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INFORMATION FROM INTERVET ABOUT THE EFFICACY
OF VACCINES
Avian Influenza - Research papers
In order to help you to establish a more balanced view about the role
vaccination can play in controlling AI, we would like to provide you with
further information to address the misinformation that has recently been
reported in the media - messages such as 'vaccine only masking the disease'
or 'driving it underground', 'it makes surveillance difficult', 'costly'
etc. Vaccination on its own is insufficient, however, when it is used
combined with depopulation, strict biosecurity and surveillance, it becomes
a cornerstone of a very successful strategy, enabling producers and authorities
to bring this devastating disease under control.
Scientific factual evidence (Halvorson, Avian pathology (2002) 31, 5-12)
confirms that inactivated vaccines have:
" reduced the flocks susceptibility to AI infection,
" reduced the quantity of virus shed post challenge,
" reduced transmission, and
" markedly reduced disease losses.
We have prepared a collection of summaries and quotations from reputable
authors containing other factual evidence.
Field challenge studies
T. Ellis, C. Leung, M. Chow, L. Bissett, W. Wong,
Yi Guan & J. S. Malik Peiris. Vaccination of chickens against H5N1
avian influenza in the face of an outbreak interrupts virus transmission.
Avian Pathology, 33(4), August 2004, pp 405-412]
In Hong Kong the Intervet H5N2 vaccine was used in the face of an outbreak,
including on farms where the virus was circulating and where the birds
were not culled. As from 18 days after vaccination the vaccine completely
stopped virus circulation on the farm. In addition to quarantine, depopulation
of the affected sheds and increased biosecurity, vaccination of the affected
sheds and surrounding farms resulted in complete control of the disease.
"One of the concerns in the use of vaccine to control HPAI in poultry
farms is the possibility that while vaccine may protect from disease,
asymptomatic virus circulation may continue, resulting in spread of infection
to other farms. The monitoring and surveillance conducted in these three
chicken farms showed that use of this killed H5N2
vaccine in the face of HPAI virus challenge was able to protect chickens
from disease and interrupt virus transmission… This investigation
showed that the use of killed H5N2 vaccine on three farms was able to
protect chickens against disease and also to interrupt asymptomatic shedding."
Laboratory challenge studies
David Swayne (Southeast Poultry Research Laboratory, USDA/ARS, Athens,
Georgia. US) is publishing a challenge experiment with SPF chickens vaccinated
with Intervet's H5N2 vaccines from Mexico and Spain. The birds were challenged
with a large dose of H5N1 Asian field isolate. The vaccines protected
completely against mortality and morbidity. All non-vaccinated birds excreted
large amounts of virus. The majority of vaccinated birds did not excrete
any virus, the minority excreted 10,000 to 100,000 times less virus than
controls. The results are being published, and a summary is available
at www.avian-influenza.com. [This follows Swayne's earlier published work:
Efficacy of vaccines in chickens against highly pathogenic Hong Kong H5N1
Avian Influenza. David Swayne, J. Beck, M. Perdue & C. Beard. Avian
Disease, 45 (2), April 2001, pp 355-365].
In an outbreak of Avian Influenza, reduction of virus circulation is a
very important factor in preventing spread of Avian Influenza to other
birds and to people. Reduction of virus excretion significantly reduces
the chance that an infected farm will infect another farm. The above experiment
shows that vaccination with the tested vaccines can make an important
contribution to the control of Avian Influenza outbreaks.
Transmission experiments
L.A.van der Groot et al.: Quantification of the effect of vaccination
on transmission of avian influenza (H7N7) in chickens. PNAS; December
13,2005;Vol 102; no 50,18141-18146
In the Central Institute for Animal Disease Control, Lelystadt, The Netherlands
they studied the effect of vaccination with H7N1 or H7N3 vaccines on the
transmission characteristics of HPAI H7N7 in chickens. The results of
the experiments demonstrate that vaccination not only protects chickens
against disease symptoms and mortality but is also an effective strategy
to reduce transmission. Vaccination with Nobilis Influenza
H7N1 resulted in adequate protection against a severe challenge by as
early as one week post vaccination. When birds were challenged 2 weeks
after vaccination, transmission of the virus to contact birds was completely
blocked. The conclusion of the experiments was that vaccination of poultry
can be an effective tool to prevent the spread of highly pathogenic AI
viruses.
Ducks: A similar transmission study at Lelystadt demonstrated that vaccination
of ducks with Intervet's H7N1 vaccine completely blocked the challenge
virus (H7N7) virus transmission from infected vaccinated ducks to contact
vaccinated ducks.
If you would like to receive copies of any of the above articles please
contact Cally Grubb on 01908 685 249. We would also like to know your
views about vaccination against Avian Influenza and you can share your
thoughts with us via our website www.intervet.co.uk or by email cally.grubb@intervet.com.
Dr Tibor Cserep DVM MRCVS
Technical Manager Poultry Products
Intervet UK Ltd
Walton Manor
Walton
Milton Keynes
MK7 7AJ
Telephone : 07711 450719
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