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1 .This is Scientific American 60-Second Science. I'm Christopher Intagliata. Got a minute?
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2 .In the 1960s a cancer-causing herpes virus was ravaging the poultry industry.
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3 .The virus caused what's called Marek's disease—and killed 1 to 2 percent of the birds.
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4 ."Given that there are billions of birds in the industry, that's a lot of birds."
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5 .Andrew Read, an evolutionary biologist at Penn State University.
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6 .He says the virus was easy to catch.
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7 ."So the dander of chickens if full of the virus. If you shake a chicken, the virus drops out."
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8 .Then, in 1970 a new vaccine put an end to most of the deaths.
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9 .But the poultry vaccine, unlike most, was a so-called "leaky" or "imperfect" vaccine.
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10 ."The vaccine is lifesaving, but it allows the infection to persist and transmit from the host."
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11 .Meaning you could still shake a vaccinated chicken¡ªand make it rain viruses.
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12 .Now, Read and his colleagues have shown that these leaky vaccines may actually give some viral strains an evolutionary leg up.
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13 .Because the most virulent strains usually wipe out unvaccinated birds in just 10 days, not enough time for the birds to infect many others.
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14 .The viruses are essentially so "hot" they burn themselves out.
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15 .But vaccinated birds survive infection with the hot virus, and shed it for weeks, allowing strains that would otherwise die out to stick around, and kill any unprotected birds.
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16 .The study appears in the journal PLoS Biology.
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17 .Of course, none of this is reason to doubt the efficacy of vaccines.
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18 ."Vaccines have been one of the most important public health interventions.
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19 .And the most cost effective we've ever had.
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20 .And they're critically important in food chain security as well.
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21 .So vaccines themselves are fantastic."
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22 .But several imperfect vaccines for malaria are currently being tested.
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23 .If they're approved, he says, we'll need to use other measures, like bed nets, to block transmission, remembering that not all vaccines are a one-shot deal.
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24 .Thanks for the minute, for Scientific American 60-Second Science. I'm Christopher Intagliata.
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