email from Ruth Watkins about DEFRA's reasons for rejecting H5N1 vaccination of healthy birdsreceived November 16 2007
"Currently available vaccines have disadvantages in that although they are able to reduce mortality, it is possible that some vaccinated birds would still be capable of transmitting the disease if they became infected whilst not displaying symptoms. This would increase the time taken to detect and eradicate the virus."
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.
ARCHIVE 2001 -2007
Fields of Fire witness accounts of 2001
Foot and Mouth policy 2001 - opinions
FMD Front Page Current
General Archive Page (new window)
FMD Front Page September 2005 - Dec 2005
Archive August 2007 Surrey outbreak - stage 1
Archive July 2007
Archive June 2007
Archive May 2007
Archive April 2007
Archive March 2007
Archive February 2007
Archive January 2007
Archive December 2006
Archive November 2006
Archive October 2006
Archive September 2006
Archive August 2006
Archive July 2006
Archive June 2006
Archive May 2006
Archive April 2006
Archive March 2006
Archive February 2006
Archive January 2006
FMD Front Page Oct 2004 - August 2005
General Front Page (includes other and related items)
Front Page Autumn 2004
Front Page Summer - October 2004
Warmwell front pages Spring 2004
Warmwell front pages Oct 03 - Jan 04
Warmwell front pages Sept 2002
Warmwell front pages August 2002
Warmwell front pages June / July 2002
Warmwell front pages - May / June 2002
Warmwell front pages - April / May 2002
Warmwell front pages - March / April 2002
Warmwell front pages - the earliest pages in 2001 - March 2002