary between responders and non-responders. Vaccination coverage was 90% (95%CI=87%-93%) for one and 56% (95%CI=51%-61%) for two doses. We found a statistically significant association between receiving two doses and age group. The 20-24 years age group had a 2.3 higher incidence rate ratio (95%CI=1.7-3.2) than the reference group of 30-34 year old to have received two doses of measles vaccination. The group of 25-29 year old had a 1.5 higher incidence rate (95%CI=1.0-2.1) than the reference group to have received two doses of measles vaccination.

Coverage has failed to reach the WHO Europe elimination goal of 95% measles vaccination in the general population. Targeted approaches including enlistment of occupational health services and checking vaccination status during general practitioner (GP) visits are needed to increase vaccination uptake in this age group in order to achieve measles elimination.

Vaccine Hesitancy: Clarifying a Theoretical Framework for an Ambiguous Notion


Today, according to many public health experts, public confidence in vaccines is waning. The term “vaccine hesitancy” (VH) is increasingly used to describe the spread of such vaccine reluctance. But VH is an ambiguous notion and its theoretical background appears uncertain. To clarify this concept, we first review the current definitions of VH in the public health literature and examine its most prominent characteristics. VH has been defined as a set of beliefs, attitudes, or behaviours, or some combination of them, shared by a large and heterogeneous portion of the population and including people who exhibit reluctant conformism (they may either decline a vaccine, delay it or accept it despite their doubts) and vaccine-specific behaviours. Secondly, we underline some of the ambiguities of this notion and argue that it is more a catchall category than a real concept. We also call into question the usefulness of understanding VH as an intermediate position along a continuum ranging from anti-vaccine to pro-vaccine attitudes, and we discuss its qualification as a belief, attitude or behaviour. Thirdly, we propose a theoretical framework, based on previous literature and taking into account some major structural features of contemporary societies, that considers VH as a kind of decision-making process that depends on people’s level of commitment to healthism/risk culture and on their level of confidence in the health authorities and mainstream medicine.

Measuring Vaccine Confidence: Introducing a Global Vaccine Confidence Index


Public confidence in vaccination is vital to the success of immunisation programmes worldwide. Understanding the dynamics of vaccine confidence is therefore of great importance for global public health. Few published studies permit global comparisons of vaccination sentiments and behaviours against a common metric. This article presents the findings of a multi-country survey of confidence in vaccines and immunisation programmes in Georgia, India, Nigeria, Pakistan, and the United Kingdom (UK) – these being the first results of a larger project to map vaccine confidence globally.

Data were collected from a sample of the general population and from those with children under 5 years old against a core set of confidence questions. All surveys were conducted in the relevant local-language in Georgia, India, Nigeria, Pakistan, and the UK. We examine confidence in immunisation programmes as compared to confidence in other government health services, the relationships between confidence in the system and levels of vaccine hesitancy, reasons for vaccine hesitancy, ultimate vaccination decisions, and their variation based on country contexts and demographic factors.

The numbers of respondents by country were: Georgia (n=1000); India (n=1259); Pakistan (n=2609); UK (n=2055); Nigerian households (n=12554); and Nigerian health providers (n=1272). The UK respondents with children under five years of age were more likely to hesitate to vaccinate, compared to other countries. Confidence in immunisation programmes was more closely associated with confidence in the broader health system in the UK (Spearman’s ρ=0.5990), compared to Nigeria (ρ=0.5477), Pakistan (ρ=0.4491), and India (ρ=0.4240), all of which ranked confidence in immunisation programmes higher than confidence in the broader health system. Georgia had the highest rate of vaccine refusals (6 %) among those who reported initial hesitation. In all other countries surveyed most respondents who reported hesitating to vaccinate went on to receive the vaccine except in Kano state, Nigeria, where the percentage of those who ultimately refused vaccination after initially hesitating was as high as 76%) Reported reasons for hesitancy in all countries were classified under the domains of “confidence,” “convenience,” or “complacency,” and confidence issues were found to be the primary driver of hesitancy in all countries surveyed.

