While you are sleeping, swarms of unicef logisticians around the world are busy mapping the worlds fridges.

The logisticians are part of the organisations efforts to ensure that a covid-19 vaccine if and when one is found to work and be safe can be delivered quickly to all corners of the world.

Most of the vaccines currently being studied involve a so-called cold supply chain, with temperatures that can go well below zero degrees celsius, down to -70c, though most need to be kept at between 2c and 8c. for a large part of the world, that is a problem.

Delivering a vaccine from a manufacturing plant into a patients arm requires the cold chain to remain intact for if it is not, the vaccine will break down and become unusable.

Much of the worlds attention has so far focused on the scientific advancements and setbacks in the race to find a safe and effective vaccine, which governments have supported with lavish amounts of public cash.

But less attention has been paid to the logistical hurdles the world faces once any vaccine is approved.

Experts agree there are two main problems. the first one is the cold supply chain, which poses problems for nations that do not have the required infrastructure to ensure the jabs stay cold.the second one is the training and management of staff that can administer the vaccine. the contenders in the final testing rounds are all injectable and require the assistance of qualified healthcare staff in order to be given safely.

Then come other obstacles. part of the challenge in manufacturing capacity is we don't have the ability to quickly switch and reconfigure the [manufacturing] lines, says prashant yadav, a supply chains expert at harvard university.

Unicef has been working with the world health organizations covax programme which aims to ensure equitable access to vaccinations for all countries in order to fine-tune the supply chain for the distribution of vaccines. gian gandhi, unicefs chief of market shaping and supplier financing, says 65,000 cold-chain fridges will be in place in lower-income countries by the end of the year.

Were not starting from scratch, he says, noting unicef has been helping conduct vaccination campaigns for about 2.5bn doses of other vaccines a year. but the covid-19 campaign could almost double that figure.

Any successful campaign would have to be phased: covax has been pushing to acquire vaccines that would in principle cover 20 per cent of a nations population, and 3 per cent, or workers in healthcare settings and other groups, would get priority access, with the remaining 17 per cent getting inoculated later.

Another hurdle will be the lack of flights during the pandemic, says pablo panadero, chief of unicefs transport centre.

[during march and april] we couldn't fly vaccines anywhere, with airports closed, he says. we had to fall back to chartering our own planes to deliver vaccines...given the volumes that we're talking about [now], it may be a viable solution.

We charter a plane that will land in 10 countries, well need to get the landing permit in all 10 countries and pull a lot of shipments to actually be able to reach some small countries, the so toms and equatorial guineas, he adds. its what enables the best reach.

According to mr panadero, unicef is talking to industry leaders and the international air transport association, which has said 8,000 cargo jumbo jets would be needed to deliver a single dose to the worlds 7.8bn inhabitants, compared with the roughly 400 that are still flying.

Dr gandhi says the efforts will push the boundaries of what is feasible everywhere.

For miriam ala, a vaccination expert with mdecins sans frontires, there are huge dispersion rates when it comes to vaccinating vulnerable populations, who tend to be highly mobile, especially in conflict areas. supply deals usually require a high percentage of the vials to be used, but in violent settings it is difficult to follow up or even convince patients to attend clinics. so structural challenges and violence can only compound the logistical hurdles.

She says covid-19 presents a so-called matrioska crisis, with each and every problem revealing another one.

For harvards dr yadav, solutions could come from working with other industries. what that could mean is in every country identifying what else is moving from lagos to northern nigeria, for example, that requires refrigeration and where we can piggyback on that, for example food companies, consumer product companies which have some cold chain, he says. it doesn't always meet the medical standards, but they have some capability and a good starting point to build from.

He adds that it might be possible some vaccines are more resistant to temperature changes than we think now, but monitoring would still be required till the moment it gets in the arm.

The knowledge would help construct more resilient supply chains in the future, covering other inoculations, but also insulin and cancer drugs.

It's ingenuity that'll help us solve this complex challenge, he says. ingenuity in how you create the logistics infrastructure that doesn't require setting everything up from scratch.