In my avian practice that spans over 20 years, I have occasionally been confronted by farmers who complain that they vaccinated their flocks, yet they came down with the disease. Today, I will highlight why vaccination may fail. Vaccination is the physical administration of an antigen (vaccine) into a healthy bird whereas immunisation is whereby the antigen administered stimulates production of antibodies and provides immunity against diseases. So, a farmer can physically administer vaccine, but birds fail to be immunised due to several factors.
Always check the date of manufacture and expiry date of the vaccines before buying. Do not use expired vaccines, keep a record of vaccine type, expiry date and batch number on a health card. Expired vaccines are a waste of your time and money.
Poor vaccine handling and storage
The responsibility of maintaining the right conditions for vaccine storage rests in the Vet shop and partly the farmer soon after buying prior to vaccine application. Live vaccines should be stored at between 2-80C in a fridge and regularly monitored using a minimum-maximum thermometer. Farmers can use cool packs, well insulated cool box or flasks to keep the vaccines cool during transport. If this cold chain is not maintained, the vaccines will be rendered useless.
Poor water quality
The ideal water for vaccination must be free from chemicals, minerals, vitamins, disinfectant and chlorine. These chemicals tend to denature live vaccines and render them inactive. They must be removed 48 hours before vaccination. Boiling water a day before can help soften it and remove chlorine. Alternatively treat with skimmed milk powder at rate of 2g per litre or use a stabiliser like Cevamune, Aviblue at 1 tablet in 100 litres of water.
Do not vaccinate sick and unhealthy flock. If you do, the bird’s immune system may not respond positively by producing enough protective antibodies and the exercise will be futile. Any flock showing unprecedented mortality should be treated first before any vaccination. Vaccination schedules are not cast in stone, you can do it a week late when the flocks are in good health.
Poor vaccine preparation
Establish how much water is needed to mix vaccines for your birds at the specific age and duration. Vaccine water must be calculated to be consumed within one hour. The water volume is calculated like this: (Age in days x No of birds x1.1)/1,000 for birds not older than 40 days. The vaccine vial should be opened in water, then starred and be given immediately. Vaccines must be given according to the age, type of bird and by the local veterinarian registered by recognised veterinary Board. Excess vaccine water lasting more than two hours may lose their efficacy and if you give less vaccine water, some birds may not consume and become vulnerable to infection.
Poor vaccine intake
Controlling vaccine administration is key to obtaining the best vaccine response. Add a dye or colorant to the vaccine water prior to vaccination. Hours after vaccination, check randomly about 2 per cent of the birds in different areas of the house the presence of dye in the tongues of these birds. If the signs of intake are negative, repeat the vaccination because if there is no vaccine intake, there will be no immunisation.
After vaccination, continue with clean water without addition of chemicals like chlorine until the following day. Give multivitamins for the next three days as an antistressor and to prevent undesirable reactions. In cold climate, it is good to increase the ambient temperature in the house to reduce adverse reactions.