Assessing the Direct Effects of the Ebola Outbreak on Life Expectancy in Liberia, Sierra Leone and Guinea


Background: An EVD outbreak may reduce life expectancy directly (due to high mortality among EVD cases) and indirectly (e.g., due to lower utilization of healthcare and subsequent increases in non-EVD mortality). In this paper, we investigated the direct effects of EVD on life expectancy in Liberia, Sierra Leone and Guinea (LSLG thereafter).

Methods: We used data on EVD cases and deaths published in situation reports by the World Health Organization (WHO), as well as data on the age of EVD cases reported from patient datasets. We used data on non-EVD mortality from the most recent life tables published prior to the EVD outbreak. We then formulated three scenarios based on hypotheses about a) the extent of under-reporting of EVD cases and b) the EVD case fatality ratio. For each scenario, we re-estimated the number of EVD deaths in LSLG and we applied standard life table techniques to calculate life expectancy.

Results: In Liberia, possible reductions in life expectancy resulting from EVD deaths ranged from 1.63 year (low EVD scenario) to 5.56 years (high EVD scenario), whereas in Sierra Leone, possible life expectancy declines ranged from 1.38 to 5.10 years. In Guinea, the direct effects of EVD on life expectancy were more limited (<1.20 year).

Conclusions: Our high EVD scenario suggests that, due to EVD deaths, life expectancy may have declined in Liberia and Sierra Leone to levels these two countries had not experienced since 2001-2003, i.e., approximately the end of their civil wars. The total effects of EVD on life expectancy may however be larger due to possible concomitant increases in non-EVD mortality during the outbreak.

Whole Genome Sequencing for the Retrospective Investigation of an Outbreak of Salmonella Typhimurium DT 8


Salmonella enterica serovar Typhimurium DT8 is uncommon within the European Union. An increase in this phage type was reported in the summer of 2013 in the States of Jersey.

A total of 21 human cases with this phage type were microbiologically confirmed. Salmonella isolates from mayonnaise made using raw eggs were also confirmed as being Salmonella Typhimurium DT8. The epidemiological investigations strongly supported a link between mayonnaise consumption and illness. Whole genome sequencing (WGS) was used to retrospectively investigate this outbreak with a view to assess the similarity between the suspect food and the human isolates and to characterise a known point source outbreak to assist in development of algorithms for outbreak detection.

Sequence data showed that the outbreak associated isolates, including the food isolates, formed a tightly clustered monophyletic group, with a maximum pairwise distance of 3 single nucleotide polymorphisms.

WGS data is useful in confirming the causative agent of outbreaks where food and clinical isolates are available. This dataset, comprising a known outbreak, will be useful in the development of automatic algorithms for outbreak detection.

Temporal Changes in Ebola Transmission in Sierra Leone and Implications for Control Requirements: a Real-time Modelling Study


Background: Between August and November 2014, the incidence of Ebola virus disease (EVD) rose dramatically in several districts of Sierra Leone. As a result, the number of cases exceeded the capacity of Ebola holding and treatment centres. During December, additional beds were introduced, and incidence declined in many areas. We aimed to measure patterns of transmission in different regions, and evaluate whether bed capacity is now sufficient to meet future demand.

Methods: We used a mathematical model of EVD infection to estimate how the extent of transmission in the nine worst affected districts of Sierra Leone changed between 10th August 2014 and 18th January 2015. Using the model, we forecast the number of cases that could occur until the end of March 2015, and compared bed requirements with expected future capacity.

Results: We found that the reproduction number, R, defined as the average number of secondary cases generated by a typical infectious individual, declined between August and December in all districts. We estimated that R was near the crucial control threshold value of 1 in December. We further estimated that bed capacity has lagged behind demand between August and December for most districts, but as a consequence of the decline in transmission, control measures caught up with the epidemic in early 2015.

Conclusions: EVD incidence has exhibited substantial temporal and geographical variation in Sierra Leone, but our results suggest that the epidemic may have now peaked in Sierra Leone, and that current bed capacity appears to be sufficient to keep the epidemic under-control in most districts.