The essence of vaccination is the administration of optimal and safe amounts of antigens to stimulate immune response in a host against viral, bacterial and protozoal diseases. Vaccination however does not necessarily guarantee protection. Many other factors combine to produce a successful vaccination. It should be noted from the onset that vaccines or the act of vaccination do not produce the immunity that protects the chicken, rather it is the chicken’s immune system that provokes the immune response, which ultimately confers the needed protection. A successful vaccination will ultimately elicit optimal and strong immune response.

 GENERAL PRINCIPLES OF VACCINATION: To produce optimal immune response, a functional vaccination program should be developed based on the knowledge of diseases prevalent in an area, risk of exposure, immune status of parent stocks, cost of acquisition and administration of vaccines, flock placement programs, availability of specific vaccines and cost benefit ratios associated with vaccination taking into account the risk of infection and financial loses from disease.

PRECAUTIONARY MEASURES:

• Do not vaccinate birds during stress period especially few days before or after debeaking, transfer and grading. These produce stress conditions that may lower the immunity of birds.
• Do not vaccinate birds during extreme hot weather. Heat stress may lower the bird’s immunity, while high environmental temperature may destroy the efficacy vaccine. Vaccination should be carried out during the cooler periods of the day Morning and evening).
• Avoid using metal drinkers and containers for mixing of vaccines. Metals may inactivate live vaccines offered through the drinking water. Aluminum and brass containers are equally not recommended since they also known to have high inactivation properties. Plastic containers should be used.
• Use clean equipment, drinkers and sterile syringes.
• Do not use chemical disinfectants to clean utensils before vaccination because the residues of these chemicals may inactivate the vaccines. The utensils should be rinsed with fresh water.
• Always use sterile diluents preferably of the same company for reconstitution of injectable vaccines, since some diluents may contain more than optimal levels of dye, which act as sterilize for the diluent but at same time, may inactive the vaccine.
• Do not use chlorinated water for vaccine dilution since the chlorine will destroy the vaccine. Suspect municipal tap water should be made to stand in an open plastic container for at least two days to allow dissolved chlorine to escapes.
• Reconstituted vaccine should be used within one to two hours. Delays in utilization either from the farmer by the birds may lead to decreases in vaccine efficacy.
• In areas having established high salt concentration in water, the preferred route of vaccination are injection or eye, nose and mouth dropping.
• Addition of skim milk to the water used for oral vaccination aid in optimal distribution and stabilization of vaccines. In case milk. Lower limit of skim milk per liter is fixed but there is no upper limit, the higher the milk concentration the better the suspension of vaccine in drinking water.
• The birds should be made to consume the reconstituted vaccine within one hour of its introduction, taking into consideration the temperature of the pen and feeding time.
• Do not exposure reconstituted vaccine to heat, sunrays, high room temperature, brooding house temperature.
• Do not open the lid of the vaccine vial in the open since the vial is sealed under negative pressured and will suck in contaminated air. Use sterile disposable syringe to reconstitute the vaccine or open the vial inside water.
• Avoid reused or disinfected syringes and needles. Always use wide bore needles for vaccine suction or dilution since narrow bore needle may retain some cell culture vaccines, thus making for non uniform mixing.

 ROUTES OF VACCINE ADMINISTRATION:

Various methods of administrating vaccines are used commercially in Nigeria. These include;

Intranasal: This is carried out either with special equipment or by dipping the beak into the reconstituted vaccine up to the nares. In birds, the nose, mouth and tear duct open into the mouth, Therefore, any of these routes will give the similar result.

Intra-ocular: This is a very popular route of vaccination. Intra-ocular and intranasal routes are suitable for hatchery administration and during brooding of chicks. In Nigeria eyedroppers are usually 40ml for 1000 birds. The reconstituted vaccine should be used within a specified time since too holding the dropper for too long may cause inactivation of the vaccine. Again, contaminated diluents or vaccines may cause infection in the eyes or block the tear duct or drooling of water from the eye used for vaccination.

Drinking Water: This corresponds to oral and intranasal administration. Drinking water administration is popular among large and small-scale farmers in Nigeria, and can be carried out at low cost. It is however of limited effectiveness against some infections.

Injection: This could be given through subcutaneous or intra-muscular route, depending on the type of vaccine and instruction of the manufacturer. Subcutaneous route could be used to administer either live or inactivated emulsion vaccines to rearing stocks and breeders.

Post-Hatch Spray Vaccination: This is done in cabinets for mass-administration of aerosol vaccines to day old chicks. This is mostly employed for Newcastle disease and infectious bronchitis vaccination on day one in the hatchery or farm.

Wing-web Stab: This method is used to administer fowl pox vaccine or other live vaccines directly to each bird. Care must be taken to ensure that the eye of the needle carried the appropriate amount vaccine each time it is dipped into the vaccination bottle.

