Another look at the Veterinary Record (Aug 4th) Article of vaccination modelling

(Updated comments since Andrew's first quick look at the article)

This study (funded by DEFRA) only modelled one strategy for vaccination - a strategy that I've never ever seen mentioned elsewhere as a possibility - no doubt because it's patently daft. It divided UK into 6 large zones by bands of vaccination ('firewalls') and the zones are often HUGE.

For example, the whole of Northern England was one zone. Only cattle - not sheep or pigs - would be vaccinated in the modelled strategy (so the 'firewall' would of course be permeable!) and no slaughter - even of infected animals - would take place anywhere - just this permeable band vaccination of cattle alone.

One doesn't need to be a rocket scientist to realise that such a vaccination strategy would be almost entirely useless in preventing the spread of the virus.

The 'justification' for only modelling this absurd use of vaccination is the claim that this is/was the only form of vaccination campaign that could have been mounted at the time under consideration - around the end of March - due to resource (vaccine and manpower) constraints. In my opinion this is complete rubbish.

I hate to say it but it does appear that this paper (The Veterinary Record) has two goals -
a) to retrospectively justify the (unjustifiable) contiguous cull policy and
b) to " trash" vaccination.

I had thought that the major authors had more integrity than that - but perhaps not. Of course there's no way DEFRA - who funded the study - would have allowed publication of any results that did not support their policies. I cannot imagine that the absurd vaccination strategy for which results are presented was the only vaccination strategy modelled - but perhaps DEFRA blocked publication of any other results?

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The earlier comments

It's a very extensive and complex article - but the only ( I think) vaccination strategy modelled was one of buffer zones/bands that subdivided GB into 6 zones. ie a sort of multiple firewall type strategy. The authors claim this represented the only vaccination strategy that could have been mounted at the time (end March) given available resources.

I'm not surprised that the InterSpread model predicted a very large epidemic if this - buffer zone/band vaccination - was the *sole* control measure undertaken - after all the epidemic(s) could run wild within each of the zones where infection had already got a grip until it reached the vaccinated firewall buffer. For example, the whole of Northern England was one zone.

This modelling study does NOT say that vaccination per se would not and could not have been effective - instead it says that this particular buffer zone/band style of vaccination - which it is claimed is all that could have been done at the time for resource reasons would not have been effective.

They did not for example model blanket vaccination using high load vaccine within and around emerging hotspots combined with slaughter of definitive IPs, or any of many other possible vaccination strategies that could have been considered had resources not been the constraint they claim they were. Were these assumed constraints real?

The InterSpread model - although FAR superior to the Ferguson, Anderson, Donnelly model - also used early field data - up to April 10 in this study - which is known to have been 'dodgy'.

It's important to consider exactly what this paper does and does not examine in its correct, now historical, context.

No doubt -sadly - there will be many who cite this paper to claim that it says that vaccination doesn't work in controlling FMD.


Footnote: About the InterSpread model - part of the EpiMan information system for emergency disease control - which has a long history and a good reputation.

The Morris/EpiCentre team at Massey Uni, NZ has an excellent and deserved reputation for VETERINARY epidemiological modelling and use of computers in ANIMAL disease control. We should not throw out the baby with the bathwater.

The InterSpread model - part of the EpiMan information system for emergency disease control - has a long history and is has a good reputation.

InterSpread models species separately, model actual locations of farms, and accommodates the effects of chance when forecasting patterns of disease. It is a FAR more sophisticated and well validated system than that hacked together by Anderson et al.

Models of this sort are actually very helpful in exploring likely patterns of disease and disease spread in POPULATIONS of animals - as opposed to lab experiments that typically only explore development of disease in individual or very small numbers of animals in a lab setting. They often reveal insights that cannot be gained any other way - the human brain just doesn't handle 'calculating/forecasting' how a disease behaves at the population level very well - and often what appears to be 'common sense' turns out not to be when explored with computer simulation models. Epidemiology is a branch of medicine that 'looks at' the 'natural history' of disease at the population level - rather than at the individual level.

The study only explores one (in my opinion daft) vaccination strategy. The results risk being interpreted as saying 'vaccination doesn't work' - but that is NOT what the paper says - it says that one (absurd) strategy for vaccination probably would not have worked. I fact the vaccination strategy modelled is so absurd that even the 'man in the street' could have figured out that it would be ineffective.

It's also true to say that the field data - from the early weeks of the epidemic - used to parameterise this model - and others - is known to be of somewhat dubious quality, but it's not clear (to me anyway) how much impact this would have on the results of the modelling studies.

Regards Andrew