DEFRA has made public supporting
data behind the successful licensing
of the first tuberculosis vaccine for
badgers (Badger BCG), which was
licensed by the Veterinary Medicines
Directorate in March this year.
The studies were carried out by the
Veterinary Laboratories Agency (VLA)
and the Food and Environment
Research Agency (FERA).
The laboratory studies with captive
badgers demonstrated that the
vaccination of badgers by injection with
BCG significantly reduces the
progression, severity and excretion of
Mycobacterium bovis infection.
Big reduction
A key finding of the field study,
conducted over four years in a naturally
infected population of more than 800
wild badgers in Gloucestershire, was
that vaccination resulted in a 74%
reduction in the proportion of wild
badgers testing positive to the antibody
blood test for TB in badgers.
But a number of reservations are
listed: (1) the blood test is not an
absolute indicator of protection from
disease, so the field results cannot give
the degree of vaccine efficacy; (2) data
from the laboratory and field studies do
not lend themselves to giving a
definitive figure for BadgerBCG vaccine
efficacy; (3) the data do not provide
information on the effect of badger
vaccination in reducing TB incidence in
cattle.
A paper summarising the results of
the research has been accepted for
publication by the journal Proceedings of
the Royal Society B (Biological Sciences) and
will be published shortly.
Computer modelling
DEFRA has also published the results
of new computer modelling by the
FERA which has examined different
strategies for controlling TB in badgers,
including both culling and vaccination.
The results of the modelling were
consistent with the conclusions of the
Randomised Badger Culling Trial
indicating that there were both positive
and negative effects of culling.
The modelling shows that badger
vaccination could make a positive
contribution to disease control in its
own right and was consistently positive
when used in combination with culling
in a ring vaccination strategy.
The results of the modelling were
that:
- A combined strategy of vaccination
in a ring around a culling area was more
successful than the cull-only strategy,
which in turn was more successful than
the vaccination-only strategy, both in
reducing the number of TB infected
badgers and cattle herd breakdowns.
Ring vaccination partly mitigated the detrimental effects of culling.
However, the combined strategy
requires about twice as much effort
than either single approach done in
isolation. - Culling of badgers should continue for at least four years to realise a clear
benefit. However, low rates of land
access for culling, or low culling
efficiency, or the early cessation of a
culling strategy was likely to lead to an
overall increase in cattle herd breakdowns (whilst this is not the case
for vaccination).
- The results of the research have been
published on the DEFRA website and
are available at ww2.defra.gov.uk/food-
farm/animals/diseases/tb/.
