The battle against polio provides a good illustration of the task we face. The disease is caused by a virus that mostly affects children, and can lead to irreversible paralysis and sometimes death. The eradication effort has been a huge success, with cases dropping from 350,000 a year in 1988, to just 33 in 2018.

The virus that causes polio was endemic in 125 countries in 1988, but today remains so in just two, Afghanistan and Pakistan. However, the virus is highly infectious. A single infected child could lead to hundreds of thousands of new cases a year around the world. So it must be completely stamped out, just as smallpox was eradicated in 1980. We could incentivise the push to eradication by increasing the funding, safety and resources for staff working in these incredibly challenging areas. In northern Nigeria, dozens of healthcare staff working to vaccinate and eradicate polio have been killed by gunmen thought to be members of Boko Haram. We will also need to improve the understanding of the safety of the polio vaccine to increase uptake. In Afghanistan, for example, we will need to counter the spread of anti-vaccine propaganda. In all countries, we will improve disease surveillance and data collection to better monitor the progress of eradication, and work to address people's basic needs – fresh water, food supply – in remote areas where the virus clings on.

The effort to eliminate the polio virus has prevented 1.5 million deaths, and 18 million cases of paralysis.

In 2019, the WHO made a list of things it considered major health threats, including the problem of what it diplomatically calls "vaccine hesitancy" – which is at least as big a problem in rich countries such as the US, the UK and Japan as it is in poorer countries. The drop in the numbers of people willing to be vaccinated was a major concern even before coronavirus; it's that much greater now, in the Covid era.