The Onchocerciasis Vaccine for Africa (TOVA): A new tool to help prevent, control and eliminate river blindness from Africa.
The International Community has set ambitious targets for elimination of onchocerciasis (river blindness) as a public health problem by 2025. Considerable progress has been made through annual and bi-annual mass treatment with ivermectin (MectizanTM) for periods of between 10 and 15 years. However, in areas of high prevalence, transmission of the infection persists after 20 years of mass treatment. Furthermore, disease modelling studies suggest that it may not be possible to achieve complete onchocerciasis elimination using ivermectin alone, even after 50 years of annual treatment (https://doi.org/10.1371/journal.pntd.0003664; https://doi.org/10.1371/journal.pntd.0002169).
WHO defines elimination as the reduction to zero of the incidence of an infection caused by a specific pathogen in a defined geographical area, with minimal risk of reintroduction. This is not eradication, which is the permanent [complete] removal a disease from the World.
If elimination of onchocerciasis is to be achieved on a more extensive scale, new and additional interventions will be required. A vaccine would complement and augment ivermectin treatment and address identifiable deficiencies in current ivermectin-based control programmes which exclude children under 5 years and cannot used in communities where onchocerciasis is co-endemic with loiasis, a second parasitic infection.
TOVA partners have been working towards the development of a vaccine for over 25 years. Three vaccine candidates have been selected based on their ability to evoke strong protective responses capable of reducing parasite burden of immunised animals by more than 90%.
TOVA aims to take at least one of these vaccine candidate through Phase I trials by 2025. The immediate task is to manufacture the vaccines and demonstrate their safety in accordance with national and international regulations and WHO guidelines.
The onchocerciasis vaccine is initially aimed at protecting pre-school children (<5 years of age). The vaccine will reduce adult worm burden and fecundity with consequential reduction in pathology associated with microfilariae.
In addition, a vaccine will find use in ongoing ivermectin control programmes and contribute to reduction in transmission rates; moreover, it will protect areas where local elimination may have been achieved.