I see they say that infection of some vaccinated birds without displaying symptoms whilst being infectious to other birds would delay eradication.
I think they are wrong if the whole flock is vaccinated.
If 3 weeks has passed since commencing the vaccine course (2 doses) (or the time stated by the manufacturers for full immunity) then there will be a solid immunity in the flock. We are not talking about vaccinating an already infected flock.
What if the vaccinated flock is then exposed (infected straw or something)?
Leaving sentinel unvaccinated birds in a flock is not a good idea, as if infected by the contaminated straw for example, these will shed a lot of virus. Vaccinated birds if infected will shed less virus and the infection will not progress through the flock because the other birds are vaccinated and have fully resopnded.
This is what happens in the papers displayed on Warmwell.
I think people get confused as to why vaccine works so well in birds (providing the H5 is a good match) compared to influenza vaccine in humans against our current circulating strains.
Firstly only a small proportion of the human population is vaccinated, not enough to make a difference to the circulation of current influenza strains and the exposure of vaccinees to high doses from acutely infected unvaccinated persons. By vaccinating the entire flock of poultry on is avoiding this situation.
Secondly we have infection with influenza throughout our lives, probably every 3 years or so. Our immune system ensures the virus drifts, and of course rarely there are the shifts when perhaps half the world's population gets infected in one year. Vaccination of infants, given 2 doses, is highly effective. When vaccine is given to adults and old people the vaccine may remind the immune system of previous infections with slightly different viruses with cross reactivity and the level of neutralising antibody to the vaccine strains may not therefore be all that could be desired (the concept of original sin). One might also be able to use stronger adjuvants in animals than are permitted in humans. In the case of domestic poultry it is unlikely they have had any prior influenza infection so with a well adjuvanted and primary course of 2 doses the poultry make a good protective immune response. (Their immune system is different from ours, the Bursa of Fabricius, and this may affect their immune resonse)
I do object to DEFRA's use of "protection" when they really mean noticing clinical disease at a stage when few birds have died from it.
yours sincerely
Ruth Watkins
Fields of Fire witness accounts of 2001