Bird flu vaccination can ?worsen spread?

[MHSC]

<table border="0" cellpadding="0" cellspacing="0" width="480"><tbody><tr><td colspan="2" class="artHeadline">Bird flu vaccination can ?worsen spread?</td> </tr> <tr> <td colspan="2" height="1">

</td> </tr> <tr> <td class="artByline">JAMES MORGAN</td> <td class="artDate" align="right">August 17 2006</td> </tr> <tr> <td colspan="2">

</td> </tr> <tr> <td colspan="2"> Vaccinating poultry flocks against bird flu could make the spread of deadly strains such as H5N1 worse, Scottish scientists have found.

An Edinburgh University study concluded that, even though the available vaccines are effective on individual birds, the disease is likely to spread unless more than 95% of a flock has been protected.

The paper, published in the journal Nature, is the first to quantify how incomplete vaccination of flocks can contribute to the undetected spread of the disease.

In Vietnam, where 42 people have died of bird flu, mass vaccination of poultry has been successful in checking the spread of H5N1.

The Netherlands has already started unrolling a vaccination programme even though it has not yet been hit by H5N1.

But despite the Cellardyke swan, the UK authorities have ruled out a vaccination programme, on the grounds that it would disguise the spread of a much larger outbreak of H5N1.

"Silent spread" occurs because immunised birds can still catch and pass on avian flu, but without presenting any symptoms.

Therefore, as protection levels rise in a vaccinated flock, it becomes ever harder to detect the spread of avian flu, simply because fewer birds die. The result is increasing amounts of bird flu virus contaminating the birds' surroundings without farmers realising it.

The UK government's fears appear to be borne out by the new study, led by Dr Nick Savill, of the university's centre for infectious diseases.

Using computer modelling, Dr Savill found that, in practice, it is very hard to protect more than about of 90% of the birds in any given flock, and protection levels are usually much lower. </td></tr></tbody></table>

http://www.theherald.co.uk/news/68064-print.shtml

 

[sharon sanders]

Re: Bird flu vaccination can ?worsen spread?

More info on control of H5N1 in flocks -


http://www.flutrackers.com/forum/showthread.php?p=26029#post26029

 

[Snowy Owl]

Incomplete vaccination could worsen the spread of avian flu

Incomplete vaccination could worsen the spread of avian flu

Incomplete vaccination could worsen the spread of avian flu
Aug 18, 2006, 18:40, Reviewed by: Dr. Priya Saxena
http://www.rxpgnews.com/world/epidemics/avianinfluenza/article_4861.shtml

"The research underlines that vaccination, if used, should be part of a comprehensive control strategy including biosecurity, surveillance and diagnostics, education, movement restrictions and elimination of infected birds."

By University of Edinburgh, Incomplete vaccination of poultry flocks could make the spread of deadly strains of avian flu such as H5N1 worse, scientists at the Universities of Edinburgh and Warwick have found. The research shows that even though the available vaccines are effective on individual birds, the disease is likely to spread unless almost all of a flock has been protected. The study, published in Nature journal, is the first to quantify how incomplete vaccination of flocks can contribute to the undetected spread of the disease.

Vaccination of commercial poultry against highly pathogenic avian flu like H5N1 is proving controversial because it is thought that it can lead to unseen transmission between poultry farms, a phenomenon known as 'silent spread'. This unseen transmission occurs because as protection levels rise in a flock, it becomes ever harder to detect the spread of avian flu quite simply because fewer birds die. The result is increasing amounts of bird flu virus contaminating the birds' surroundings without farmers realising it.

In practice, it is very hard to protect more than about 90 per cent of the birds in any given flock, and protection levels are usually much lower than this. The new study estimates that protection levels of more than 95 per cent would be needed to guard against silent spread.

The study, funded by the Department of Environment, Food and Rural Affairs, suggests that the most effective way of tackling silent spread of the disease would be to place unvaccinated 'sentinel' birds in poultry flocks. By monitoring birds carefully, silent spread could be reduced (though not completely eliminated) because sentinels allow for the rapid detection of bird flu, irrespective of the level of vaccine protection in a flock.

Dr Nick Savill, of the University of Edinburgh's Centre for Infectious Diseases, said: "Vaccination reduces the chance of birds becoming infected and reduces the amount of virus they shed and the time over which they shed it. If vaccination is to be used it needs to be done extremely well or it could make the problem worse, rather than better.

"The research underlines that vaccination, if used, should be part of a comprehensive control strategy including biosecurity, surveillance and diagnostics, education, movement restrictions and elimination of infected birds."

- Nature journal

www.ed.ac.uk

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