NINE VACCINES against covid-19 have already been approved in one jurisdiction or another, with many more in various stages of preparation. That this has happened within a year of the illness coming to the world’s attention is remarkable. But it is one thing to design and test vaccines. It is another to make them at sufficient scale to generate the billions of doses needed to vaccinate the world’s population, and to do so at such speed that the rate of inoculation can outpace the spread and possible mutation of the virus.

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Broadly, there are two ways of making antiviral vaccines. One, tried and trusted, involves growing, in tanks called bioreactors, cell cultures that act as hosts for viruses which are then used in one way

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