How will the world vaccinate seven billion?

Teams across the world are working to develop a vaccine that will be effective against Covid-19. But away from the hightech science of finding a winning formula, what about the logistics of rolling out a vaccine to seven billion people worldwide?

Matthew Duchars, chief executive of UK's Vaccines Manufacturing and Innovation Centre (VMIC), says: "It's important, globally, to be able to produce these types of vaccines quickly and effectively." "To use an analogy - it's like baking a cake at home. You spend hours preparing the perfect cake and now you've got to bake 70 million of them and they all have to be perfect."

That's putting it mildly. Ultimately, the human race will need to make billions of doses of several types of Covid-19 vaccines. They will all have to be manufactured, distributed and administered across the globe.

The international vaccines alliance - Gavi - is urging countries to start thinking about vaccine rollout now. But it's not easy to get international co-operation, because many rich countries are doing bilateral deals with drug companies to make sure they can secure supplies of the magic formula.

Seth Berkley, Gavi's CEO, says one of the biggest hurdles he's facing is "vaccine nationalism". "If you have large reservoirs of virus circulating in surrounding countries, you can't go back to your normal trade, travel or movement of people. It's really important to have that mindset: we're not safe, unless everybody is safe."

As well as trying to make sure developing countries get access to the right vaccines, Mr Berkley has to think about the more prosaic aspects of vaccine roll-out, including whether or not there are enough glass vials in the world. If glass vials are a potential problem, then so are fridges, since most vaccines need to be kept at low temperatures.

Prof Toby Peters, an expert in cold chain logistics at Birmingham University, is helping Gavi think about how they can maximise existing refrigeration capacity in developing countries. "It's not just a vaccine fridge, it's all the other pieces too: the pallets which move it in planes; the vehicles that move it to local stores, and the motorbikes and the people who take it into the communities."

To make the vaccine roll-out more manageable, countries will have to work out who to prioritise in their populations. The scientists think some kind of vaccine will be found. But many of them are kept awake at night by the sheer scale of what needs to be done to get it to billions of people.