Estimated reading time: 7 minutes
- The purpose of a vaccine is to expose healthy animals to particular disease-causing organisms in a bid to develop immunity against a disease to which these animals might be exposed at a later stage.
- It sometimes happens that vaccinated animals contract or die from a disease against which they’ve been vaccinated, leaving producers wondering why the vaccine was not effective.
- Firstly, it is crucial to accurately diagnose the cattle that are sick or have died.
- The next step is to check the livestock producer’s records to verify the dates on which the animals in question were vaccinated and the booster doses administered.
- Vaccination simply entails buying a vaccine and administering it in the hope that the disease for which the vaccine is administered will be prevented.
The purpose of a vaccine is to expose healthy animals to particular disease-causing organisms in a bid to develop immunity against a disease to which these animals might be exposed at a later stage.
It sometimes happens that vaccinated animals contract or die from a disease against which they’ve been vaccinated, leaving producers wondering why the vaccine was not effective. Being a consultant, I’m often asked to investigate cases of disease or mortality among livestock that, according to the producer, were indeed vaccinated.
The following are a few examples of my own findings from cases I’ve investigated, as well as the methodology followed during such an investigation.
The correct diagnosis
Firstly, it is crucial to accurately diagnose the cattle that are sick or have died. Time and again I’ve found the cause of death to be entirely something different from the disease the producer initially suspected as being the reason for animals dying. There are cases of cattle dying overnight. In one such instance the producer suspected blackleg, against which the cattle was vaccinated, when in fact Asiatic redwater was to blame.
In another case the producer thought pulpy kidney, also against which the flock had been vaccinated, was the reason for sudden overnight mortalities among his sheep. However, the post mortem revealed that severe wireworm infection was to blame for the deaths. Such high infection loads can lead to animals dying very suddenly, and without other typical disease signs such as bottle jaw being present.
So, before investigating the reason for a vaccine’s supposed failure, the first step is to confirm what caused the illness or death.
Read more about Principles of a vaccination programme for cattle.
Health records
The next step is to check the livestock producer’s records to verify the dates on which the animals in question were vaccinated and the booster doses administered. Also vital are the animals’ nutritional status and stage of production at the time of vaccination.
This is where investigations often hit a snag, as some producers work from memory and cannot always remember when or with what animals were vaccinated. This is completely inadequate, and very often during such investigations it emerges that producers are uncertain as to whether the herd or flock has indeed been vaccinated, which vaccine was used (brand name, lot number, expiry date), and who administered it.
The biggest limitation when investigating the failure of a vaccine suspected is the availability of accurate records regarding the administration of that vaccine.
Vaccine administration
The third and most difficult factor to investigate is the administration of the vaccine. Are the people administering it sufficiently trained to consider all the factors playing a role in ensuring that animals are effectively vaccinated, the correct dose injected, and the cold chain maintained before and during vaccination?
Never assume that the correct process is being followed when administering a vaccine. This management task requires close monitoring and often also corrective or advance training of the people performing the vaccination.
Practical implementation
The following is a brief synopsis of the tasks involved in ensuring that the process is managed correctly. Table 1 provides a checklist producers or herd/flock veterinarians can use to best evaluate the vaccination process; the producer/veterinarian must also spend a day in the field with the team when animals are being vaccinated. It can also serve as a training session after the administering-of-vaccination procedure has been evaluated. The checklist can be used as is or adapted to each farm.
Table 1: Factors evaluated during vaccination.
| Equipment | Mark 0-5 |
| Functional table on which vaccines, coolers, syringes, and needles can be stored next to the crush so that equipment does not need to stand on the ground in the dust. | |
| A movable canopy or umbrella erected over the table so that equipment and vaccines are shielded from the sun. | |
| Coolers with ice packs for storing vaccines, as well as a cooler for storing syringes containing vaccine can be stored if the process is interrupted (>5 minutes) before vaccination can resume. | |
| Container with clean, sharp needles and a container for used needles. | |
| Clean, functional syringes suitable for administering the specific vaccine. | |
| If using an automatic syringe, are the barrel and connector connecting the syringe to the vaccine container intact and clean? Is the plastic needle sharp enough to only make a small hole in the cap of the container and not tear a large hole through which vaccine can leak or air sucked into the system? | |
| A working, functional crush in which animals can be handled safely and efficiently. | |
| No crowding of animals in the crush so that vaccination can proceed unhindered. | |
| Ease of access through the crush’s sides for the person administering the vaccine at the correct site on the animal. | |
| Vaccination technique | |
| Is the correct technique used to lift the skin to ensure the vaccine is administered subcutaneously? (Most vaccinations are administered subcutaneously.) | |
| Is the vaccine administered subcutaneously at the correct site? | |
| Is the person administering the vaccine ensuring that the full dose is administered with each vaccination, especially when using an automatic syringe? | |
| Is the person administering the vaccine making sure that the next dose of vaccine is loaded fully (full vaccine barrel) when using an automatic syringe? | |
| Can the applicator bleed air from the supply chamber or vaccine chamber if air enters the system when using an automatic syringe? | |
| In some cases one or two animals cannot be vaccinated (one might be lying down or on top of another). The person administering the vaccine will then finish vaccinating the other animals in the crush. Does this person return to these skipped animals and vaccinate them after a few animals have been let out of the crush? | |
| How many animals are vaccinated before using new needles? | |
| Are the number of animals being vaccinated recorded, or are they at least counted? | |
| Does the amount of vaccine used match the number of animals injected? (Further proof that each animal indeed received the designated vaccine dosage.) | |
| If the vaccination process is interrupted for a period of time (>5 minutes), is the full syringe stored in a cooler and kept out of the sun? |
These are only a few of the most important, practical factors that can be evaluated. In most cases, it becomes evident to the livestock producer and/or herd veterinarian that additional training and retraining is necessary for maintaining the cold chain during vaccination, improving the vaccination technique, and improving recordkeeping and the reconciliation of the number of animals vaccinated versus the number of doses administered.
Even the most basic recordkeeping can be used to verify whether all animals in the herd or flock were present and vaccinated, or that some animals were not. In the case of the latter, follow-up steps are necessary to ensure they are vaccinated.
Vaccination versus immunisation
Vaccination simply entails buying a vaccine and administering it in the hope that the disease for which the vaccine is administered will be prevented.
Immunisation is when vaccination is planned and done according to a vaccination plan drawn up in collaboration with the veterinarian. It considers the stage of production and nutritional status of the animals to be vaccinated. A vaccine can only stimulate the immune system to develop immunity if animals are vaccinated when they are in good physical condition and not under excessive stress.
Maintaining the cold chain before and during vaccination, ensuring that each animal is vaccinated, and keeping sound records serve as further confirmation that animals are indeed immunised. With planned and well-executed immunisation, the livestock producer can expect the vaccine to be effective and prevent the disease that animals are being vaccinated against.
For more information, contact Dr Danie Odendaal at vnet1@absamail.co.za. – Dr Danie Odendaal, director, Veterinarian Network
