Assessing the impact of preventive mass vaccination campaigns on yellow fever outbreaks in Africa: A population-level self-controlled case series study

A proposed One Health approach to control yellow fever outbreaks in Uganda

Yellow Fever (YF) is an acute viral hemorrhagic disease. Uganda is located within the Africa YF belt. Between 2019 and 2022, the Ugandan Health Authorities reported at least one outbreak of YF annually with an estimated 892 suspected cases, on average per year. The persistent recurrence of this disease raises significant concerns about the efficacy of current response strategies and prevention approaches. YF has been recognized as a One Health issue due to its interrelatedness with the animal and environmental domains. Monkeys have been recognized as the virus primary reservoir. The YF virus is transmitted through bites of infected Aedes or Haemagogus species mosquitoes between monkeys and humans. Human activities, monkey health, and environmental health issues (e.g., climate change and land use) impact YF incidence in Uganda. Additionally, disease control programs for other tropical diseases, such as mosquitoes control programs for malaria, impact YF incidence.This review adopts the One Health approach to highlight the limitations in the existing segmented YF control and prevention strategies in Uganda, including the limited health sector surveillance, the geographically localized outbreak response efforts, the lack of a comprehensive vaccination program, the limited collaboration and communication among relevant national and international agencies, and the inadequate vector control practices. Through a One Health approach, we propose establishing a YF elimination taskforce. This taskforce would oversee coordination of YF elimination initiatives, including implementing a comprehensive surveillance system, conducting mass YF vaccination campaigns, integrating mosquito management strategies, and enhancing risk communication. It is anticipated that adopting the One Health approach will reduce the risk of YF incidence and outbreaks.

Estimation and reduction of bias in self-controlled case series with non-rare event dependent outcomes and heterogeneous populations

The self-controlled case series (SCCS) is a commonly adopted study design in the assessment of vaccine and drug safety. Recurrent event data collected from SCCS studies are typically analyzed using the conditional Poisson model which assumes event times are independent within-cases. This assumption is violated in the presence of event dependence, where the occurrence of an event influences the probability and timing of subsequent events. When event dependence is suspected in an SCCS study, the standard recommendation is to include only the first event from each case in the analysis. However, first event analysis can still yield biased estimates of the exposure relative incidence if the outcome event is not rare. We first demonstrate that the bias in first event analysis can be even higher than previously assumed when subpopulations with different baseline incidence rates are present and describe an improved method for estimating this bias. Subsequently, we propose a novel partitioned analysis method and demonstrate how it can reduce this bias. We provide a recommendation to guide the number of partitions to use with the partitioned analysis, illustrate this recommendation with an example SCCS study of the association between beta-blockers and acute myocardial infarction, and compare the partitioned analysis against other SCCS analysis methods by simulation.

Interventions for improving coverage of childhood immunisation in low- and middle-income countries

BACKGROUND

Immunisation plays a major role in reducing childhood morbidity and mortality. Getting children immunised against potentially fatal and debilitating vaccine-preventable diseases remains a challenge despite the availability of efficacious vaccines, particularly in low- and middle-income countries. With the introduction of new vaccines, this becomes increasingly difficult. There is therefore a current need to synthesise the available evidence on the strategies used to bridge this gap. This is a second update of the Cochrane Review first published in 2011 and updated in 2016, and it focuses on interventions for improving childhood immunisation coverage in low- and middle-income countries.

OBJECTIVES

To evaluate the effectiveness of intervention strategies to boost demand and supply of childhood vaccines, and sustain high childhood immunisation coverage in low- and middle-income countries.

SEARCH METHODS

We searched CENTRAL, MEDLINE, CINAHL, and Global Index Medicus (11 July 2022). We searched Embase, LILACS, and Sociological Abstracts (2 September 2014). We searched WHO ICTRP and ClinicalTrials.gov (11 July 2022). In addition, we screened reference lists of relevant systematic reviews for potentially eligible studies, and carried out a citation search for 14 of the included studies (19 February 2020).

SELECTION CRITERIA

Eligible studies were randomised controlled trials (RCTs), non-randomised RCTs (nRCTs), controlled before-after studies, and interrupted time series conducted in low- and middle-income countries involving children that were under five years of age, caregivers, and healthcare providers.

