Sunday, October 29, 2017

Infectivity of vaccinated badgers

Last week, UCD Centre for Veterinary Epidemiology and Risk Analysis, UCD School of Veterinary Medicine, University College Dublin, and the Quantitative Veterinary Epidemiology group, Wageningen Institute of Animal Sciences, Wageningen University & Research, Netherlands published a paper -[link] on the vaccination of badgers.

 Over four years, groups of badgers were jabbed with either BCG or a placebo and then tested for results. The paper describes:
In this manuscript, we present the results of a badger field trial conducted in Ireland and discuss how the novel trial design and analytical methods allowed the effects of vaccination on protection against infection and, more importantly, on transmission to be estimated.
Cutting through all the guff, we pick out the following paragraphs:
Over the study period, 55 new infections occurred in non-vaccinated (out of 239 = 23.0%) and 40 in vaccinated (out of 201 = 19.9%) badgers.
This is 'protection against infection'  part. So after vaccinating, a difference of  just 3 per cent? But then the modelers got to work, and "Statistical analysis showed that susceptibility to natural exposure with M. bovis was reduced in vaccinated compared to placebo treated badgers: vaccine efficacy for susceptibility, VES, was 59% (95% CI = 6.5%-82%)." But crucially:
However, a complete lack of effect from BCG vaccination on the infectivity of vaccinated badgers was observed, i.e. vaccine efficacy for infectiousness (VEI) was 0%.
Infectivity of badgers is the amount of detritus left behind for any other mammal to fall over. That's the 'transmission' bit. Especially important for our sentinel, tested cattle, and described in the paper as " extremely important in the case of vaccination in badgers, as the ultimate goal is to help in the control or eradication of M. bovis infection in cattle."

 Not just in Ireland either. Our lot have been playing with BCG (at 10x the rate for humans) for several years. We discussed their results here - [link] and veterinary professionals gave their view here - [link]
And we also remember poor old badger D313 - [link] who had his dose of BCG and developed zoonotic Tuberculosis in pretty much every organ, during the Lesellier trial. -[link]

So the paper's 'stand out' paragraph for us is this blinder:
A reduction in the total infectivity of vaccinated and subsequently infected badgers in the field had been anticipated based on the reduction in disease progression observed in vaccinated compared to non vaccinated badgers in experimental studies (Chambers et al., 2011).

However, no reduction of infectivity was found in our study. The lack of effect of BCG vaccination on infectivity in the general badger population is thus at odds with the hypothesis that vaccination, by reducing disease progression, reduces the infectivity of vaccinated and subsequently infected badgers.

From this study, we cannot determine whether a similar reduction in disease progression to that observed in experimental studies was found in the field as no post-mortem data were available. Nevertheless, if that reduction in disease progression does exist, we did not find a concurrent reduction in infectivity. The lack of effect of vaccination on infectivity has implications in terms of the effectiveness of BCG badger vaccination in Ireland (or how much reduction of transmission is achieved by vaccination).
Post mortem data was available to Lesellier, and those vaccinated badgers all had lesions and all were shedding. (Link above)

The Farmers Union of Wales understands only too well, how ineffective faffing about with vaccinating badgers is. In an an article - [link] published by the Institute for Welsh Affairs earlier this year, Dr. Nick Fenwick describes the result of four years of vaccinating:
So it comes as little surprise that the latest official report on the badger vaccination programme in north Pembrokeshire, which cost £3.7 million, concludes that “Consistent trends in indicators of bTB incidence have not yet been seen…”
Perhaps someone should tell The Badger Trust, Rosie Woodroffe,  Brian May, and even the Secretary of State - link] And also ask, with these results echoing those of Lessellier in 2011, why on earth anyone is still promoting and funding this?  

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