Memorandum by Professors Martin J Newby
and Professor Philip J Thomas, Centre for Risk Management, City
University
This evidence is submitted on an individual
basis.
RATIONAL ASSESSMENT OF RISK PREDICTIONS:
THE LESSONS OF BSE AND VCJD
SUMMARY
1. We believe that two main issues may limit
the effectiveness of Government's response to the threat of a
new infection:
(i) the lack of critical judgment on the
part of senior civil servants and Government ministers when faced
with scientific issues;
(ii) the consequent tendency to rely too
heavily on a scientific advisory committee, which may in practice
exceed its role by promoting one particular viewpoint to the exclusion
of others both to ministers and in the scientific literature.
2. In addition, recent experience suggests
that Government may be uncomfortable with the concept of finite
but acceptable risk, which is integral to decision making under
uncertainty; Government appears to have baulked at the challenge
of communicating this concept to the public.
3. We believe that the events surrounding
the epidemic of Bovine Spongiform Encephalopathy (BSE) in cattle
and the outbreak of variant Creutzfeldt-Jakob Disease (vCJD) in
humans may be seen as a case-study, illustrating many of the potential
problems.
BSE AND VCJD
AS A
CASE-STUDY
4. The Secretary of State for Health announced
a possible connection between BSE and a new disease, subsequently
known as vCJD on 20 March 1996, based on the 10 cases of the disease
then known. The Secretary of State gave no indication of the likely
size of the outbreak at the time, beyond saying that the chance
of infection was "remote." However, it was possible
even at that early stage to estimate the range of likely sizes
of the human outbreak: it appeared that the number of human victims
would be restricted to hundreds1, 2, 3 and such an assessment
was communicated to the Spongiform Encephalopathy Advisory Committee
(SEAC) in April 1996. The then Chairman, Prof. Pattison (now Sir
John) declared himself against the idea of making estimates, before
suggesting that the numbers might go as high as 500,0004. This
set the tone for the Advisory Committee's subsequent pronouncements:
the phrase "it is too soon to know" was used repeatedly
by SEAC members, while at the same time the spectre was raised
of a 100,000 or many hundreds of thousands of human victims5,
6, 7, 8, 9, 101. Nor was reference made to the low number of human
victims that was, as far as we can tell, generally agreed to be
most likely11, 12, 13. This attitude seems in part to be based
on the view that a full scientific understanding of the disease
was required before any decisions could be made. An estimate of
the size of the outbreak was the key requirement for planning
and decision making, yet the Committee has never adopted a clear
position on the question.
5. We repeated our calculations at intervals,
and found that our predictions for the characteristics of the
human outbreak hardly changed over the years14, 15, 16, 17, assuming
that BSE was the root cause. The period between human infection
and death was estimated as below 10 years, most probably just
above seven years. The most likely number of human victims has
always been calculated to be about 100, and the current estimate
is 130, exactly the same as the figure advanced in 1996. The upper
bound for the number of human victims has always come out as a
few hundred. These figures are fully consistent with the incoming
low figures for vCJD deaths. Confirmed deaths from vCJD stand
at 93 as of 4 October 2002, an increase of just 5 over the past
year18. Including cases classed as "probable", both
living and dead, brings the total to 127, up from 107.
6. However, guided by SEAC's advice that
hundreds of thousands of fatalities were a real possibility, Government
instituted draconian measures after March 1996. While the earlier
countermeasures had cost tens of millions of pounds a year, the
very extensive countermeasures introduced after March 1996 have
cost around £1 billion pounds per year19. These measures
seem to have been introduced without an analysis of either costs
or benefits.
7. We have been able for some time to estimate
the number of lives that might have been saved by this dramatically
increased annual expenditure16, 17. Reviewing all the countermeasures
introduced from the earliest days, we may draw up Table 1.
