t would only cost $50bn to ensure 40% of the world’s population is vaccinated by the end of the year, and 60% by the first half of 2022. This is a recent estimate from the IMF, the latest institution to join a chorus of voices calling for a global vaccination programme to bring Covid-19 under control. The IMF has highlighted the economic benefits of global vaccines, which would be huge. But there is another powerful reason for a worldwide campaign. Vaccinating the world will be crucial if countries are going to act together to confront the climate crisis, which will require many of the same things as delivering vaccines: resources, innovation, ingenuity and a true partnership between rich and developing countries. The Cop26 climate conference in November will be an opportune moment for building this partnership. But to do so, rich countries need to deliver on their early promises to deliver global vaccines. As it stands today, vaccine access is deeply unequal. The US is starting to vaccinate children, even as health workers and elderly people are waiting for shots in most of the world. At the end of April, less than 2% of the population of Africa had been vaccinated, while 40% of the population of the US and 20% of the population of Europe had received at least one dose. India, one of the largest vaccine manufacturers in the world, has fully vaccinated 3% of its population, and is still in the middle of a nightmarish second wave that has forced the country to stop exports of all vaccines. It was clear for some time that this was where things were heading. Despite all the talk of solidarity at the beginning of the pandemic, rich countries built sufficient capacity to produce only enough vaccines for themselves and then proceeded to corner the world’s supplies. By March, high-income countries accounting for 16% of the world’s population had bought up 50% of vaccine doses. As of this month, only 80m of the 2bn vaccines promised to the world’s poorest through the ACT accelerator, a partnership including the UN-backed Covax scheme, have been delivered. The reason? A combination of insufficient donor funds and competition for vaccine doses from the richest countries, who can afford to pay high prices if needed, and who are planning to stockpile millions of extra doses for the future. The Bill and Melinda Gates foundation estimates that rich countries will have up to a billion extra doses on hand by the end of this year. These inequities were mirrored by what happened with economic policy. While rich countries borrowed massively and spent more than 20% of GDP to help their populations ride out the crisis, poor countries could afford to spend only 2% of GDP. An estimated 100 million more people are now living in extreme poverty compared to the start of the pandemic. Developing countries contemplating lockdown are caught in a double bind between economic disaster (in India, for example, the first lockdown cost the country almost a quarter of its GDP) and overflowing morgues and mortuaries. The catastrophic moral failure on the part of rich countries to help poorer nations can only reinforce the strong suspicion in much of the developing world that, despite talk of global cooperation and shared fortunes, when push comes to shove it’s everyone for themselves. This could be devastating for global efforts against the climate crisis. The success of Cop26 depends in part upon larger developing countries such as Bangladesh, China, India, Indonesia, Mexico, Nigeria and Pakistan committing to sacrifices that will only pay off if countries such as the US, UK, Germany, France and Canada can be relied upon to stick to their own commitments. By agreeing to cut CO2 emissions, these developing countries will potentially curtail their own growth and perhaps even have to give up equipment that protects them from an already changing climate in the short term, such as cheap, polluting air conditioners. This sacrifice will only pay off if rich countries respond by cutting their own emissions so that worst-case scenarios can be avoided. Without everyone doing their part, we’re effectively rearranging the deckchairs on a sinking ship. In the aftermath of Covid-19, these countries may wonder what guarantee they have that when the next disaster strikes – and domestic pressures mount – rich countries won’t abandon their commitments. Trust, therefore, is key. Even if rich countries made binding commitments to domestic climate policies at Cop26, this would be unlikely to get developing countries to sign a demanding agenda. There is a strong and entirely justified perception that the world’s poor are being asked to make sacrifices to atone for rich countries’ past sins of careless growth. The fact that these countries have now shown they care little about the wellbeing of poorer nations obviously does not help. Developing countries will, quite reasonably, demand to be compensated for the more onerous choices that Cop26 demands of them. Research by colleagues in our MIT lab J-PAL, which runs the King Climate Action Initiative, demonstrates that this kind of conditional compensation works: in Uganda, paying landowners to not cut down trees has curbed deforestation and reduced carbon emissions at a cost of less than $1 per tonne. Researchers are studying dozens of other policy innovations that could work across the world – from emissions trading to incentives to reducing crop burning. These schemes only work if developing countries trust they will be paid compensation. Such promises have been made: advanced economies have formally agreed to raise $100bn per year for the Green Climate Fund to address the pressing mitigation and adaptation needs of developing countries. But at the moment, both developing countries and their citizens are questioning whether they can trust them to stick to their part of the bargain. How do we rebuild trust quickly? Investing now to vaccinate the world is a chance to repair the damage done in the past year. The IMF price tag of $50bn is a rounding error compared to what the US and Europe have already spent on Covid relief. Of course, money won’t be enough: vaccines will need to be produced, stored and delivered. Pharmaceutical companies will, somehow, need to be persuaded to share their profits drawn from intellectual property; supply chains for all the ingredients to make the vaccines need to be streamlined to avoid bottlenecks. Then, a tremendous effort in developing countries will be required to efficiently administer the shots. There is some faint indication that the world is heading in the right direction: the G20 countries just acknowledged “the importance of addressing the ACT-Accelerator funding gap, in order to help it fulfil its mandate”. Covax was recently able to sign an agreement to buy 200m doses of Johnson & Johnson vaccines. The US and the EU have agreed to donate relatively small numbers of unused jabs (80m and 100m, respectively). The Biden administration signalled it would be open to a waiver of patents on Covid-19 vaccines, which will undoubtedly put some fire under the pharmaceutical companies to find partners and produce more. And the heads of the World Trade Organization, World Bank, IMF and World Health Organization have jointly endorsed the IMF plan. But this is all too little and too slow. Succeeding in this vaccination effort is our chance to show that the talk of a common community and a shared destiny is more than just words. To prove that it is there, let’s start with vaccines. Abhijit Banerjee and Esther Duflo were the joint winners of the 2019 Nobel prize in economic sciences