Covid-19 variants, monkeypox and now polio: you might wonder what else will be thrown at us in 2022. Last week in London, polio was detected in sewage screened by the National Institute for Biological Standards and Control (NIBSC), which has been surveilling the disease for decades as part of an international commitment to the World Health Organization. The latest screening and analysis with metagenomics indicates that this polio strain is derived from the oral polio vaccine (OPV) still used in some parts of the world. Some countries use live, non-infective, non-virulent polio virus for their inoculations, which can evolve to become infectious in some cases. So we now know there has been introduction and then transmission of one of these strains within London – though the exact cases have yet to be identified. Most people’s introduction to the concept of global health has been through Covid-19, and so it has come to be associated with broad population-wide measures such as mask mandates, closure of sectors, stay at home orders and limits on mixing. When hearing about polio and monkeypox, the response to Covid-19 might jump to mind. But this was a new disease, spread through respiratory mechanisms, for which there was no vaccine or established therapy, that threatened to bring about complete heathcare collapse. Covid-19 prompted a broad and extreme response given the threat of mass death. The response to polio is different. First, in the UK we have a safe and incredibly effective vaccine for polio, commonly referred to as IPV. This is administered as a jab by a trained medical professional. IPV is part of the standard childhood immunisation programme and, with all four doses, is 99-100% effective. There is no live virus in this vaccine. For this outbreak, the key steps are for public health teams to track down these cases in London to limit spread and stop further transmission, and for parents to be encouraged to check their children are vaccinated against polio. Vaccination is the best protection, but good hygiene measures are important too: polio is introduced into the body through the mouth and often from faeces (poo). Recent outbreaks of measles and mumps in Britain reveal how many children have not had their routine childhood jabs, and how complacency over vaccination has taken hold as memory of diseases such as whooping cough and tetanus fades. The emergence of polio in London also reminds us of the irreducibly global nature of health. Because of the relatively higher cost of IPV, and the need for decent health systems (including staff and equipment) to administer it, the live oral vaccine is still used in many places. Virus-shedding from someone recently vaccinated can spread to others. Mutations during transmission among unvaccinated individuals can result in a vaccine-derived poliovirus which can have the same negative impact as wild polio (ie paralysis). The Global Polio Eradication Initiative is now working to replace the use of OPV, given its risks, with at least one dose of IPV. While wild poliovirus is endemic in just Afghanistan and Pakistan, vaccine-derived polio cases are regularly identified in sub-Saharan Africa and other parts of the world. Contending with multiple infectious diseases at the same time is normal in most parts of the world. Cholera, plague, malaria and measles still circulate and cause illness and death, despite major global health efforts to support governments in managing them. We know about these recent polio cases because of surveillance: having routine testing in place meant that the underlying pathogen and its genetic sequencing were quickly detected and identified. And as part of the scientific advances made during the Covid-19 pandemic, surveillance has become better, especially in richer countries. However, it’s not the only reason we’re hearing more about outbreaks. We are actually having more outbreaks across the world, and diseases are spreading in unexpected ways. The underlying reasons are: more contact between animals and humans (when spillover events happen); animals being kept in unhygienic conditions (such as industrial farming); deforestation; increased urbanisation (people living close together); and connectivity (people travelling all over the globe). Hearing the news from London feels like a step backwards given how close the entire world has been to global polio eradication in recent years; however, we have managed polio outbreaks before, and it will be controlled again. The history of humanity is the history of various pathogens trying to disable and kill us – and equally the history of scientific and public health advances, and human ingenuity in staying ahead of them. Some humility in the face of infectious diseases and recognition of our global interdependence are always needed. Prof Devi Sridhar is chair of global public health at the University of Edinburgh