TABLE 1: RANKING THE COUNTERMEASURES IN TERMS
OF LIVES SAVED
| Measure | Date introduced
| Number of lives saved |
| Ruminant Feed Recycle (RFR) ban | July 1988
| Thousands |
| 50 per cent and 100 per cent Compensation Orders
| August 1988 and
February 1990 | Hundreds
|
| Specified Bovine Offal (SBO) ban | end 1989
| Hundreds |
| Measures after March 1996, including the Over 30 Months Scheme (OTMS)
| April 1996 onwards | Up to about 10
|
8. By far and away the most important countermeasure
was the Ruminant Feed Recycle (RFR) ban, introduced in mid-1988.
This cut off the fundamental source of infection, leading to the
eventual termination first of the BSE epidemic and then of the
vCJD outbreak, although the long incubation periods associated
with both BSE (five years) and vCJD (seven years) have meant that
the process of ending the interlinked outbreaks has been protracted.
Without this measure the number of human infections might have
reached hundreds per year before the first cases of vCJD were
diagnosed, and it is likely that thousands of human infections
would have occurred before the public changed its eating habits
sufficiently to avoid further infection.
9. The next most important countermeasures were the Compensation
Orders and the SBO ban. Each of these measures had been implemented
by early 1990, and each is estimated to have saved hundreds of
lives. Our analysis indicated that the SBO ban had been applied
with an efficiency of only about 66 per cent in the early to mid
1990s, a figure confirmed independently by direct calculation
from the recorded weights of meat and offal20, 21. There is evidence
that the necessary tightening up in the application of the SBO
ban did not happen until 199622. More rigorous enforcement of
regulation in the early to mid 1990s might have reduced the eventual
human death toll by about 100.
10. However, the very extensive countermeasures introduced
after March 1996, including the mass slaughter associated with
the Over 30 Months Scheme (OTMS), were introduced only after the
main danger to human health was almost past. Further measures
could have only a marginal effect since only about 10 lives could
have been at risk, a fact that imposes a low upper limit on their
possible effectiveness.
COMMENTS ON
GOVERNMENT'S
RESPONSE TO
BSE AND VCJD
SINCE 1986
11. As was clarified in the BSE Inquiry23, there were
delays in identifying BSE as a new disease and in introducing
adequate countermeasures against it. Nevertheless, the most important
BSE countermeasure, the RFR ban, came into force in July 1988,
within 19 months of the first formal identification of the disease,
and all the most important measures were in place by early 1990,
although the SBO ban was not enforced properly until 1996.
12. While the early countermeasures were the most effective
in containing the outbreak of vCJD, they did not eliminate the
chance of contracting vCJD completely. Nevertheless it was suggested
initially that these protective measures removed any threat to
humans from BSE and so guaranteed absolute safety. The realisation
in early 1996 that there were likely to be human victims24 caused
an abrupt switch in policy. Government felt unable to sustain
the line that these same measures, subject to strengthening and
limited extension, could form a continuing basis for combating
the disease. Hence Government began introducing immediately a
series of additional countermeasures that were two orders of magnitude
more expensive than those enacted previously. Most importantly,
as has been noted above, the new measures were destined to have
a marginal effect simply because the success of the earlier, much
cheaper measures, which had reduced the number of people at risk
to a low level.
13. An understanding of the limited scale of the problem
would surely have caused the Government to question the wisdom
of authorising the very large expenditure incurred post March
1996 and to explore alternative ways of achieving similar, or
the same, reduction in risk more cheaply. For example, the laxity
already highlighted in the early enforcement of the SBO ban suggests
that major benefit might have been drawn simply by policing existing
countermeasures very much more rigorously.
14. Advice on the probable scale of the vCJD outbreak
was made available to Government at the time1, 2. Unfortunately
the Government chose to be guided by the erroneous view that there
might be a vCJD epidemic with hundreds of thousands of victims.
The Government's continued inability to give proper consideration
to the spectrum of scientific opinion has proved to be very expensive
and must be a major cause for concern. It is clear that those
tasked with devising policy—ministers and senior civil servants—need
to adopt a more critical attitude to the scientific advice they
are offered, even when that advice comes from one of their own
advisory bodies. They need also to be familiar with the concept
of finite but acceptable risk, and realise that absolute safety
is rarely an achievable goal in a hazardous world.
