What will be the next pandemic?

“There are only three things that are inevitable in this world. Death, taxes, and flu pandemics.” – Dr. Allison McGeer, Former director of infection control at Mount Sinai hospital.

Although my generation has not before experienced what it is like to live through a pandemic prior to COVID-19, it is most likely something we will experience again in the near future. But this notion poses an important question; what type of pathogen will cause the next pandemic, and how may it differ to the one we are experiencing now?

Outbreaks of a particular pathogen are only classified as a pandemic when a certain set of parameters are met, including the inability to track the infection route case by case, when large populations of individuals are effected, and multiple nations and borders are crossed by the infection. A pathogen needs to meet a ‘checklist’ of properties to give it the best chance of reaching the above mentioned parameters, which gives rise to an important concept: not all pathogens will become pandemics.

One of the most defining properties of a pathogen that determines virulence is route of transmission. If you look over the last few centuries, the majority of outbreaks classed as pandemics involved influenza viruses such as H3N2 in 1968 and the infamous H1N1 in 1918, but also occasional occurrences such as Yersinia pestis in 1855. All of these viruses have one thing in common, they have a respiratory route of transmission.

This makes a lot of sense, as one of the easiest ways for pathogens to enter your body is through your respiratory tract. Once inside the respiratory tract, all that needs to happen is for the pathogen to withstand the environment that’s trying to get rid of it, replicate, and then be spread to other hosts through aerosolised droplets. Now consider that someone infected coughs on a crowded train; you’re looking at a lot of people who are at risk of being infected.

There is however an exception to this trend – the cholera pandemic of 1817-1824. This is a pathogen that is not transmitted through coughing, sneezing, etc, but instead is transmitted through faeces; in particular this pandemic started through contamination of water with infected poo. Nowadays, most people don’t usually die from a cholera infection due to the advancement in water treatment, disease treatment, and, for now, the effectiveness of antibiotics, but back in the 18th century the outbreak was thought to have killed around 2.5 million people.

So to answer the question: “What will be the next pandemic?”- no one really knows. Outside of it being highly likely to be caused by another Influenza or Coronavirus, there is still a very real danger of non-respiratory pathogens causing a devastating outbreak. On top of this, spread of urbanisation and a dangerously increasing global population size means that more areas around the world are being accessed and colonised by humans when they were previously untouched, increasing the risk of spillover events of new pathogens we have never even seen before.

Therefore, the most important question isn’t necessarily what the next pandemic will be, but when will the next pandemic come, and what can we do to prevent it?

Thanks for reading.