Currently, with the rapid development of large-scale and intensive farming in China, the popularity of vaccines in modern farming is increasing, and vaccine immunization has become one of the important measures for disease prevention and treatment in large-scale farms. However, some farms have varying levels of antibodies after immunization, and even cases of disease still occur. Therefore, it is crucial to carefully analyze the factors that affect animal immunity and improve measures related to animal immunization for the prevention and control of animal diseases in livestock and poultry. Below is a brief analysis of the factors that affect the immune response of vaccines.

1、 Vaccine factors

1. Vaccine quality

The quality of vaccines is the most direct factor affecting the immune efficacy of vaccines. Insufficient effective antigen content can directly lead to immune failure or insufficient antibody potency after immunization. The quality of vaccine adjuvants can affect vaccine absorption, antibody immune response, and avian stress. In addition, vaccine production processes such as emulsification, antigen concentration, and antigen inactivation of inactivated vaccines can affect vaccine particle size, endotoxin, formaldehyde, and heteroprotein content, thereby affecting vaccine absorption and the production performance of poultry populations with severe immune responses. Therefore, vaccine products with national approval numbers should be purchased through formal channels, and the vaccine varieties should be consistent with the local epidemic strains. Homemade vaccines and vaccines without approval numbers should not be used to ensure vaccine quality.

2. Transportation and storage of vaccines

Improper transportation and storage methods of vaccines, such as high temperatures during transportation, prolonged exposure to direct sunlight, prolonged storage beyond the expiration date of vaccines, freezing of inactivated vaccines or refrigeration of attenuated vaccines during storage, can all lead to a decrease in vaccine potency, resulting in poor immune efficacy or even immune failure. In addition, for some special vaccines such as liquid nitrogen Marek's disease vaccines, strict adherence to the operating procedures provided by the manufacturer should be followed, and designated professional technicians should be responsible for storage and dilution.

3. Vaccine usage method

Improper vaccine dilution method: Failure to dilute according to the ratio specified in the product manual, and failure to use up the vaccine within the specified time after dilution; Improper vaccine mixing: Mixing incompatible drugs or other vaccines into vaccines, and uneven mixing of vaccines from different manufacturers, may cause poor vaccine uptake and affect the effectiveness of immunization.

2、 Operational factors

Improper immune procedures can directly affect the effectiveness of immunity. Excessive vaccination can inhibit antibody formation and lead to immune tolerance or inflammatory reactions; The vaccination dose is too low to stimulate the body to produce sufficient antibodies, which in turn cannot produce effective immunity. Improper vaccination route, such as subcutaneous injection in the neck where the injection site is too close to the head, can cause inflammatory reactions; When injecting into the chest muscles, inserting the needle too deeply can easily puncture the chest and abdominal cavity; When injecting into the leg muscles, hitting the inner leg muscles can easily damage the leg nerves; Excessive handling during eye and nose drops can result in vaccines being directly thrown out of the nostrils of poultry, leading to missed doses in animals; When drinking water for immunization, incomplete disinfection of drinking water equipment can affect vaccine efficacy and lead to immunization failure. Inactivated vaccines should be warmed up before use (soaked in a 37 ℃ water bath for 30 minutes), as direct injection can cause significant stress reactions. In addition, incomplete or improper disinfection of immune equipment such as syringes and needles can lead to exogenous bacterial contamination, thereby affecting the immune efficacy of vaccines.

3、 Disease factors

The disease factors that affect the immune response of vaccines include immunosuppressive diseases, pathogen mutations, etc.

The mutation of local epidemic strains or the mismatch of vaccine strains can directly lead to the inability of the antibodies produced by our vaccines against this pathogen to effectively kill the pathogen, resulting in immune failure. Immunosuppressive diseases can damage the central or peripheral immune organs of animal bodies (such as spleen, lymph nodes, thymus, etc.), hinder the production of lymphocytes, reduce or prevent the production of immunoglobulin, leading to immune response dysfunction, inability to produce effective neutralizing antibodies, and thus affecting the effectiveness of vaccine immunity. Common immunosuppressive diseases in poultry in clinical practice include Marek's disease, avian leukemia, reticuloendothelial hyperplasia, infectious bursal disease, infectious anemia, reovirus infection, coccidiosis, fungal toxin poisoning, etc.

