Farmers sometimes say “we vaccinated, but the birds still got sick.” In most cases the vaccine was good when it left the manufacturer. The failure happened somewhere along the way. Knowing the common causes helps you prevent them.
1. Storage and handling
Vaccine exposed to heat, sunlight or freezing loses its strength without any visible change. Mixed vaccine kept too long before use also weakens. Fix: strict 2–8°C storage, an ice box for transport, and use within the time on the leaflet.
2. Poor administration
- Chlorine or disinfectant in drinking water kills live vaccine.
- Too much water or too few drinkers — some birds never drink a full dose.
- Eye drops that fall off before being absorbed; injections given into the wrong site or missed.
- Spray droplets of the wrong size, or sprayers contaminated with disinfectant.
Fix: trained vaccinators, correct equipment, stabilisers in water, and supervision.
3. Wrong timing
High maternal antibodies can neutralise a live vaccine given too early. Vaccinating too late leaves a gap when field virus can infect the flock. Boosters missed in layers and breeders let immunity fall. Fix: a schedule planned for your flock and followed exactly.
4. Birds that cannot respond
A weakened immune system does not respond well to any vaccine. Common causes are early Gumboro infection, Marek's disease, chicken infectious anaemia, mycotoxins in feed, poor nutrition and heavy stress. Fix: control these underlying problems, and test feed for mycotoxins.
5. Birds already infected
Vaccination prevents disease; it cannot cure birds already incubating infection. Vaccinating in the middle of an outbreak may not stop losses. Fix: vaccinate on schedule, before the risk period.
6. Wrong vaccine for the challenge
Some diseases, such as infectious bronchitis, exist in several types (strains). A vaccine may not fully protect against a different field strain. Very high field challenge may also overwhelm a mild vaccine. Fix: laboratory diagnosis and a vaccine choice based on what is present in your area.
Quick checklist
- Vaccine within expiry, stored 2–8°C, temperature log kept
- No chlorine or disinfectant in water around vaccination
- Correct dose per bird and correct route
- Schedule planned with a vet and recorded
- Batch numbers and dates written in the farm register
- Feed quality and mycotoxins checked