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Vaccination failure

By Dr Arthur Wellington on behalf of the Pig Vet Society

Vaccination failure is usually reported by farmers who have vaccinated their animals and in their own words “It did not work”.

Nothing in biology is one hundred percent effective and this is also true for vaccination. Failure of the effect of a vaccine can be discussed under the following three headings:

1. The vaccine itself
2. The administration of the vaccine
3. The status of the animal being vaccinated.

1. The vaccine itself

a. Vaccines are generally labile and thus can be easily damaged. Damage can be caused by heat, deep freezing, continuous removal and replacing in the refrigerator, sunlight, etc. In other words, the cold chain has been broken. In the past it was found that one of the reasons for this damage is the transport of the vaccine either in the glove box or boot of the vehicle.

b. The use of expired vaccines. Check the expiry date of the vaccine. Under no circumstances should an expired vaccine be used.

c. The use of an incorrect vaccine. In this case the farmer has made a wrong diagnosis. Rather consult your veterinarian in order to ensure that the correct diagnosis/information is given and the correct vaccine is used.

d. Strains (serotypes) which are not in the multivalent vaccine. In the case where there are numerous strains of a bacteria/virus which may cause disease, not all the strains are included in the vaccine. Different strains also may not cross protect against each other. The animal may thus not be protected against that strain not included in the vaccine. 

2. The administration of the vaccine

a. Do not give antibiotics simultaneously or shortly before or after vaccination. This may result in a live organism in a live vaccine and/or result in nil/very little immune response being produced.

b. Transfer of a disease, for which you are not vaccinating, during the vaccination procedure. This will take place if one or more animals have the disease, as yet undiagnosed, and the disease is transferred mechanically from animal to animal by the needle. In this case the farmer may incorrectly blame the vaccine as containing the disease organism.     

c. Vaccinating during disease incubation. Should you vaccinate during this period then the pig will show signs of the disease before the vaccine takes effect.

d. Failure to follow up the initial vaccination with boosters. These boosters are in the case of killed (inactivated) vaccines essential for the development of good immunity. The manufacturer of the vaccine will recommend as to when such a booster should be given.

3. Health of the animal

a. Animals that are in poor health due to malnutrition, mineral or vitamin deficiency, heavy parasite infestation or chronic diseases will not respond well to vaccination.

b. Passive immunity. Antibodies are transferred either prior to birth or predominantly via the colostrum from the vaccinated sow to the piglet. This transfer provides the piglet with passive or maternal immunity. Should a vaccine be given during the period of maternal immunity then this will prevent the development of active immunity in the piglet. Please consult your veterinarian as to how long such maternal immunity lasts and when is the best time to vaccinate such piglets.

c. Herd response to vaccination. In the population of animals the ability to development an immune response follows a normal distribution curve. Nothing in biology is one hundred percent effective and that is also true of vaccination.

There are several reasons for the poor response seen in the few animals seen at the “tail” (A) of this normal distribution. The size of this tail will vary, as discussed earlier, with the nature of the antigen used, the health and immune competence of the individual, the presence of maternally derived antibody, failures in administration and poor storage.

Conclusion

•  It is of the utmost importance that the correct vaccination programme be drawn up in consultation with your veterinarian.

•  Maintain the cold chain for the storage of the vaccine.

•  READ the package insert of the vaccine before use.