Development of a multivalent paediatric human vaccine for rabies virus in combination with Measles-Mumps-Rubella (MMR)

Study of the effectiveness of combined rabies-tetanus vaccine as compared to individual vaccines

Purpose

Effective treatment for animal bites is essential, encompassing immediate measures and protocols for rabies and tetanus vaccination. In this study, we evaluated the effectiveness of the administration of individual and combined rabies-tetanus (RT) vaccines in mice as model animals.

Materials and Methods

Animal groups were injected with either undiluted Toxovac® combined with Rabies vaccine® (RT/Group 1)/Speeda® (ST/Group 3), 2-fold diluted Toxovac® with Rabies vaccine® (RT1/2/Group 2), or purified tetanus toxoid with Speeda® (Spurf/Group 4). Mice were immunized with either 2 intraperitoneal (IP) doses at one-week interval or one subcutaneous (SC) dose for rabies immunogenicity, and with one SC dose for tetanus immunogenicity. The potency of the vaccines was determined through challenge test, while their immunogenicity was examined by measuring the anti-rabies and anti-tetanus immunoglobulin G response.

Results

All tested vaccines were potent except Spurf; tetanus was not potent. Rabies' immunogenicity for all combinations through both routes of administration showed comparable antibody response & non-significant difference (p≥0.05) at days 14 and 28 compared to single rabies injected by 2 IP doses. Tetanus' immunogenicity in combinations was compared with Toxovac®. RT depicted higher antibody response on both days 14 and 28. Whereas RT1/2 showed a non-significant difference on both days 14 and 28. Therefore, rabies has a synergistic effect on tetanus in combination.

Conclusion

The immune response to rabies in combination vaccine injected as a single SC dose was as effective as 2 IP doses of single vaccine. Our results highlight the potential of RT combination vaccine via SC as a cost-effective means to provide protective immunity.

New human rabies vaccines in the pipeline

Rabies remains endemic in more than 150 countries. In 99% of human cases, rabies virus is transmitted by dogs. The disease, which is nearly always fatal, is preventable by vaccines given either before and/or after exposure to a rabid animal. Numerous factors including the high cost of vaccines, the relative complexity of post-exposure vaccination protocols requiring multiple doses of vaccine, which in cases of severe exposure have to be combined with a rabies immune globulin, lack of access to health care, and insufficient surveillance contribute to the estimated 59,000 human deaths caused by rabies each year. New, less expensive and more immunogenic rabies vaccines are needed together with improved surveillance and dog rabies control to reduce the death toll of human rabies. Here, we discuss new rabies vaccines that are in clinical and pre-clinical testing and evaluate their potential to replace current vaccines.

Trying to treat the untreatable: experimental approaches to clear rabies virus infection from the CNS

Rabies virus causes an invariably fatal encephalitis following the onset of clinical disease. Despite the availability of safe and effective vaccines, the clinical stages of rabies encephalitis remain untreatable, with few survivors being documented. A principal obstacle to the treatment of rabies is the neurotropic nature of the virus, with the blood-brain barrier size exclusion limit rendering the delivery of antiviral drugs and molecules to the central nervous system inherently problematic. This review focuses on efforts to try and overcome barriers to molecule delivery to treat clinical rabies and overviews current progress in the development of experimental live rabies virus vaccines that may have future applications in the treatment of clinical rabies, including the attenuation of rabies virus vectors through either the duplication or mutation of existing genes or the incorporation of non-viral elements within the genome. Rabies post-infection treatment (PIT) remains the holy grail of rabies research.

Rabies

Rabies is a life-threatening neglected tropical disease: tens of thousands of cases are reported annually in endemic countries (mainly in Africa and Asia), although the actual numbers are most likely underestimated. Rabies is a zoonotic disease that is caused by infection with viruses of the Lyssavirus genus, which are transmitted via the saliva of an infected animal. Dogs are the most important reservoir for rabies viruses, and dog bites account for >99% of human cases. The virus first infects peripheral motor neurons, and symptoms occur after the virus reaches the central nervous system. Once clinical disease develops, it is almost certainly fatal. Primary prevention involves dog vaccination campaigns to reduce the virus reservoir. If exposure occurs, timely post-exposure prophylaxis can prevent the progression to clinical disease and involves appropriate wound care, the administration of rabies immunoglobulin and vaccination. A multifaceted approach for human rabies eradication that involves government support, disease awareness, vaccination of at-risk human populations and, most importantly, dog rabies control is necessary to achieve the WHO goal of reducing the number of cases of dog-mediated human rabies to zero by 2030.

Current Status and Development of Vaccines and Other Biologics for Human Rabies Prevention

Rabies is a neglected viral zoonosis with the highest case fatality of any infectious disease. Pasteur's historical accomplishments during the late 19(th) century began the process of human vaccine development, continuing to evolve into the 21(st) century. Over the past 35 years, great improvements occurred in the production of potent tissue culture vaccines and the gradual removal from the market of unsafe nerve tissue products. Timely and appropriate administration of modern biologics virtually assures survivorship, even after severe exposures. Nevertheless, in the developing world, if not provided for free nationally, the cost of a single course of human prophylaxis exceeds the average monthly wage of the common worker. Beyond traditional approaches, recombinant, sub-unit and other novel methods are underway to improve the availability of safe, effective and more affordable rabies biologics.

Rabies: Rare Human Infection - Common Questions

Rabies is an acute, rapidly progressive encephalitis that is almost always fatal. Prophylaxis is highly effective but economics limits disease control. The mechanism of death from rabies is unclear. It is poorly cytopathic and poorly inflammatory. Rabies behaves like an acquired metabolic disorder. There may be a continuum of disease severity. History of animal bite is rare. The diagnosis is often missed. Intermittent encephalopathy, dysphagia, hydrophobia and aerophobia, and focal paresthesias or myoclonic jerks suggest rabies. Laboratory diagnosis is cumbersome but sensitive. Treatment is controversial but survivors are increasingly reported, with good outcomes in 4 of 8 survivors.