CAUSES OF VACCINE FAILURE
Vaccination is the administration of antigenic material to stimulate the immune system to develop adaptive immunity to a pathogen, provided they are used at the proper time, age and method. Effective vaccine application is a crucial part of modern poultry production as diseases remain the greatest threat to the poultry industry and are responsible for very large economic loses to the farmers. Failure occurs when the birds do not develop adequate antibody titre. Factors responsible for vaccines failure are as follows;
High level of maternal antibodies in chicks. This can interfere with the multiplication of live vaccines thereby reducing the amount of immunity produced.
Stress which includes inadequate nutrition, environmental extremes (temperature and relative humidity), parasitism and other diseases may reduce the chicken’s ability to mount an immune response. Do not vaccinate until the birds are healthy.
Vaccines may not contain the proper strains or serotypes of organism required to stimulate protective immunity. Buy vaccine from a reliable source. Check vaccine for expiry date, do not use contaminated vaccine. Don’t use leftover vaccine.
Health status of the birds. They may already be incubating the disease at the time of vaccine administration, birds become diseased because time is needed for antibody production to begin and reach protective levels.
Also, birds already immunosuppressed with mareks, IBDV, secondary bacterial infection, or from consumption of feed with high levels of mycotoxins may result in the development of only limited protection. In case of worms, deworm birds before vaccination.
Poor cold chain maintainance. Bad electricity, frequent opening of refrigerator door and frozen vaccines. Transporting without cooler boxes and icepacks. Store vaccines between 20C-80C.
Improper Vaccine reconstitution. Proper timing after reconstitution is important. Monitor diluents temperature and quality, water should be free of heavy metals, chlorine, disinfectants and detergents. Only mix skimmed milk powder with water for treatment for live vaccines. Exposure to uv light (direct sunlight), time from re-suspension to use.
Improper Vaccine administration. Insufficient drinkers, ambient temperature, stability of water, equipment used for spraying, experience of vaccinator, vaccine loss due to settlement, evaporation and drift of the droplet, dropping of eyelid, closed eye, scratching eye, positioning of dropper, wrong inoculation, wrong positioning of needles, incorrect site of inoculation.
Environmental factor: poor ventilation or high ammonia level, dirty house.
Human factor: Bad handling of birds, rushed vaccination and missed birds. Vaccinator should follow biosecurity measures strictly. Improper disposal of vials and needles.