Journal of Vaccine Research, 2025, Vol.15, No.1, 1-9 http://medscipublisher.com/index.php/jvr 4 intake for each poultry, and the efficacy also depends on the feeding and drinking behaviors of the poultry, which may affect the efficacy of the vaccine (Renu et al., 2020; Jia et al., 2023). Spray and gel inoculation methods can enhance vaccine absorption and reduce stress in poultry, but careful operation is required to ensure that each poultry is evenly vaccinated. 3.3 Individual and large-scale vaccination: application scenarios in different production systems Individual vaccination, such as the injection method, is generally used in high-value breeding poultry or small-scale poultry flocks, because in such cases, it is relatively easy to precisely control the vaccine dosage and observe the vaccination effect (Peebles, 2018). This vaccination method can provide targeted protection and is suitable for those vaccines that require strict vaccination procedures or where large-scale vaccination is not very realistic. Large-scale vaccination methods, including drinking water, spraying and in-egg inoculation, are indispensable for large-scale commercial poultry farming and can efficiently vaccinate tens of thousands of poultry. These methods can reduce labor costs and the stress of poultry, and are very suitable for the breeding of broilers and laying hens. Whether to choose individual vaccination or large-scale vaccination depends on the size of the poultry flock, breeding goals, disease risks and existing resources. In intensive breeding, large-scale vaccination is more popular because it can flexibly expand the scale and is highly practical (Peebles, 2018; Saeed et al., 2019; Ravikumar et al., 2022). 4 Comparison of the Effectiveness of Vaccination Strategies 4.1 Protection rate, duration of immunity and adaptability to antigenic variations In poultry vaccination, the immune protection effects brought by different strategies are not the same. Compared with using only one type of vaccine, the combined use of attenuated live vaccines and inactivated booster vaccines, etc., usually enables poultry to produce higher antibody levels, stronger cellular immune responses, and better protective effects against diseases (Buharideen et al., 2021; Liu et al., 2022). The duration of immune protection is related to the type of vaccine and the timing of vaccination. For example, vaccinating poultry at hatcheries can make the immune level of the entire flock higher and more uniform. For viruses like avian influenza that are prone to mutation, in order for vaccines to adapt to antigen changes, it is necessary to update the vaccine strains regularly to ensure the protective effect (Figure 2) (Azzouguen et al., 2020; Ravikumar et al., 2022; Michel et al., 2023). Figure 2 Spatial distribution of the poultry population immunity against AI according to the different vaccination strategies (S) tested in the model (Adopted from Azzouguen et al., 2020) Nowadays, people are developing vaccines and new vaccination strategies that offer extensive protection, such as DNA primer/protein booster vaccines and recombinant vector vaccines, to address the issue of antigen variation and provide long-term cross-immune protection for poultry (Ravikumar et al., 2022; Liu et al., 2022). However,
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