The chances of an individual Covid-19 vaccine project producing a successful outcome are low, one of Britain’s leading immunisation experts has warned. “Science does not have a track record where most of our vaccine projects work,” Professor Adam Finn, of Bristol University said last week. “We have a track record where most of them don’t work.” Finn’s warning came as doctors and epidemiologists stressed how difficult it would be to contain the disease until people can be immunised against it. The crucial point is that if individual projects have low prospects of success, many different approaches will have to be taken to find one that does provide protection against Covid-19. “It is like the Grand National,” said Finn. “A lot of horses start off but only a few make it to the finishing line. And that is why we are going to need a lot of different vaccine projects to start off with – because only one or two are likely to make it to become fully fledged vaccines. This is not a one-horse race. “At present, I would estimate there are at least 60 Covid-19 vaccine projects that have started up or are in planning. But the more there are, the better things will be.” Most Covid-19 vaccine projects that have been announced so far have been for a type known as RNA/DNA vaccines. These involve taking genetic material from a virus and injecting into animals or human volunteers. This approach is quicker than other methods which typically involve creating pieces of a virus and using them to stimulate a person’s immune system against it. However, RNA/DNA vaccines – which are a recent development – have yet to be developed for use in human beings. “They are quicker to start up but we have much less experience with them compared with standard approaches.” All these projects have promise, Finn stressed, but most of those being launched to tackled Covid-19 were unlikely to work in the end. “The trouble is that we do not have a technology that allows us to be confident from the outset that a vaccine will be effective.” In addition, vaccines that do stimulate strong immune responses can also have adverse side-effects or may even make a disease worse. An example is provided by Dengue fever, which is spread by mosquitoes in Asia and South America. “A vaccine was developed to protect children against one type of Dengue,” said Finn. “Then it was found that it actually made them more susceptible to a second type of the disease.” For these reasons, vaccines have to be put through lengthy trials to ensure any dangerous side-effects are revealed. “We will have been cautious and not rush forward,” Finn added. On the other hand, it was possible that one of the projects would produce a vaccine that just sailed along, he said. It might turn out to be easy to manufacture, have no side-effects, produce a good immune response, while in trials it prevented volunteers from getting sick compared with those in a control group. For good measure,a factory would be ready to manufacture it. “In those circumstances, you would have a vaccine in less than a year,” said Finn. “But it is almost certainly not going to happen like that. There will be stumbles along the way.”