Differences between coverage of yellow fever vaccine and the first dose of measles-containing vaccine: A desk review of global data sources

Yellow fever vaccine coverage and associated factors among under-five children in Kenya: Data from Kenyan Demographic and Health Survey 2022

Yellow fever is a vaccine preventable hemorrhagic disease that leads to morbidity and mortality in the affected individuals. The only options for preventing and controlling its spread are through vaccination. Therefore, this study was conducted to estimate yellow fever vaccination coverage and associated factors among under-five children in Kenya. The total weighted samples of 2,844 children aged under-five were included in this study. The data were taken from the Kenyan Demographic and Health Survey 2022. In the multivariable analysis, the adjusted odds ratio with a 95% CI was used to declare significant associations of yellow fever vaccine. The yellow fever vaccine coverage among children aged under-five in Kenya was 18.50%. The significant factors associated with yellow fever vaccine coverage were: the age of the child older than 24 months (AOR = 1.7; 95% CI (1.17-2.58)); higher odds of yellow fever vaccination coverage was observed among older children, place of residence (AOR = 1.76; 95% CI (1.04-2.97)); higher odds was observed among urban residents, maternal education; primary education (AOR = 1.99; 95% CI (1.04-2.97)), secondary education (AOR = 2.85; 95% CI (1.41-5.76)), mothers who attended primary or secondary education have higher odds of yellow fever vaccination coverage, wealth index (AOR = 2.38; 95% CI (1.15-4.91)); higher odds of vaccination coverage was observed among poor households. Yellow fever vaccine coverage among under-five children in Kenya was low and has become an important public health concern. Policymakers and other stakeholders are recommended to focus on vaccination programs to prevent yellow fever disease.

A Systematic Review of Yellow Fever Outbreaks and Public Health Responses in Nigeria

Background

Yellow fever (YF) outbreaks continue to occur in Nigeria with a high mortality rate despite a well-established mode of transmission and the availability of a potent vaccine. This review is aimed at describing the epidemiology, determinants, and public health responses of yellow fever outbreaks in Nigeria from 1864 to 2020.

Methodology

The guidelines for the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) were used to conduct the review from November 2020 to April 2021. PubMed database, WHO library databases, and Google Scholar were used to search for relevant published materials including original and reviewed articles, conference papers and case reports from 1864 to 2020.

Results

Forty - eight articles and reports were included in the final reviews. Twenty - three outbreaks were described involving 33,830 suspected, presumptive, or confirmed cases of yellow fever and 8,355 deaths. The outbreaks occurred in every state of Nigeria including the Federal Capital Territory mostly during the rainy season. Low immunity in the population or low vaccination coverage, poor vector control, rainforest or savanna vegetation, rural-urban migration, and imported virus by travelers were common determinants noted. Public health responses have been through, centrally coordinated laboratory support, case management, emergency immunization, vector control, and surveillance.

Conclusion

Yellow fever outbreaks have increased in frequency and geographical spread with associated mortality rates. To stem the tide, mass immunization with 17D vaccines is encouraged, planned urbanization with adequate vector control measures enforced, effective case definition, vector surveillance, and effective awareness campaigns should be emphasized.

Availability of the Yellow Fever Vaccine in Primary Health Care Services in Brazil

Objectives

To analyze the availability of the Yellow Fever (YF) vaccine at Primary Health Care (PHC) services located in areas with vaccine recommendation in Brazil between two different periods.

Methods

Secondary data from the Program for Improving Access and Quality in PHC, with 13,666 services in 2013-14, and 19,125 in 2017-18, were used. A structured questionnaire was used for the data collection. Pearson’s chi-square and thematic cartographic maps were used to analyze the frequency of the YF vaccine, and Poisson regression with robust variances was used to analyze the associated factors.

Results

The overall frequency of PHC facilities with YF vaccine always available increased from 87.0% (CI 95%; 86.4-87.5) in 2013-14 to 89.7% (CI 95%; 89.2-90.1) in 2017-18. Facilities located in the South, Southeast, Midwest and Northern regions and in non-state capitals, as well as centers that had adequate facilities for vaccination actions, as well as an adey -50quate cold chain network, showed a greater prevalence of YF vaccine always available.

