Global health on the decline – rapid urbanisation threatens living space

As populations in developing countries continue to skyrocket, the world’s ability to control and prevent the spread of infectious disease will be severely strained.

By 2050, the world population is projected to hit 9.7 billion people, with two-thirds living in urban areas. This shift in lifestyle will inevitably result in pollution, leading to more health problems such as cancer and cardiovascular diseases.

As troubling as this may sound, current population trends are already changing the global health scene, which can mean bigger and more pressing issues.

Combine population growth with other pressures such as climate change and human migration, some parts of the world will encounter unparalleled levels of urban density. Megacities like Mexico City and Lagos are becoming more mainstream, and with that, there will be a rise in urban epidemic and a new age of infectious diseases.

Currently, the big cities in developing countries are pushing our ability to curb the spread of infectious disease. Ebola and Zika in urban communities are challenging our knowledge of how common diseases are spread. There is a need to reassess and update risk assessments for fatal pathogens with epidemic potential, safeguarding ourselves with the means to deal with urban outbreaks when they occur.

Theoretically speaking, cities should be able to handle infectious disease better than rural districts. Wealthy nations will naturally have more resources healthcare, finances and facilities wise. They will also have a stable electricity supply, access to refrigeration, sanitation and better supply-chain management to manage vaccines and other important medication.

In truth, low-income countries are inadequately resourced with lacking health systems. This explains why Ebola, a relatively not contagious disease spread quickly in West Africa, while it was curbed almost immediately in North America and Europe.

With lacking health systems, higher population numbers make it harder to curb outbreaks. Vaccination is the best and most cost-effective defence against infectious diseases, but challenges are surfacing. In the past, one in five children living in rural areas misses out on a full course of basic vaccinations. Now, many of these kids live in marginalised urban communities in the middle of cities, hiding in plain sight. This is a major blindspot and weak link in the restriction of urban epidemics.

This is almost unavoidable in Africa, as the population is projected to double by 2050, and quadruple by 2100 – from 1.2 billion to 4.4 billion. This population explosion will drive people towards the cities as desertification, land degradation, rising sea levels and famine continue to displace around 60 million between 2014 and 2020.

Regarding global health security, more people in less space places tremendous strains on already insufficient sanitation. This provides an abundant breeding space for infectious diseases and insect carriers. Concurrently, the sheer scale of cities will possibly stress vaccine supplies, drastically limiting abilities to respond to outbreaks. Angola is already suffering from a major urban outbreak of yellow fever in decades.

The scale and spread of infectious diseases can be unpredictable. In Angola, 8 million had to be vaccinated to stop the current outbreak. Thankfully, there were enough doses to go around, but this means dipping into supplies intended for future prevention. If another major outbreak happens in another major city, supplies might be seriously threatened.

Viruses are spread all the more quickly as people travel in and out of different countries. The yellow fever disease in Angola has already made appearances in Kinshasa, Beijing and Nairobi.

As cities grow and population, the risk and extent of outbreaks will rise, along with vaccinations needed to keep them in check. To avoid outbreaks, we should reduce the gaps in which infection can spread. This will include routine immunisation coverage and uncovering urban blind spots. Vaccination does also have to be continuously monitored to ensure that there is enough to counter worst-case scenarios.

Projected scenarios will need to be accurate in predicting scales of diseases, which might not always be linear. One prime example is Zika, where its full risks were only known after it spread to dense urban areas. Despite knowing this, it was too late for the thousands that were infected.

This article was originally written by Dr Seth Berkley, CEO of Gavi, the Vaccine Alliance for the Guardian.