Development and evaluation of a novel vaccine storage device for effective vaccination strategy against rabies
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Date
2023
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Publisher
Sokoine University of Agriculture
Abstract
Canine-mediated human rabies has the highest case fatality rate of any known infectious
disease and kills approx. 59,000 people annually, with most deaths being children under 15
years. The vast majority (99%) of these fatalities occur in Africa and Asia, where access to
appropriate Post Exposure Prophylaxis (PEP) is limited and where canine vaccination is
either inconsistently applied or, commonly, non-existent. Epidemiological studies have
shown that rabies has epidemiological features that make elimination a realistic and
feasible goal, with success demonstrated by comprehensive mass dog vaccination
programmes in the Americas, Western Europe and Japan. In rabies endemic countries,
dogs are often vaccinated using annually delivered central point clinics at the village level
on an annual basis. For this method to be effective at least 70% of the dog population must
be vaccinated to maintain herd immunity between campaigns. However, studies have
shown that only a few programmes utilising this approach have attained this level of
coverage, highlighting the need for alternative approaches to address this challenge.
The current study was carried out to develop an alternative strategy for delivering and
maintaining herd immunity over time in low-resource field settings. Through an iterative
process of improvement and testing with local communities in northern Tanzania, a passive
cooling device “Zeepot” for storage of thermotolerant rabies vaccines was developed at a
cost of $11 per unit. The results from a non-inferiority randomised controlled trial showed
that the serological response of dogs vaccinated using Nobivac ® Rabies vaccine stored
within the Zeepot was not inferior to the response of dogs vaccinated using cold-chain
stored vaccine (z = 1.1, df = 313, p-value = 0.25). Indeed, the 28-day post vaccination
group geometric mean titre was 1.8 IU/ml and 2.0 IU/ml for dogs vaccinated with vaccines
stored under cold-chain versus non-cold-chain respectively. Moreover, the percentage of
dogs that seroconverted in each arm was almost identical (85%). There was a positive
linear trend between Body Condition Score (O.R. 2.2, 95% CI: 1.1 – 5.1) and
seroconversion, suggesting that dogs of poor condition may not respond as expected to
vaccination. Our study demonstrated that the potency of Nobivac ® Rabies vaccine is not
impacted following storage in Zeepot Clay locally designed Passive Cooling Device.
A total of 17,571 dogs were vaccinated in the field study that was conducted to evaluate
the effectiveness of the standard delivery method also known as Central Point Vaccination
(CPV) and a novel strategy, Decentralized Continuous Vaccination (DCV), 2654 dogs
were vaccinated using CPV and 14,917 dogs were vaccinated through three sub-strategies
of DCV. At time point 1 (1 month after the initial vaccination campaign), the vaccination
coverage achieved by DCV coverage was higher (64.10%; 95CI 62.12 – 66.04) than for
CPV (35.86%; 95CI 32.59 – 39.51). Similarly, at time point 2 (11 months after the
vaccination campaign) the coverage in DCV (60.67%; 95CI 58.47 – 62.84) remained high
while the coverage in pulse vaccination was lower (32.10%; 95CI 28.82-35.57). Overall, >
84% of the respondents were satisfied with the vaccination services they received. DCV
has the potential to consistently maintain population level immunity.
Overall, this thesis showed that Zeepot Clay has a utility for storing thermotolerant
vaccines at sub-ambient temperatures. Moreover, DCV has the potential to
consistently maintain population level immunity making it a useful strategy to further
investigate for scaling up of mass dog vaccination in East Africa. Together the
findings of this work have potential application for rabies elimination programmes,
particularly in achieving the global target of zero human deaths by 2030 and
potentially for use in other vaccination programmes aiming to reach remote or
inaccessible communities.
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Thesis
Keywords
Novel vaccine storage, Vaccination strategy, Rabies, Post exposure prophylaxis, Children under 15 years