Aerosol Administration: This involves using a knapsack or electric sprayer to deliver vaccines to flocks as a coarse spray.

 CAUSES VACCINE FAILURE:

Use of Expired Vaccine: Vaccines may expired through many ways, the most common being expiration in storage as a result of poor sales. The cold chain may also be broken as a result of poor refrigeration storage arising from irregular electricity supply.

Improper storage of vaccines: This is the most common cause of vaccine failure. This may arise from poor handling during transportation from market to farm or from manufacturer to distributor. Irregular electricity supply, poor refrigeration, storage in deep freezers, prolonged exposure to sunlight among others can also compromise the storage and efficacy of a vaccine. Icebox, coolers or thermos flask should always be used in transporting vaccines rather than and thin translucent polyethylene shopping bags.

Genetic Resistance : Genetic make up varies from bird to bird and its structure dictates whether a bird will ultimately respond to an antigen. It is possible for the immune system of some birds not to mount enough immunological response to a particular vaccine. As a result, that strain of bird may be less protected by the vaccine and thus become more susceptible the disease condition.

Health Status Of The Flock: Infectious agents such as Chicken Anemia Agent, Gumboro Disease Virus, Marek’s Disease Virus, Salmonella and Mycoplasma etc. may cause varying degree negative immunomodulation, which consequently may lead to vaccine failure or adverse reaction in the face of these disease.

Immuno-suppression Due to Drugs: Continuous administration of Immuno-suppressive drugs such as chloramphenicol, furazolidone may cause poor immunity development and consequently poor immune response after vaccination.

Mycotoxins: Presence of mycotoxin in the feed has negative affect on vaccine response. Mycotoxin reduces host immunity directly by reducing macrophage-engulfing ability and by reducing the activity of lymphocytes in immunity development. Mycotoxin indirectly affect birds by producing steroids from the adrenal glands, which decrease lymphocyte numbers while increasing hetrophils thereby compromising their immune system.

Water Deprivation and Heat Stress: Water deprivation will usually lead to heat stress, which in turn cause increased production of steroids and consequently decrease the lymphocytes ability to produce antibodies. Dehydrated and heat stressed birds are commonly susceptible to colisepticemia and other diseases.

Cold and High Density Stress: These social stress factors like heat stress decrease the immunity by decreasing the number of lymphocyte responsible for antibodies production.

Poor Nutrition: Prolonged protein deficiency in the diet may hurt immune response since antibodies are made up of amino acids. Poor protein nutrition will usually lead to problems with metabolism, protein synthesis and immunity.

High Ammonia Concentration: When ammonia levels are high in the pen, it hinders the birds ability to produce local immunity since the epithelial cells linings the mucosa of the birds are destroyed. In the absence of the local immunity the bird becomes susceptible to viral diseases particularly those that proliferates in the respiratory tract. Ammonia concentration above 100 ppm is always associated with respiratory disease. Since the ammonia is a water-soluble gas, one can easily feel ammonia as it dissolves in lachrymal secretion of the eyes.

Administration of Poor Quality Water: Poor quality water, especially those having high salt concentrations affect the efficacy of vaccines diluted in them.

Maternal Antibodies: High maternal antibodies sometimes inhibit the chicken immune response during early vaccination. High levels of maternal antibodies against infectious agent such as Gumboro virus play a role in neutralizing the vaccinal antigen thus making the vaccine less effective. In addition to this when high titer vaccine is used during early vaccination, the circulating maternal antibodies are also destroyed leaving the bird exposed to field challenge.

Presence of Variants in the Field: It has been observed that when new disease agent variants emerge, the classical vaccines may no longer be effective to control the disease.

Poor Antigenicity of Vaccines: Live vaccines must be applied at a level slightly above the minimum infective dose. After the live virus has been applied the bird serves as a virus production site. The bird becomes the medium in which the initial dose of vaccine can multiply to a level, which will stimulate a proper immune response. When in doubt about the potency of a vaccine, contact well equiped Laboratories. Inactivated vaccines should contain sufficient amount of antigen to stimulate an immune response when applied to the bird since there is no multiplication of the virus or bacteria in the bird.

Interference: Do not give live respiratory vaccines (IB, ND, ILT) within 3 to 4 days if not combined by the manufacturer in licensed combination. Reaction may be too great or response to the later vaccine may be compromised due to interference. This is also true in case of ND and AI vaccines. Do ND vaccination earlier and than proceed to AI vaccination.

Geonetics: This simply means the geographical influence on the genetics of local poultry population. Geonetical influence may affect the ultimate response of birds to vaccine under indigenous environments and may result in vaccine failure.

VACCINATION REACTION:

Adverse vaccine reaction does not serve a useful purpose and should be prevented at all times. Several factors can cause vaccine reaction to occur. These include; Chick quality, level of maternal antibodies, vaccine strain, dose of vaccine used, route of application, timing of vaccination, immune suppression, house sanitation, down time, water, litter and air quality.