Statistics aren’t everyone’s cup of tea. They can be complicated, bad actors can cherry pick what they like, and sometimes they can tell us things we don’t want to know.

For example, a new statistical study has discovered that large pandemics are much more common than you might expect. In fact, the team found that a pandemic with a similar level of impact to COVID-19 has around a 2 percent probability of occurring each year.

When you add that up across an entire lifetime, this means we each have a 38 percent chance of experiencing a big one at least once, and the odds look set to get worse with time.

“The most important takeaway is that large pandemics like COVID-19 and the Spanish flu are relatively likely,” said Duke University global environmental health researcher, William Pan.

The team looked at the historical record of epidemics from the year 1600 until now. They found 476 documented epidemics, around half of which had a known number of casualties. About 145 caused less than 10,000 deaths, while 114 others we know existed, but not the number of deaths.

Importantly, infectious diseases that are currently active were excluded from the analysis – so that means no COVID-19, HIV, or malaria.

The team used detailed modelling with a generalized Pareto distribution to analyze the data, finding that the yearly number of epidemics is immensely variable, and an extreme epidemic like the Spanish flu of 1918-1920 had a probability of occurring somewhere between 0.3 and 1.9 percent each year over the last 400 years.

“The slow decay of probability with epidemic intensity implies that extreme epidemics are relatively likely, a property previously undetected due to short observational records and stationary analysis methods,” the team writes in the paper.

But this isn’t a steady probability either – it’s growing.

In the last 50 years, we’ve seen increasing levels of new pathogens spreading through humans. SARS-CoV-2 is the most obvious example, but even in the last few decades we’ve had swine flu, bird flu, Ebola, and many, many more.

“Together with recent estimates of increasing rates of disease emergence from animal reservoirs associated with environmental change,” the team writes, “this finding suggests a high probability of observing pandemics similar to COVID-19 (probability of experiencing it in one’s lifetime currently about 38 percent), which may double in coming decades.”

So, even while we are recovering from a current outbreak, it’s important that we don’t assume we won’t see another life-changing pandemic soon enough.

In fact, if we play our cards right, our response and resources for COVID-19 can prepare us for the next pandemic.

“This points to the importance of early response to disease outbreaks and building capacity for pandemic surveillance at the local and global scales, as well as for setting a research agenda for understanding why large outbreaks are becoming more common,” Pan said.

If statistics have anything to do with it, the next pandemic is coming – let’s just hope we don’t forget the past.

The research has been published in PNAS.

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