Betty in Holland has forwarded this message about the recently published
report that claimed to model the impact of vaccination during the UK
epidemic. It has been roundly criticised for only modelling a strategy that
was never likely to work in the first place. Here the authors respond to
FOOT & MOUTH DISEASE - UK (62)
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Tue 21 Aug 2001 23:13:16 +1200
From: Professor Roger Morris <R.S.Morris@massey.ac.nz>
Foot and mouth disease modelling work - response to comments received
[When I posted Paul Sutmoller's critique of the Morris model [RS Morris et
al. Predictive spatial modelling of alternative control strategies for the
foot-and-mouth disease epidemic in Great Britain. Vet Rec 2001; 149(5):
137-44. <http://www.vetrecord.co.uk/abs481.htm>], I simultaneously copied
the critique to Roger Morris and John Wilesmith. Their response is as
follows. - Mod.MHJ]
The comments we have received through ProMED-mail and other sources on our
analysis of control options for the foot and mouth disease (FMD) epidemic
in Britain (ProMED-mail V 2001, #183) have focused largely on the merits of
vaccination, and the way in which we used vaccination in the model. The
correspondents raise some useful issues, but miss the point of what we are
reporting in the paper.
The analyses were conducted over a relatively short period in late March
and repeated with an enhanced farms database in early April. They have been
reported exactly as they were conducted at the time, as a record of
predictions made early in the epidemic, not with any later adjustment for
the wisdom of hindsight. It was then a month into the epidemic, and
considerable controversy was raging about the feasibility and merits of
different control strategies. Our goal was to predict the scale and
duration of the epidemic under various control strategies that were under
consideration and others that were being promoted as superior alternatives
by various commentators.
At the time, it was apparent that the geographical distribution and scale
of the epidemic were both quite uncertain. With the hindsight provided by
epidemiological records of the epidemic, we now know that on March 27 the
number of known infected farms diagnosed as of that date in the epidemic
was 707. However, subsequent evidence shows that on that same date there
were 342 infected premises that had not yet been detected -- the highest
figure this indicator reached. Thus, any control strategies evaluated had
to take account of this uncertainty. The reality, as we now know (and as
"InterSpread" predicted), was that over half of all farms infected in the
epidemic by late August were already infected at the time the simulations
were run, and the expected benefit of control strategies at that date was
influenced within InterSpread by the evolution of the epidemic to that
point. Simulations were run for 200 days, because that was a reasonable
planning horizon at that stage of the epidemic, and realistic control
strategies achieved eradication within that time period.
Given what was known at the time, InterSpread predicted that, with the
control policy being applied, the epidemic would be about 1800 to 1900
farms and would be eradicated between July and October, with a low
probability of extending longer. Its predictions both at the national scale
and in later finer-scale analyses have proved to be remarkably close to
field reality. We intend to report some of these later results in future
Given the extremely wide spread of infected farms in late March and the
expectation that there were more yet to be discovered, classical ring
vaccination was not a feasible option. With the amount of vaccine and
number of vaccinators available for immediate use, a joint stamping
out/vaccination policy was evaluated in the 3 areas with the highest
concentration of infected farms, to damp down the epidemic in those areas
and prevent further outward spread. Because cattle were at the time still
indoors, and there was concern about the risk of transmission to cattle
from sheep when the cattle were put out to pasture, the decision was made
to evaluate cattle vaccination as a cost effective way of reducing further
transmission during the stamping-out process. The model predicted that this
would reduce the scale of the epidemic by under 100 premises. Vaccinating
sheep as well would have reduced this somewhat further. However, it was not
considered feasible at the time to provide sufficient vaccine and
vaccinators to achieve this quickly; and at best it could have had a modest
additional effect, for a very large effort.
There was considerable enthusiasm in some quarters at the time for
abandoning stamping out and simply vaccinating to control the disease. This
would have greatly lengthened the time before eradication could be
achieved; moreover it was considered that vaccination alone was not a
realistic control option. However, it was decided to include vaccination in
order to answer those who saw it as a panacea. The problem then was how to
allocate vaccine on the scale realistically achievable in the short term,
if stamping out was to be abandoned. The decision was made to use it to
shield the main uninfected areas from the known foci, so that if possible
the disease would not spread through the whole country. The vaccination
bands were therefore drawn up to protect what were then free areas, and to
focus the available vaccine on cattle, given that the country was under a
movement standstill and the benefit per dose should be higher from
investing it on cattle. The bands were approximately 20 km wide, so they
were significant barriers. They were certainly equivalent to the diameter
of the mandatory surveillance zones that form the basis for delineating the
formal "infected areas".
Many different "vaccination only" scenarios were possible, but we would
challenge the critics to come up with a strategy that would be
substantially better than the one tested, with the scale of vaccination we
believed at the time was feasible immediately. Our experience elsewhere in
the world would certainly endorse the merits of blanket vaccination and
extension to other species, but that was seen as impractical at the time,
and as greatly extending the expected time to achieve FMD-free status
again, compared with stamping out. It is believed that the modelling work
done was a valuable guide to the relative merits of the options then
available and being discussed, and the InterSpread model has certainly
proved very usefully predictive then and since.