THE ESTABLISHMENT
OF AN
INFLEXIBLE SCIENTIFIC
ORTHODOXY ON
BSE AND VCJD
15. It became evident from 1996 onwards that an inflexible
scientific orthodoxy was becoming established based around the
views of SEAC members27. For example, our difficulties in getting
our first paper published following an initial welcome from Nature
have been documented15. The paper14 was eventually published in
the British Food Journal, but not before the editor of
that journal had felt the need to consult no less than six academic
referees. This unprecedentedly large number was occasioned by
the need to find additional referees independent of SEAC so as
to obtain a properly impartial opinion. Acceptance of the paper
in a refereed journal enabled us to submit evidence to the BSE
Inquiry. Publication of our work stimulated many letters from
within the scientific and medical community expressing relief
at the opening of the debate on the scale of the vCJD problem.
Several other authors offered evidence of the moderate size of
the outbreak28, 29. All these contributions were dismissed by
the Chairman of SEAC. In a similar vein, it is noteworthy since
the more recent publication of Venters' paper30 in the British
Medical Journal how many statements have appeared in that
journal's on-line correspondence column welcoming the first open
discussion on whether a link from BSE to vCJD has truly been established31.
16. It is now apparent that several sets of scientists
previously suggesting very large figures for the potential size
of the vCJD outbreak have at last reduced their top estimates
by several orders of magnitude, thus converging on the low figures
advocated consistently by the present authors. For example, it
was only when the incubation period was assumed to be comparable
with the average lifespan of a UK citizen that one team was able
to reproduce its previous upper bound of more than 100,000 deaths8.
More relevantly, it is striking how that team's estimate of less
than 2900 human victims for an incubation period of 30 years was
a hundred times lower than the figure they advanced just one year
earlier7. Meanwhile groups that included the current Chairman
of SEAC on the one hand, and the past Deputy Chairman on the other,
have now come around to using a similar estimation approach24,
25 to that we have always advocated. Given that they are using
essentially the same methodology, it would be expected that they
would calculate similarly low upper bounds and, indeed, this turns
out to be the case. The Chairman has now stated publicly32 that
the outbreak could be expected to be at most a few hundred victims.
17. Valleron, Boelle, Will and Cesbron replied to our
comments on their paper to the Editor of Science with the
statement that "To be right too early is to be wrong".
We have to disagree with this comment. We find it difficult to
disregard the very large amount of money spent since March 1996
to small effect, the disruption to the beef industry and to international
trade, and the unnecessary fear and suspicion raised amongst the
public.
METHODOLOGICAL ISSUES
18. The modelling within SEAC has not been directed to
supporting decision making, but rather to the exploration and
confirmation of scientific theories. Anderson's group in particular
has used simulation studies which have the weakness described
by the former Government Chief Scientist as "speculative
exploration of . . . epidemiological models whose parameters are
no more than illustrative guesses"33.
19. There has also been a failure to apply logical arguments
about the consistency of empirical data and model predictions.
In 1999 an average incubation period of 30 years was given serious
consideration when the mean age of onset was 26. Furthermore,
since exposure to BSE could have occurred only in the 18 years
since 1984, such a long average incubation period opens the possibility
of another causal mechanism for vCJD. However, wider arguments
about the consistency of data and causal mechanism34 have been
largely dismissed by those close to SEAC34.
CONCLUSIONS
20. Our impression is that ministers and senior civil
servants have been reluctant to apply their own critical judgment
to the problem of BSE and vCJD in the period since March 1996.
They have appeared instead to be content to rely more or less
exclusively on the judgment of a Committee, SEAC, that should
properly have been a source of advice only.
21. It is not unnatural that the research scientists
making up SEAC should be enthusiasts for their own view, but we
have encountered occasions where this enthusiasm has displayed
itself as intolerance of differing views. Scientific debate has
suffered in consequence, and the potential for diverse scientific
advice for Government has been reduced. We feel that benefit would
be gained by reviewing both the make-up and the operational terms
of reference for such scientific advisory committees.
