The earliest polio shot, for example, was superseded by an oral vaccine, which was easier to administer and lasted longer.

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Sabin developed an oral vaccine that would eventually supplant it.

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And last autumn the government was forced to withdraw an oral polio vaccine after it became clear it had been developed from serum which could potentially have been infected with BSE.

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Some very cool science is on the drawing board: a recombinant vaccine that pairs salmonella with a gene from, say, the organism that causes tuberculosis as an oral delivery system to stimulate the body's natural immunity to both bacteria.

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