Email received from Dr Ruth Watkins, Feb 19 2007
There is a great reluctance on the part of British intensive poultry farmers to contemplate vaccinating millions of birds. There is a reluctance to vaccinate in the UK on any count - and of course a history of persons vilifying vaccines. I hear that in Holland supermarkets have been unwilling to market eggs from vaccinated birds - so that must be one of the reasons vaccination has not been taken up by many free range producers. I suspect the supermarkets will make mayhem here as well.
Vaccination does not change the actual virus from a hare to a tortoise but the virus shed, if any, from an infected vaccinated animal would have all the properties of the wild virus (e.g. in the case of the highly pathogenic H5N1 it is highly infectious to non-immune poultry, (possibly excepting ducks who, although they may become infected, may not become ill and die as a result of infection), and just as lethal as before with the same short incubation period and swiftly progressing mortal illness). Hence the EU proposal to place unvaccinated (non-immune) sentinel poultry in a vaccinated flock as these would pick up any infection in the flock and fall ill and die.
The question about avian influenza vaccination virus preparations is: Are they protective against the current strain of H5N1? That is, do the vaccines raise protective immunity to the 2007 H5N1 Qinghai related strain currently in Europe? As the Haemagglutinin of viruses can be sequenced within days, the changes in the antigenicity of the H5 molecule of the H5N1 virus can be monitored. It can also be checked out in the laboratory by neutralisation assays.
I would have thought there is now good scientific evidence on the efficacy of H5 vaccines available to the EU with regard to current strains of the H5N1 virus.
Also, once poultry have had a full vaccination course, it is known when they have the full protection offered by the vaccine. I believe this is about 3 weeks after the first injection in a course of two (when inactivated, dead, virus vaccine). There should be information from Vietnam about vaccine efficacy in the field as well.
Where has the idea that there is long term circulation of H5N1 in a fully vaccinated flock in the absence of disease in the flock come from? What is the documentary evidence for it? I would have thought that if the virus were to continue to circulate in a fully vaccinated flock there would be the evidence of diseased birds as the immune cross reactivity of the vaccine virus would be so poor as to have failed to evoke the protective antibody, neutralising antibody to H5.
In fact in Vietnam they have had a long period of freedom from human cases of H5N1during their vaccination programme, presumably because the virus was not circulating in their domestic poultry. I have not read of their monitoring of H5N1 in the poultry during this period.
(Breakdown in vaccine protection in Vietnam can occur in various ways. They face two main difficulties. First to keep up the protection by vaccination, particularly of chicks and young birds coming into the vaccinated flocks. Secondly there is the continuous threat of a breach of border security by the poultry smugglers from China who can introduce H5N1 strains circulating in Southern China into Vietnam by bringing in unvaccinated as well as infected birds. This is different from the spread by wild infected birds that could also occur, from South CHina into Vietnam. This latter situation is exactly what the vaccination programme of the flocks in Vietnam is designed to protect against.
I would like to know the reason for the recent outbreaks they have had in one or two regions of Vietnam. How have fully vaccinated flocks fared in those regions? How does the virus isolated match up with the vaccine virus? I have looked at the ProMed reports on the recurrence of H5N1 in late 2006 and 2007 in Vietnam
There are a series of short reports on Promed and I feel that what I can glean from them is summarized above. This supports my assertions I feel. They have suspected H5N1 infection of humans in several instances but infection has not been confirmed. They have had no deaths since November 2005, and I presume also no further confirmed cases in humans either. That is a tremendous record when you consider Indonesia or Egypt for instance. )
- Only some localities have been affected, for instance the Mekong delta which is on the border with China. They do mention that one of the localities has a border with China where they cannot control the movement of poultry.
- A flock of infected ducks was cited in the Mekong Delta that had not been vaccinated. They were said to be asymptomatic, but then refernce is made to sick ducklings in another posting.
- Culling of all except vaccinated birds is advocated in one locality.
- More money has been forthcoming from the World Bank. Perhaps to help them with their vaccination programme which is to be stepped up which they refer to in one of the postings.
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