Investigating Vaccine Failure

Whenever a vaccine fails we blame the quality of vaccine. A proper investigation is needed to understand and minimise the vaccine failures.There are many factors that can lead to vaccine failure. Vaccine is like life insurance. Most people have lifeinsurance, but few hope to have to use it anytime soon. Similarly in a poultry the objective should be disease prevention (through effective management and nutrition). However, if there is unavoidable lapses in management and nutrition, the vaccination program (insurance) needs to be adequate and effective to minimise resulting losses. A thorough understanding of the causes of vaccine failure will help prevent such losses in the Poultry.

Newcastle disease (ND), infectious bursal disease (IBD), fowl pox, Marek’s disease, infectious bronchitis (IB), avian influenza, hydropericardium syndrome, etc are common diseases of commercial and rural poultry farming. It is very common to see an outbreak in vaccinated flocks. Proper understanding about the vaccine failure will help one to take good prophylactic measures to prevent disease outbreak. 

Vaccine failure is the consequence of the inability of the chicken to develop adequate immunity after immunization or susceptibility of bird to field outbreak after administration of vaccine

Why Vaccine fails?

The causes of vaccine failure can be categorized into two major factors: Vaccine related factors and Host related factors.

1.Vaccine related factors

It is important to have protective vaccine antigen to prouce adequate antibodies against field pathogen. Vaccine related factors leading to vaccine failure could be as follows. 

Inadequte number of antigens

 The number of antigens in the vaccine may be low which results in low antibody production hence low immunity level in birds. Lack of standard procedures and inadequate production facility is responsible for non potent vaccine. One should purchase the vaccine from the manufacturer with good manufacturing facility

Using non specific antigen strain.

 Strains of viruses differ from area to area. Some of the serotypes are prevalent in one area and some are in other. Vaccine made with serotype which is different from field strain will not produce adequate protection against field strain. Local serotypes and locally isolated antigens are considered the most suitable immunogens for formulating vaccines. 

Inappropriate storage temperature

Vaccine storage is very important as inappropriate storage may harm the antigens and may lead to vaccine failure. This is probably biggest factor contributing to vaccine failure in developing countries. There could be lapses in maintaining appropriate temperature at different levels like manufacturer, transportation, distributor and farm level. It is very important to identify and procure the vaccine from reliable distributor and manufacturer.

Direct sunlight exposure

Exposure of vaccine to direct sunlight is harmful for antigens present in the vial. UV rays present in sunlight may even kill the antigens. Vaccine exposed to sunlight may not work. It is important to protect the vaccine from sunlight exposure.

Expired vaccines

There is certain shelf life for every vaccine beyond which it will not provide protection. One must check expiry date on vaccine everytime one uses the vaccine. 

Mutation of viruses

Some viruses keep on changing their structure and internal biochemistry. It is very tough to formulate the vaccine for such viruses. 

1.Host related factors

Even if all vaccine related factors are perfect then also there are chances of vaccine failure due to host related factors. Which are as follows.

Stress

Managemental and environmental factors may lead to stress in Poultry birds. Birds in stress may not develop proper protection after the vaccination. There could be number of factors responsible for stress like extreme weather, transportation, handling , poor housing conditions and nutritional deficiencies etc. One need to have thorough knowledge about Poultry farm management to minimise the stress. 

Sick Birds

Only healthy birds should be vaccinated. Vaccinating sick birds may cause post vaccination reaction and further morbidity or mortality may increase. One should investigate the reason for sickness and treat the bird prior to vaccination. Vaccination should be done only when birds are healthy.  

Maternal derived antibodies

In certain viral diseases antibodies are transmitted from parent stocks through eggs. In such cases antigens inoculated will be neutralized by the maternal derived antibodies and birds will not be protected. One should take an advice from a consultant regarding scheduling of the vaccine to avoid interference of maternal derived antibodies.

Inappropriate route of administration

Every vaccine has a  specific route of administration e.g. Oral, subcutaneous S/C , intramuscular I/M , wing web (W/W), drinking water (D/W), eye dropping (E/D), spray, etc. Vaccine should be administered as per recommended route. Inappropriate route of administration may lead to vaccine failure. 

Inadequate dosage

Underdosing the vaccine may lead to vaccine failure. Underdosing may lead to poor protective titres and overdosing may lead to undesirable post vaccination reactions.One should follow the dosage recommendation strictly for development of  proper immunity in the birds.

Unsuitable water

There are some live vaccines which are given to birds through drinking water. If water is chlorinated or if water is having antimicrobial contents the vaccine may fail. One should use chlorine and antimicrobial content free water for vaccination.

No booster dose

Some vaccines need booster dose for proper protection. If booster dose is not given then there will be inadequate immune response for that vaccine. One should be aware about the scheduling of the vaccine.

Inappropriate vaccination schedule

Vaccine should be done strictly as per the vaccine schedule prescribed by the Veterinary Doctor. Wrong scheduling may lead to vaccine failure.   

Summary

After thoroughly understanding about the reasons of vaccine failure one can minimise the chances of vaccine failure. One should not overlook the good management practices and good nutrition program for prevention of diseases. Poor management and poor nutrition minimise the chances of vaccine success.