Martin,
I should have added in my previous post that the use of substandard vaccine is to be deplored and that one of the reasons for doing post-vaccination surveillance is to ensure that the vaccine being used is stimulating the immune system of vaccinated poultry.
However, if a chicken with poor immunity (i.e. one vaccinated with a sub-standard vaccine) is exposed to a current Asian H5N1 virus it is extremely unlikely to become a carrier – instead it will almost certainly die (as occurred with the poultry given poor quality vaccine in Liaoning Province). Poor quality vaccines may give farmers a false sense of security but these poorly protected flocks shouldn’t spread any more virus than fully susceptible non-vaccinated flocks exposed to a similar virus.
There has been a major shift in thinking on use of vaccines for AI recently. Until the Hong Kong experience in 2002-03 (when it was apparent that the virus was endemic in the region and repeated culling was not sustainable) no one had really tried systematic vaccination against highly pathogenic avian influenza. It worked.
The earlier policy on vaccination from international authorities were based on previous situations where the disease was newly diagnosed and recently introduced, not a situation where the virus was endemic.
On Peter Singer’s article, it is worth noting that the vast majority of cases of HPAI now are in the backyard and scavenging/free range sector not the large “industrial” farms. In fact well managed large farms pose a much lower risk than the non-biosecure backyard farms because they can practice good biosecurity.
Groups and indviduals who oppose industrial farming are using the current outbreaks of avian influenza to discredit this type of farming. I will not go into the merits or otherwise of their case re intensive farming but using avian influenza to attack this practice is lousy science and opportunisitic.
Les Sims