Finally, we stress that we are not opposed to vaccination, but were trying
to identify epidemiologically sound strategies to deal with an
exceptionally diffused epidemic. Vaccination is clearly a valuable element
of many FMD control strategies, but it is not a panacea, and the debate on
this issue in the context of the current British epidemic needs to take
full account of the facts of the situation in late March, when options were
Roger Morris and John Wilesmith for the authors of the Veterinary Record
Roger S Morris MVSc, PhD, FAmerCE, FACVSc, FRSNZ
Gilruth Professor of Animal Health
Director, Massey University EpiCentre
Institute of Veterinary, Animal and Biomedical Sciences
Massey University, Palmerston North, NEW ZEALAND
Ph +64 (0)6 350 5031 Fax +64 (0)6 350 5716
Meet us on the Web: <http://epicentre.massey.ac.nz>
[We are grateful to Roger and his coauthors for their reply. An informed
colleague working in the field in the UK made the following comment to me:
Whilst Dr Sutmoller's comments may well be correct in the different
possible vaccination strategies, it should be pointed out that evidence to
date does not indicate either "smoldering" infection in the national sheep
flock or infection in deer. All tests of deer to date are reported as
negative. It seems most likely that early reports of mortality in deer were
describing malignant catarrhal fever. In Wales it seems most probable that
the infection got onto the Brecon Beacons from neighbouring lowland sheep;
this is certainly the case in the few cases where sheep on common land have
been found with infection in Cumbria. There have been quite a number of
blood tests of fell sheep in Cumbria from the beginning of the outbreak,
and all have been negative, except where the sheep had either been brought
in close to the farm buildings recently [and therefore in proximity to
other stock], or where disease has run up against the common land in
lowland cattle or sheep. The implication in Dr Sutmoller's e-mail that the
disease is running through sheep and spilling over into cattle from there
is not currently the case in the area I am working in; most transmission
has been cattle-to-cattle with significant sheep involvement only when the
disease has reached predominantly sheep areas. Clearly this predominantly
ovine FMD epidemic is teaching us many new facts about an old disease, for
which the collective experience has been very largely with bovine and
porcine FMD. - Mod.MHJ]
Our comment: We remain unconvinced that the vaccination strategy poposed
was anything other than a complete waste of time, and which required no
modelling process to reach the very obvious conclusion that it would be
ineffective. The assumptions of most appropriate use of available vaccine
and manpower seem to us to be so badly flawed that it is difficult to take
the report seriously, despite the background credentials of its authors.
Andrew Stephens' earlier critique of the report still applies as far as we
But do take note of some key facts from the above message, mentioned almost
"we now know that on March 27 the number of known infected farms diagnosed
as of that date in the epidemic was 707. However, subsequent evidence shows
that on that same date there were 342 infected premises that had not yet
This confirms that before the contiguous and 3 km culls had been implemented
(they had only just been announced by March 27th), over one thousand
premises had already become infected, more than half the "final" total
(though it is not finished yet) within the first four weeks of the epidemic.
This is the classic FMD outbreak situation with a rapid rise to an early
peak of case numbers, followed by a lengthy and uneven decline back down to
zero. The draconian culling policies had little impact on this pattern,
which was already clearly established by late March as these authors
confirm. All they did achieve was to pile up the dead bodies for no
benefit. Quote by Bob Mitchell, former President of the RCVS: " The claim
that the extended cull caused the downturn in the epidemic, rather than
coincidentally preceding it, requires strong scrutiny, region-by-region,
allowing for incubation periods. The decline of the epidemic in 2001,
halving from peak in two weeks and halving again in another two looks very
similar to the pattern established in 1967. "
# # #
From the Telegraph:
Farming is ranked fifth at Beckett's ministry
By Sandra Barwick
MARGARET BECKETT's new ministry handling the countryside has produced a set
of draft aims which put protecting the environment first and promoting
sustainable farming fifth.
The priorities of the Department of Environment, Food and Rural Affairs were
attacked by the Country Land and Business Association, which said the
proposed aims were the wrong way round.
Nick Way, director of policy for the association, said: "The first priority
should be thriving economies and communities in rural areas. There can be no
successful sustainable development or environmental conservation without
The department, which has replaced the Ministry for Agriculture, Fisheries
and Food, was criticised at the time of its formation for dropping
Agriculture from its title altogether.
Damian Green, shadow agriculture spokesman, said yesterday: "With every week
that passes, it is clear the Government does not regard farming as important
for the future of rural Britain."
The draft consultative paper, which appeared on the department's website
this week, lists protecting and improving the environment as its first
The second is "to enhance opportunity and tackle social exclusion in the
countryside by leading the development of a dynamic, inclusive and
sustainable economy in rural areas".
