Prophylactic mass vaccination programmes are not a realistic option in the battle to prevent new Ebolavirus outbreaks, a University of Kent-led research team has shown.
The findings come as the World Health Organisation has announced a new Ebola virus outbreak in the Democratic Republic of Kongo.
The team analysed the prospects for various Ebolavirus vaccines and found that, for the foreseable future at least, Ebolavirus outbreak control depends on surveillance and the isolation of cases.
The researchers' analysis revealed that very high proportions of potentially affected populations would need to be protected by vaccination to establish herd immunity, i.e. the level of immunity that prevents virus transmission within a population.
The study, entitled Herd immunity to Ebolaviruses is not a realistic target for current vaccination strategies identified that, in the critical phases of many Ebola virus outbreaks, the average infected individual infects four or more other people, which enables the virus to spread rapidly.
At this level, 80% of a population would need to be immunised to prevent outbreaks, even if a highly effective vaccine that protects 90% of individuals after vaccination was available.
Such vaccination rates are currently unachievable. In a vaccination trial during the West African Ebola virus epidemic, only 49% of individuals who had been in contact with Ebola virus patients could be vaccinated. Thirty-four per cent of contacts refused vaccination although they had been exposed to the disease.
There are currently no clinical vaccine candidates available that protect against all four human-pathogenic Ebolaviruses. It also remains unclear, say the researchers led by Professor Martin Michaelis, of Kent's School of Biosciences, whether the available vaccine candidates provide the long-term protection (? 10 years) that is required for the sort of prophylactic mass vaccination programme that could prevent Ebola, which becomes repeatedly introduced into the human population from animal reservoirs.
A large vaccination programme would also be costly and impractical, the study points out. Costs for current Ebolavirus vaccine candidates are estimated to be in a range of US$ 15-20 per dose, with some 462 million people living in the areas affected by Ebolavirus outbreaks, many of them in very remote rural areas.
In the absence of a realistic prophylactic mass vaccination programme, the reasearchers conclude that clinical vaccine candidates will need to be focused on health care workers who are often involved in disease transmission, potentially in combination with the vaccination of patient contacts.
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The study Herd immunity to Ebolaviruses is not a realistic target for current vaccination strategies (Martin Michaelis, Mark Wass, Stuart Masterson - University of Kent; Leslie Lobel - Ben Gurion University of the Negev, Beer Sheva, Israel and Uganda Virus Research Institute, Entebbe, Uganda; Miles Carroll - Public Health England, Porton Down, Salisbury) is published in the journal Frontiers in Immunology. See: https://www.frontiersin.org/articles/10.3389/fimmu.2018.01025/full
For more information or interview requests contact Martin Herrema at the University of Kent Press Office.
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Notes to editors
1. Four Ebolaviruses cause life-threatening disease in humans: Ebola virus (formerly known as Zaire ebolavirus), Sudan virus, Bundibugyo virus, and Taï Forest virus. The recent Ebola virus outbreak in West Africa resulted in at least 28,616 disease cases and 11,310 deaths. It demonstrated that Ebolaviruses can cause large outbreaks and resulted in an increased interest into vaccination programmes that prevent future outbreaks.
2. Established in 1965, the University of Kent - the UK's European university - now has almost 20,000 students across campuses or study centres at Canterbury, Medway, Tonbridge, Brussels, Paris, Athens and Rome.
It has been ranked 22nd in the Guardian University Guide 2018 and 25th in the Complete University Guide 2018, and in June 2017 was awarded a gold rating, the highest, in the UK Government's Teaching Excellence Framework (TEF).In the Times Higher Education (THE) World University Rankings 2015-16, it is in the top 10% of the world's leading universities for international outlook and 66th in its table of the most international universities in the world. The THE also ranked the University as 20th in its 'Table of Tables' 2016.
Kent is ranked 17th in the UK for research intensity (REF 2014). It has world-leading research in all subjects and 97% of its research is deemed by the REF to be of international quality.
In the National Student Survey 2016, Kent achieved the fourth highest score for overall student satisfaction, out of all publicly funded, multi-faculty universities. Along with the universities of East Anglia and Essex, Kent is a member of the Eastern Arc Research Consortium.
The University is worth £0.7 billion to the economy of the south east and supports more than 7,800 jobs in the region. Student off-campus spend contributes £293.3m and 2,532 full-time-equivalent jobs to those totals.
Kent has received two Queen's Anniversary prizes for Higher and Further Education.
Journal
Frontiers in Immunology