22. A feature of the later stages of the BSE/vCJD crisis
has been the willingness to spend very large sums of money to
avert a small number of fatalities, perhaps under the belief that
this is what the public wants. The problem is that there is competition
for Government money, and that money spent on BSE/vCJD is not
available for other uses, whether it is building new hospitals
or improving the equipment of HM Forces. Nor will it be so easily
available for combating an outbreak of infection that may be much
more serious.
REFERENCES
1. Thomas P J (1996) "BSE/CJD: the need for statistics",
letter to Lord Wade, 2 April. Copy supplied along with WS313 to
the BSE Inquiry in December 1998, held there in "Bundles".
2. Lord Wade of Chorlton (1996), Parliamentary Debates
(Hansard), House of Lords Official Report, HMSO, Vol. 571
No. 76, 17 April, pp. 695-6.
3. Hallberg, Oerjan (1996), "Estimating human BSE
numbers", oerjan.hallberg@swipnet.se; www.hir.nu
4. "It's been six months—should we stop worrying",
interview with Prof. John Pattison, by Victoria Macdonald, Sunday
Telegraph, 22 September 1996.
5. Cousens, S N, Vynnycky E, Zeidler M, Will R G, and
Smith P G, (1997) "Predicting the CJD epidemic in humans",
Nature, Vo,. 385 pp 197-198, 16 January 1997.
6. Ghani A C, Ferguson N M, Donnelly C A, Hagenaars T
J and Anderson R M, (1998) "Epidemiological determinants
of the pattern and magnitude of the vCJD epidemic in Great Britain",
Proc. R. Soc. Lond. B265, pp 2443-2452.
7. Ferguson N M, Donnelly C A, Ghani A C, and Anderson
R M, (1999), "Predicting the size of the epidemic of the
new variant of Creutzfeldt-Jakob disease", British Food Journal,
Vol. 101, No. 2, 86-98.
8. Ghani A C, Ferguson N M, Donnelly C A, and Anderson
R M, (2000) "Predicted vCJD mortality in Great Britain",
Nature, Vol. 406, 10 August 2000 pp. 583-584
9. Interview with Prof. Peter Smith, Chairman of SEAC,
and Prof. Roy Anderson, member of SEAC (2001), The Daily Telegraph,
25 May.
10. Anderson R (2001) "The potential human threat",
The Journal of the Foundation for Science and Technology,
June, pp 13-16.
11. Smith P G, (1999) "Predictions about the future
course of the variant CJD epidemic", BSE Inquiry,
Witness Statement 583.
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WS583 from Professor P G Smith entitled `Predictions about the
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Witness Statement 313B.
13. Thomas, Philip and Newby, Martin, (1999-b) "Reply
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Creutzfeldt-Jakob disease'", British Food Journal, Vol. 101,
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the size of the outbreak of new-variant CJD", British Food
Journal, Vol. 101, No. 1, 44-58.
15. Newby M J and Thomas P J, (1998) "Estimating
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BSE Inquiry, Witness Statement 313.
16. Newby M J and Thomas P J, (1999) "Ranking the
preventative measures for new-variant CJD using data on human
deaths to the end of 1998", BSE Inquiry, Witness Statement
313A.
17. Thomas P J, Newby M J, and Zwissler R (2002) "New
predictions for vCJD numbers", paper submitted to British
Food Journal, September.
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Disease Statistics, www.doh.gov.uk/cjd/stats
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8 July 1998.
20. Fleetwood, Andrew (1998-a), BSE Inquiry, Witness
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21. Fleetwood, Andrew (1998-b) Testimony to the BSE
Inquiry, Day 55, pp 89-93.
22. Ministry of Agriculture, Fisheries and Food (1996)
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29. Southwood, Sir Richard (2000), "Supplementary
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31. On-line correspondence (2001, 2002), British Medical
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32. Smith P (2002) Interview on Farming Today,
BBC Radio 4, 11 October.
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October 2002
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