You know how “pandemic” is just a word until you’re in bed delirious, feverish, shaking with chills, as one day blends into another? This was what happened to me in the fall of 2009. Unfortunately for me, I had been in hospital for routine surgery at the end of September. The nurse working closely over me a day or two after the surgery suddenly said, “Oh, I don’t feel good.” I told her to go home, and she vanished, but, sure enough, the next day I started feeling sick. The nurses figured I had caught a cold, and I was discharged. Once I was home, the fevers started. My husband took me to the hospital when I complained my chest felt weak. After many hours in an isolation room, I got a chest x-ray and a shot of toradol (which helped). The doctor told me they weren’t taking blood samples any more, as all influenza was coming back H1N1. She gently told me I had a mild case. I told her I had never been sicker from “just” influenza in my life. She told me cases were considered mild if the patient could breathe.

With this personal reason to take an interest, I became fascinated by the response to H1N1.

Remember, with avian influenza popping up occasionally and SARS a recent memory, there had been a huge amount of public health work on the possibility of a pandemic. But a lot of it was based on likely scenarios – a serious influenza, discovered in Asia, spreading rapidly around the world through person-to-person contact and international travel.

The big problem with epidemics is that they are unpredictable. They might be caused by any type of pathogen: bacteria, virus, prion, or something completely new. Existing pathogens might suddenly become deadly: SARS and the new coronavirus (which I recently wrote about in the Canadian Medical Association Journal) are from a virus family that normally causes “colds.” And pathogens can come from anywhere on the globe. While avian influenza (see my article on the new avian influenza virus in CMAJ)and SARS came from southeast Asia, H1N1 was first found in Mexico. The novel coronavirus is emerging in the Arabian peninsula.

Each pathogen has its own way to spread: food-borne, air-borne, water-borne. Some, like influenza, are incredibly contagious; SARS is less so. There is an inverse relationship with lethality and incubation: illnesses that strike quickly and kill many tend to disappear, for obvious reasons – the hosts don’t have time to spread them around. Instead, diseases with a 100% death rate (like HIV before recent drug regimens) tend to have a long period of incubation and illness; those that strike quickly like influenza have lower death rates.

Unlike H1N1, for most pathogens there are no vaccines. There is very good work being done on vaccines for certain pathogens. However, the development path for a vaccine is a long one, and often involves academic, public and private sectors.

Given this uncertainty, coupled with the unprecedented rate of international travel and the lack of strong public health systems in many countries, the chances of more pandemics during my lifetime are high. The worst-case scenario is an epidemic in a region that has remained off the international surveillance radar that simmers and flares up in the absence of a public health response. If it has a long incubation period (allowing travellers to take it around the world), a high death rate, and no vaccine, we’re in trouble.