Foot-and-Mouth would have
Vaccine model suggests a shot in the rump is
worth two in the head.
23 December 2002
Six million farm
animals died in Britain's 2001 foot-and-mouth outbreak.
vaccination would not have halted Britain's devastating 2001
foot-and-mouth disease (FMD), a new analysis suggests1.
prophylactic vaccination or targeting high-risk farms first are the
to avert or minimize future outbreaks of FMD, say the report's
Matthew Keeling of the University of Warwick, UK, and colleagues.
tactics, they reckon, could work for other animal and even human
such as influenza and smallpox.
The heat from pyres of burning carcasses
has died down, but argument about
the management of Britain's worst-ever FMD
outbreak has not. More than 6
million animals, mainly cows, sheep and pigs,
were slaughtered before the
Vaccination wasn't used
because of pressure from farmers. Under current
European law, vaccinated
animals cannot be bought or sold.
New tests for distinguishing vaccinated
animals from infected ones, and
strategies such as those proposed in the new
study, show that it's "time for
the rule book to catch up with the science",
immunologist Ian McConnell of the University of
Based on data from the 2001 outbreak,
Keeling and his colleagues designed a
model that predicted the infectious
state of every farm in Britain each day.
They then replayed each day of the
seven-month outbreak with four different
Nation-wide vaccination of all animals before an outbreak
greatest protection. Localized culling on and around infected
still required, as there are always gaps in vaccine
Mass vaccination in response to an outbreak was the next best
FMD vaccine takes seven days to confer immunity, so extensive
again required. In the model, this strategy knocked four months
Ring-fence vaccination - where farms surrounding
infected hotspots are
treated to contain the disease - failed because of
vaccination-to-immunity lag and the rapid movement of animals before,
for a time after, the outbreak was detected. Without a complete movement
on animals and people, says Keeling, "sparks of infection jump out of
rings" and propagate the epidemic.
The researchers also used their
model to identify a 'predictive' vaccination
strategy to be used in response
to an epidemic. This tactic targets the
farms at greatest risk. In the model
it shortened the outbreak almost as
much as mass vaccination.
that the necessary information about farms and animal movements is
before an outbreak, the predictive approach is preferable, says
Mass vaccination requires large amounts of vaccine and systems
it. In most parts of Europe, which suffer only occasional
doesn't make economic sense. Predictive vaccination is "a
The poor performance of ring-fence vaccination in Keeling's
that it might fail for other diseases too. Infectivity and
different for different diseases, but "all have this
says Keeling. Indeed, recent research showed that
probably wouldn't contain
Keeling, M. J., Woolhouse, M. E. J., May, R.
M., Davies, G. & Grenfell, B.
T. Modelling vaccination strategies against
foot-and-mouth disease. Nature,
Published online, doi:10.1038/nature01343
Kaplan, E. H., Craft, D. L. & Wein, L. M. Emergency
response to a smallpox
attack: The case for mass vaccination. Proceedings of
the National Academy
of Sciences, 99, 10935 - 10940, (2002).