DATA COLLECTION AND ANALYSIS

We independently screened the search output, reviewed full texts of potentially eligible articles, assessed the risk of bias, and extracted data in duplicate, resolving discrepancies by consensus. We conducted random-effects meta-analyses and used GRADE to assess the certainty of the evidence.

MAIN RESULTS

Forty-one studies involving 100,747 participants are included in the review. Twenty studies were cluster-randomised and 15 studies were individually randomised controlled trials. Six studies were quasi-randomised. The studies were conducted in four upper-middle-income countries (China, Georgia, Mexico, Guatemala), 11 lower-middle-income countries (Côte d'Ivoire, Ghana, Honduras, India, Indonesia, Kenya, Nigeria, Nepal, Nicaragua, Pakistan, Zimbabwe), and three lower-income countries (Afghanistan, Mali, Rwanda). The interventions evaluated in the studies were health education (seven studies), patient reminders (13 studies), digital register (two studies), household incentives (three studies), regular immunisation outreach sessions (two studies), home visits (one study), supportive supervision (two studies), integration of immunisation services with intermittent preventive treatment of malaria (one study), payment for performance (two studies), engagement of community leaders (one study), training on interpersonal communication skills (one study), and logistic support to health facilities (one study). We judged nine of the included studies to have low risk of bias; the risk of bias in eight studies was unclear and 24 studies had high risk of bias. We found low-certainty evidence that health education (risk ratio (RR) 1.36, 95% confidence interval (CI) 1.15 to 1.62; 6 studies, 4375 participants) and home-based records (RR 1.36, 95% CI 1.06 to 1.75; 3 studies, 4019 participants) may improve coverage with DTP3/Penta 3 vaccine. Phone calls/short messages may have little or no effect on DTP3/Penta 3 vaccine uptake (RR 1.12, 95% CI 1.00 to 1.25; 6 studies, 3869 participants; low-certainty evidence); wearable reminders probably have little or no effect on DTP3/Penta 3 uptake (RR 1.02, 95% CI 0.97 to 1.07; 2 studies, 1567 participants; moderate-certainty evidence). Use of community leaders in combination with provider intervention probably increases the uptake of DTP3/Penta 3 vaccine (RR 1.37, 95% CI 1.11 to 1.69; 1 study, 2020 participants; moderate-certainty evidence). We are uncertain about the effect of immunisation outreach on DTP3/Penta 3 vaccine uptake in children under two years of age (RR 1.32, 95% CI 1.11 to 1.56; 1 study, 541 participants; very low-certainty evidence). We are also uncertain about the following interventions improving full vaccination of children under two years of age: training of health providers on interpersonal communication skills (RR 5.65, 95% CI 3.62 to 8.83; 1 study, 420 participants; very low-certainty evidence), and home visits (RR 1.29, 95% CI 1.15 to 1.45; 1 study, 419 participants; very low-certainty evidence). The same applies to the effect of training of health providers on interpersonal communication skills on the uptake of DTP3/Penta 3 by one year of age (very low-certainty evidence). The integration of immunisation with other services may, however, improve full vaccination (RR 1.29, 95% CI 1.16 to 1.44; 1 study, 1700 participants; low-certainty evidence).

AUTHORS' CONCLUSIONS

Health education, home-based records, a combination of involvement of community leaders with health provider intervention, and integration of immunisation services may improve vaccine uptake. The certainty of the evidence for the included interventions ranged from moderate to very low. Low certainty of the evidence implies that the true effect of the interventions might be markedly different from the estimated effect. Further, more rigorous RCTs are, therefore, required to generate high-certainty evidence to inform policy and practice.

Association between Conflict and Cholera in Nigeria and the Democratic Republic of the Congo

Cholera outbreaks contribute substantially to illness and death in low- and middle-income countries. Cholera outbreaks are associated with several social and environmental risk factors, and extreme conditions can act as catalysts. A social extreme known to be associated with infectious disease outbreaks is conflict, causing disruption to services, loss of income, and displacement. To determine the extent of this association, we used the self-controlled case-series method and found that conflict increased the risk for cholera in Nigeria by 3.6 times and in the Democratic Republic of the Congo by 2.6 times. We also found that 19.7% of cholera outbreaks in Nigeria and 12.3% of outbreaks in the Democratic Republic of the Congo were attributable to conflict. Our results highlight the value of providing rapid and sufficient assistance during conflict-associated cholera outbreaks and working toward conflict resolution and addressing preexisting vulnerabilities, such as poverty and access to healthcare.