How vaccines are made, and why it is hard

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.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 or another to make the vaccine in question. Cells grown this way can be of many types—insect, human kidney, monkey kidney, hamster ovary—as can the resulting vaccines. These may be weakened or killed versions of the virus to be protected against, or live viruses of a different and less-dangerous sort that carry a gene or two abstracted from the target virus, or even just isolated target-viral proteins. The point is that the vaccine should introduce into the body, or induce that body to make, something which the immune system can learn to recognise and attack if the real target virus should ever turn up.