VACCINES are supposed to prevent disease. But for the first time
we have evidence that a lethal virus has developed from vaccines
that were meant to protect against it. In 2007, something
different happened. Chicken farmers in Australia were using two
live vaccines, both made from Australian viral strains, against
a poultry disease called infectious laryngotracheitis (ILT).
Then they began using a third live vaccine containing a European
strain. The following year, they saw outbreaks of new forms of
ILT. Glenn Browning at the University of Melbourne in Australia
and colleagues sequenced the viruses and found that they arose
when the European strain acquired genes from the Australian
strains. The real surprise was that, unlike the vaccine viruses,
the hybrids were as deadly as wild ILT (Science, DOI:
10.1126/science.1217134). Other unexplained disease outbreaks
may have a similar cause, Browning says. If you would like to
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