4、 Animal intrinsic factors

The health status and genetic factors of animals themselves can also affect the effectiveness of vaccine immunization.

The health status of animals themselves can be divided into healthy state, sub healthy state, pre disease state, and disease onset state. The levels of antibodies produced by animal bodies to the same antigen stimulation vary under different health conditions, and only by keeping the poultry population in optimal health can a better immune response be produced.

Genetic factors (such as variety, age, etc.) also have a certain degree of influence on the immune efficacy of vaccines. Different varieties, ages, and even individuals of the same variety may have different responses to the same vaccine due to their own conditions.

5、 Immune program factors

Unreasonable immune programs can affect the immune response level of animal organisms. The development of a scientifically reasonable immunization program does not necessarily mean that more types of vaccines are better. It needs to be tailored to the actual situation of the field. In addition, it should be formulated based on the local epidemic situation, breeding varieties, age, production status, actual situation of the breeding farm, and monitoring of maternal antibodies.

The impact of maternal antibodies: Maternal antibodies are a double-edged sword, not only protecting newborn animals from disease infections, but also interfering with their vaccine immunity [5] [6]. If the breeder fails to monitor the maternal antibodies of the poultry in their house, resulting in premature or delayed vaccination, it will affect the immunization effect of the vaccine: if the vaccine is administered too early, the maternal antibody titer will still be at a high level, and the vaccinated vaccine will be neutralized by the maternal antibodies, causing immunization failure; Late vaccination can easily lead to an immune blank period, posing a risk of infection to the poultry population. Therefore, vaccination can only be administered after the maternal antibodies have subsided to a certain level.

Mutual interference between immune systems: When two or more vaccines are administered simultaneously to livestock and poultry, the body's immune cells may experience immune tolerance, resulting in a decrease in the immune response ability to one of the antigens, which affects the effectiveness of vaccine immunity [7]. Therefore, in order to ensure immune efficacy, it is best to use single valent vaccines for immunization against locally prevalent diseases.

6、 Environmental and management factors

Getting vaccinated in adverse weather conditions, such as high temperatures, cold temperatures, rainy weather, excessive humidity, etc., can also affect the immunization effectiveness of the vaccine.

Excessive temperature and humidity, poor ventilation, high feeding density, and poor environmental hygiene are not suitable for the growth of poultry flocks and are also not conducive to immunization. Improper feeding and management can easily trigger stress reactions in poultry flocks. There are a large number of pathogenic microorganisms in the environment, and animals are highly susceptible to infection. If vaccinated in this situation, it will affect the effectiveness of the vaccine and lead to immune failure. In addition, improper use of disinfectants two days before and after vaccine immunization can have an impact on vaccine efficacy and affect the effectiveness of vaccine immunization.

7、 Nutritional factors

Malnutrition or excess can lead to damage to immune organs, affecting the effectiveness of immunization. The decline in the body's immune response ability is influenced by vitamins, amino acids, and certain trace elements. For example, vitamin E can promote the production of ND antibodies [8]. In addition, the deterioration of feed materials and feeding with feed containing mycotoxins can lead to thymic lymphatic atrophy and decreased macrophage phagocytic ability, causing immune suppression.

8、 Drug factors

Drugs achieve the goal of treating and preventing diseases by inhibiting and killing pathogens. Some drugs can inhibit the proliferation of immune cells, thereby affecting the production of vaccine antibody levels. Generally speaking, antibiotics and other antibacterial drugs should not be used within 3 days before and after immunization with live bacterial vaccines, otherwise it will lead to immune failure. Antiviral drugs can affect the immune efficacy of live viral vaccines, so antiviral drugs should not be used when receiving live viral vaccines. The use of immunosuppressive drugs during immunization can lead to a decrease in the body's immune cells, which in turn affects the body's immune response.

reference:

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