The recovery strategy for areas hit by foot and mouth comes under that
heading. Promoting a sustainable, competitive food supply chain for
consumers comes next, followed by improving enjoyment of the countryside for
all and fair access to services for those in rural areas.
Not until objective five is "promoting sustainable, modern and adaptable
farming" tackled along with the eradication of existing foot and mouth
The sixth objective is the promotion of sustainable use of natural
resources, including increasing the recycling of household waste and working
towards sustainable British fishing.
Richard Burge, chief executive of the Countryside Alliance, said: "If these
are listed in order of priority, we should be very worried.
He said: "These should all be equal objectives. This is a crucially
important document. There is nothing about country sports and nothing about
the way of life in the countryside." The alliance is sending the document to
all its members and is soliciting responses.
Ben Gill, president of the National Farmers' Union for England and Wales,
said it would be looking closely at the issues. He said: "While the
headlines are important, it's the content and delivery of those areas that
The closing date for responses to the document, by email, post or on-line at
www.defra.gov.uk is Sept 28.
For the second time this month spinal cord, one of the animal parts seen as
most likely to carry BSE, has been found in beef imported from Holland.
The discovery was made on Tuesday in four out of 236 quarters of beef being
unloaded at the company ADM in Eastbourne, East Sussex, the Food Standards
Agency said yesterday.
From the Yorkshire Post:
Council chief urges security cordon to protect upper dale from disease
A NEW high-security cordon is being demanded to defend Upper Swaledale from
foot-and-mouth disease raging just over the Pennine watershed in Cumbria.
Though Swaledale has remained disease-free, there are growing fears it could
be at risk from the Kirkby Stephen and Appleby hotspots in Cumbria which are
as close as six miles away.
The Department for the Environment, Food and Rural Affairs (DEFRA) has
imposed a 100-square mile high biosecurity zone on the Penrith area
including Brough, Kirkby Stephen and Appleby.
But North Yorkshire County Council leader John Weighell fears that outbreaks
around Kirkby Stephen and Appleby threaten the disease-free status of the
moorland sheep in Upper Swaledale and could trigger another hotspot.
DEFRA's efforts in North Yorkshire are concentrated on the 900-square-mile
high biosecurity box in the Vale of York, designed to stop the disease
spreading into thousands of pigs in the East Riding and Lincolnshire.
But Coun Weighell is urging North Yorkshire Trading Standards staff to begin
planning for the introduction of special precautions to protect the moorland
flocks grazing thousands of acres in Upper Swaledale.
Coun Weighell said: "There are very few farms because of the sparsity of the
population and only a few roads involved, so it ought not to be too
difficult to enforce."
He added: "I accept the Vale of York has to be the priority, but if there is
any rundown in the intensity of the operation in the Thirsk box, then there
may be resources available for Swaledale. It is being thought through."
A DEFRA spokeswoman said: "We are considering moving the boundary of the
Penrith box eastwards in the light of the current movement of foot-and-mouth
but no final decision has been taken."
Since DEFRA imposed the high security zone in Cumbria 16 days ago there have
been 31 foot-and- mouth cases, leading to the slaughter of another 3,723
cattle and 7,834 sheep.
From the BBC website:
New farm disease case raises fears
A new case of foot-and-mouth has been confirmed by government scientists in
Northumberland, sparking fresh fears about the disease.
It is the first case in the region for nearly 12 weeks.
Three cows and their calves which were showing signs of infection were
slaughtered on Thursday night at a farm near Hexham, said a spokesman for
the Department of Environment, Food and Rural Affairs (Defra).
The news comes just days after the first live UK cattle auction since the
outbreak of the disease was allowed to take place in the Orkney Islands.
The Defra spokesman said the remaining animals on the Northumberland farm,
both cattle and sheep, were being slaughtered on Friday.
A spokesman for the National Farmers' Union (NFU) said he hoped the new
outbreak would turn out to be an isolated case.
"Isolated cases are not unexpected and we have had similar isolated
outbreaks of this kind recently.
"Checks will need to be carried out to determine its origin."
But he added: "This is a stark reminder to all livestock producers and
people visiting farms to ensure that they are continuing to do everything
possible to guard animals against risk."
Defra's divisional veterinary manager for the region, Arthur Griffiths,
said: "It is a serious setback and will delay the eventual freeing of
Northumberland from all restrictions by several weeks."
He said every farm with 3km of the infected area would be closely monitored,
though it was hoped the disease had been spotted quickly.
"There were no clinical signs before last Tuesday or early on Wednesday so
it does not look as though the virus got into the cattle much more than
about 12 days ago," said Mr Griffiths.
He added: "An intensive investigation is going on to establish how this
outbreak has occurred well over two months after the last case in the north
John Bradbury, Defra's regional operations director based at Newcastle
Disease Emergency Control Centre, said disease experts "would not be
surprised" by the fresh outbreak.
But he added: "This is a severe blow to our hopes of achieving disease-free
status for the north east and a big disappointment for farmers in the
region, as well as vets and others who have been working so hard to
eradicate the disease."
All for tonight
from Alan & Rosie