International Journal of Molecular Veterinary Research, 2024, Vol.14, No.5, 202-210 http://animalscipublisher.com/index.php/ijmvr 205 flocks (Sarma et al., 2019). These examples illustrate that well-designed vaccination programs not only enhance animal health but also contribute to the economic sustainability of poultry operations. 5 Case Study 5.1 Farm characteristics and trial design The study was conducted across various poultry farms with distinct characteristics to evaluate the efficacy of different vaccines in real-world settings. For instance, in central Ethiopia, smallholder farms were selected to test the Newcastle disease I2 vaccine using different delivery methods such as drinking water and spray, involving 20 households randomly assigned to intervention and control groups (Mebrahtu et al., 2018). Similarly, a large-scale field trial in Morocco involved 18 paired bird houses across 15 farms to assess the safety and efficacy of an aroA-deleted live vaccine against avian colibacillosis. These trials were designed to reflect the diverse conditions under which poultry farming occurs, ensuring that the results are applicable to a wide range of farming practices. 5.2 Trial results and observations The trials yielded significant insights into vaccine efficacy and safety. In the Ethiopian study, all vaccinated chickens survived a virulent Newcastle disease virus challenge, while only 40% of the unvaccinated group survived, demonstrating the vaccine's protective efficacy (Table 2) (Mebrahtu et al., 2018). In the Moroccan trial, vaccinated groups showed statistically significant improvements in mortality rates, weight gain, and reduced antibiotic use compared to controls, confirming the vaccine's efficacy against colibacillosis. Additionally, a study on a unique live virus vaccine for avian encephalomyelitis and fowlpox showed 100% protection against fowlpox and 97% against avian encephalomyelitis in field conditions, with no adverse reactions reported (Sarma et al., 2019). Table 2 Number of chicken owned and survived at the end of the study period in Minjar-Shenkora district (Adopted from Mebrahtu et al., 2018) No. owned No. died No. alive Survival Unvaccinated Total 151 102 49 32.45% Average/household 12.58 7.75 4.08 Vaccinated group Total 337 41 296 87.83% Average/household 21.06 2.56 18.5 5.3 Key takeaways and lessons learned The case studies highlight the importance of selecting appropriate vaccination methods and understanding farm-specific conditions to enhance vaccine efficacy. The Newcastle disease I2 vaccine's success in smallholder settings underscores the potential for alternative delivery methods like drinking water and spray to improve vaccination coverage in rural areas. The aroA-deleted live vaccine's performance in Morocco illustrates the benefits of tailored vaccination programs that consider local disease prevalence and farm management practices (Mombarg et al., 2014). These findings emphasize the need for continued research and adaptation of vaccination strategies to meet the diverse needs of poultry farms globally, ensuring both economic viability and animal health. 6 Factors Influencing Vaccine Efficacy 6.1 Biological factors Biological factors play a crucial role in determining the efficacy of vaccines in poultry farms. Genetic and epigenetic variations among chicken breeds can significantly influence vaccine responses. For instance, microRNAs (miRNAs) have been identified as key epigenetic factors that modulate vaccine efficacy by affecting gene expression related to immune responses. Studies have shown that different genetic lines of chickens exhibit varying levels of miRNA expression, which correlates with their level of protection against diseases like Marek's disease (Zhang et al., 2024). Additionally, the presence of maternal antibodies can interfere with the immune response to vaccines, necessitating the development of vaccines that can overcome this challenge (Meunier et al., 2015).
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