Conclusion

The frequency of a steady supply of YF vaccine available at PHC facilities, located in Areas with Routine Vaccination Recommendations, increased between 2013-14 and 2017-18. Geographical and structural characteristics related to vaccine actions at PHC facilities influenced access. The effective supply chain networks for the YF vaccine, together with adequate services at PHC facilities are essential to ensuring that the YF vaccine is always available.

The resurgence of yellow fever outbreaks in Nigeria: a 2-year review 2017-2019

Background

Yellow fever outbreaks are documented to have a considerable impact not only on the individuals but on the health system with significant economic implications. Efforts to eliminate yellow fever outbreaks globally through the EYE strategy remains important following outbreaks in Africa, Nigeria included. The outbreaks reported in Nigeria, since 2017 and the response efforts provide an opportunity to document and guide interventions for improving future outbreaks in Nigeria and other countries in Africa.

Methods

We reviewed the available yellow fever surveillance and vaccination response data between September 2017 and September 2019 across the 36 states across Nigeria. We described the epidemiology of the difference outbreaks and the periods for all interventions. We also documented the emergency vaccination responses as well as preventive mass vaccinations implemented towards improving population immunity and limiting epidemic potentials in Nigeria.

Results

A total of 7894 suspected cases with 287 laboratory-confirmed cases were reported in Nigeria between September 2017 and September 2019 with a mean age of 19 years and a case fatality of 2.7% amongst all reported cases. Outbreaks were confirmed in 55 LGAs with most of the outbreaks across four major epicentres in Kwara/Kogi, Edo, Ebonyi and Bauchi states. In response to these outbreaks, eight reactive vaccination campaigns, supported through ICG applications, were implemented. The duration for responding to the outbreaks ranged from 15 to 132 days (average 68 days) and a total of 45,648,243 persons aged < 45 years vaccinated through reactive and preventive mass campaigns between September 2017 and September 2019.

Conclusions

Nigeria experienced intermediate outbreaks of yellow fever between September 2017 and 2019 with vaccination responses conducted to control these outbreaks. However, there are delays in the timeliness of responses and more efforts required in improving reporting, response times and preparedness to further prevent morbidity and mortality from the yellow fever disease outbreaks. These efforts, including improving routine yellow fever coverage, contribute towards improving population immunity and other activities related to achieving the goals of the EYE strategy.

Review of data and knowledge gaps regarding yellow fever vaccine-induced immunity and duration of protection

Yellow fever (YF) virus is a mosquito-borne flavivirus found in Sub-Saharan Africa and tropical South America. The virus causes YF, a viral hemorrhagic fever, which can be prevented by a live-attenuated vaccine, strain 17D. Despite the vaccine being very successful at decreasing disease risk, YF is considered a re-emerging disease due to the increased numbers of cases in the last 30 years. Until 2014, the vaccine was recommended to be administered with boosters every 10 years, but in 2014 the World Health Organization recommended removal of booster doses for all except special populations. This recommendation has been questioned and there have been reports of waning antibody titers in adults over time and more recently in pediatric populations. Clearly, the potential of waning antibody titers is a very important issue that needs to be carefully evaluated. In this Perspective, we review what is known about the correlate of protection for full-dose YF vaccine, current information on waning antibody titers, and gaps in knowledge. Overall, fundamental questions exist on the durability of protective immunity induced by YF vaccine, but interpretation of studies is complicated by the use of different assays and different cut-offs to measure seroprotective immunity, and differing results among certain endemic versus non-endemic populations. Notwithstanding the above, there are few well-characterized reports of vaccine failures, which one would expect to observe potentially more with the re-emergence of a severe disease. Overall, there is a need to improve YF disease surveillance, increase primary vaccination coverage rates in at-risk populations, and expand our understanding of the mechanism of protection of YF vaccine.