Epidemics and pandemics

Paris, May 1918. The French writer Guillaume Apollinaire is sitting in a café reading the paper. It’s mostly about the First World War, which has been going on for almost four years, but his attention is drawn to another article. This is talking about a new disease that has broken out in Spain. “The king, the prime minister, and several other ministers have been taken ill. They are suffering from a mysterious sickness that has spread throughout Spain and has affected 30 percent of the population.

The disease is not considered to be dangerous. But that’s not true. Definitely not true. Half a year later, Apollinaire himself gets infected. In November, he dies of the new disease.

Now people are calling it Spanish flu, and during the two years between 1918 and 1920 it will take the lives of 50 to 100 million people all over the world. Apollinaire dies just two days before the end of the First World War which, in comparison, results in about nine million deaths. So the Spanish flu kills many times more people than history’s bloodiest war so far. A disease that is spread when people infect each other is called an infectious disease. If the disease spreads widely in a population over a short time, the outbreak is said to be an epidemic.

Often viruses or bacteria are the causes of infectious diseases. One single virus that enters a human body can quickly grow in number into several billion copies of itself. Some types of viruses cause indications of illness, symptoms, such as sneezing or coughing. The droplets in a single sneeze can contain hundreds of millions of viruses. If another person is nearby, it’s easy to breathe in a tiny droplet from the sneeze.

Or a droplet may end up on a door handle. The next person who opens the door might carry away the virus on their hand. If they happen to touch their face, the virus might enter their body. Yet another person is infected. New viruses are emerging all the time, and some of them are leading to epidemics that affect very many people in many countries.

This is called a pandemic. Some pandemics in history have been extra serious, with millions of deaths. But how can a disease spread so rapidly? Here is the first person who is carrying a new virus. They infect two people.

Those two each infect two more people. We’re up to seven infected. These four infect eight people. These eight infect 16. The total is now 31 infected.

That’s still not that many, and at first the infection spreads slowly. But the more people infected, the faster the infection spreads. Soon it’s 31 to 63, 63 to 127, 127 to 255, and so on and so on and so on and so on... The disease spreads faster and faster. When one million people are infected, together they may be able to infect two million more people during the course of a day or two.

But sooner or later, the disease starts to spread more slowly. Usually, the bodies of those who have had a virus disease develop a defense against the virus: they become immune. Then they can't get infected again by the same strain of that virus, and they can't spread it again. So when enough people in a population have been infected, the disease spreads more slowly. In the best case, a vaccine can be developed which can prevent people from becoming infected.

If many are vaccinated the spread of infection can be stopped. There are vaccines against many serious diseases such as tuberculosis, polio, and measles, but there are usually no vaccines against brand new viruses. Scientists are working as hard as they can to develop new vaccines. But this takes time, and it’s nearly impossible to get a vaccine ready before a pandemic has extended across the world. There was no vaccine against Spanish flu, however the spread of this disease slowed down by itself.

The virus still existed, but the pandemic it caused was over. By that time more than one in four people had been infected. Guillaume Apollinaire was one of those who died, and between two and five percent of the world's population died also. That makes Spanish flu one of the deadliest pandemics in history.