We are seeing plenty of cases of vaccine failure as outbreaks of velogenic Newcastle disease and Infectious Bronchitis which are reported in in vaccinated flocks. How do you think should one investigate failures? If outbreaks occur in presence of sufficient antibody titres. Will virus isolation and sero-neutralization in ovo be enough. Or should one do challenge tests in vaccinated birds?
Any suggestions?
vaccine vailure in the presence of "sufficient" antibody titres would probably indicate lack of neutralizing antibodies. This could be due to inefficient induction by the vaccine itself or by occurence of escape mutants / new strains. Thus, the first thing to check would be to sequence the viruses from the infected animals. The next task would be to validate the preence and titer of neutralizing antibodies. In more complicated situations vaccine failure may be due to coinfections which may be much more severe and where the vaccine doesnt provide enough protection.
i will add few points, here in Pakistan, the two most frequently used vaccines are N.D and I.B, i have not seen any farm (broiler or layer, small open sheds or environmental controlled shed) where these vaccines are not use. So the resistance against vaccine or stain mutation might the reason behind the failure. that is why sequencing must be practiced when ever any failure occure.
Markus and Sajid both provided excellent possibilities. I would add that the development stage when the failure occurs could also be important. If the vaccine is still in nonclinical testing, then failure could simply be due to the choice of animal model. It is known that some vaccines do not elicit neutralizing antibodies in certain species (e.g.., mice) and therefore appear not to be efficacious in a challenge study. But, when used in another species (e.g., nonhuman primates), the vaccine is quite effective due to the presence of antibodies. So, it's important to think carefully of the animal model.
What percentage of animals that have not adequately responded to the vaccine ?
is that there was no concomittentes infections during administration of the vaccine?
The pesonnel in charge of vaccination is -it used to this mode of vaccination?
Cold chain -it is well respected ?
Would you have vials of these vaccine for a possible control by laboratory .
Agreed with points mentioned.Vaccine quality may be an issue and should be checked. Functional, eg neutralisation, assays should be used. Reliance should not be placed on ELISA. Prevalent virus strains should be checked for genetic change. Challenge tests are the gold standard but require time and adequate facilities and would probably be done as a last resort.
Is it true 'vaccine failure' or is it that some animals have not responded as they should? I find that in the vet world most investigations are the latter and wholesale lack of efficacy of a batch is very rare. I have a decision tree that I use for investigating likely causes of 'poor responsiveness'. You must also consider the health status of the animal at time of vaccination and time of challenge.
the possibility of vaccine failure is not far away from the fact mentioned by Mahfoud, howerver, in addition, failure from poor handling of the vaccine and inadequate viral titre antigens to stimulate enough antibodies that can confer immunity may also be a major cause of vaccine failure.
I would normally be wanting to take first and second bloods from at least 6 ideally 30 plus at least 10 days apart, ideally at time of vaccination and 2 to 3 weeks later. Then I would run those bloods for antibodies for a whole series of different pathogens depending on local known epidemiology. Need to check no other agent involved with an immunosuppressive effect or other effect. I have seen relatively hot ND vaccine cause severe respiratory problems due to mycoplasma (sero conversion demonstrated to Myc seen as well as ND)
Vaccine/vaccination failure could be multi-factorial, and for that reason you need to do thorough investigation by using an exclusion checklist. You can rank your list according to the most probable factor in your practice having a role in vaccine protection failure and excluding by using trial and error method.
The following are common factors responsible for vaccine failures in commercial poultry.
Vaccination Program
Administration and Handling of the Vaccine
Vaccine Administration Deficiencies
Maternal Antibodies
stress
Timing
Immunosuppression
Management Practices
Vaccine Quality
Vaccine modifications
Vaccine strain\serotype
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