Science in Medicine

The Spanish Flu of 1918

Kate Roach

March 2003
Updated December 2005

Within a four-year period, the gory battlefields of the First World War claimed the lives of 15 million people. An armistice finally put a halt to the killing on the 11th hour of the 11th day of the 11th month of 1918. Yet many more soldiers would meet their deaths on their return home. An invisible enemy was on the rampage the world over – the flu virus. In just one year, somewhere between 50 and 100 million people died from the flu. Today, virologists are warning us that this is certain to happen again – and we still don't have a cure.

A fatal strain of bird flu has recently infiltrated human populations across the globe. At the moment scientists believe that this strain doesn't easily transmit from human to human, but all eyes are peeled just in case the situation changes. So what is it that turns flu into such a virulent killer?

Flu or the common cold?

A cheese grater has been at your throat, your head is stuffed with cotton wool and you feel like you've recently been through an army assault course. Do you really have flu, or is it just another cold? The difference is subtle but important. The common cold is a minor viral infection of the nose and throat. About 200 different viruses are known to cause colds. The most common is the rhinovirus, of which there are over 100 varieties. The sheer number of viral agents makes it difficult if not impossible to produce a single effective vaccine. What we call a cold, is not one disease, it is many. Typically, adults get two to four colds a year, while children get six to eight.

Flu is an altogether different beast. The symptoms can be similar to a cold but they are generally more severe. Strictly speaking, the term flu (shortened from influenza) refers to an infection caused by the flu virus. There are two types of major significance to humans – influenza A and influenza B. Flu is usually an illness of fairly rapid onset. The major symptoms are high fever, headache, muscle aches and pains and general listlessness. A cough, runny nose and sore throat are often part and parcel of a bout of flu, but they are not always as prominent as they are in a cold.

Most people don't think of flu as a potentially fatal condition, but it can be that serious. Those at highest risk of a fatal dose of flu are the elderly, the very young and those who are already sick with other conditions.

The great flu pandemic of 1918

John Oxford is Professor of Virology at St Barts and the Royal London Hospital. He believes it's important we learn some lessons from the flu pandemic (global epidemic) of 1918 because it's certain to happen again. He explains just how vicious it was:

'You can ask anyone about the bubonic plague, and they'll say, ah yes, the plague killed a third of Europe. But it still didn't have the impact of the 1918 flu, because bubonic plague killed people over periods of 10, 20, 40, 50 years. Influenza in 1918 killed 50 million souls in a period of one year, and that's why, to my mind, it's the biggest outbreak of any infectious disease the world has ever known.'

John Oxford has been trying to understand why the 1918 flu was such a killer. What was different about it compared to normal seasonal strains of flu?

The burning question for John Oxford is why the 1918 flu was such a killer. What was different about it? Doctors and pathologists of the period had seen flu before, but they knew they were dealing with something unique in 1918. On initial infection, the symptoms were much the same as any other flu, but a proportion of people who succumbed to the virus didn't improve as expected on the fifth or sixth day, in fact they got worse.

Doctors and pathologists of the period had seen flu before, but they knew they were dealing with something unique in 1918. On initial infection, the symptoms were much the same as any other flu, but a proportion of people who succumbed to the virus didn't improve as expected on the fifth or sixth day, and in fact they got worse.

Doctors noted an unusual feature of the disease that spelt grave danger. Those patients who developed a lavender-grey hue over their face and ears, or heliotrope cyanosis as it is called, were facing imminent death. Pathology reports from 1918 describe very distinctive changes in lung tissue that were the likely cause of death in many victims and probably contributed to the heliotrope cyanosis. Healthy lung tissue is like a sponge filled with air, but in flu victims the lungs were filled with fluid containing red blood cells and immune cells – causing death by asphyxiation.

Another unique feature of the 1918 flu pandemic was the age profile that it attacked. The first wave of flu, at the start of 1918, was largely only fatal in the very young and the elderly. In the middle of 1918 there was a sudden change and the virus began killing healthy adults between the ages of 25-40. And then by 1919 the virus had reverted back to its old ways, targeting the very young and the elderly. This strange pattern of virulence is one of the mysteries of the great flu pandemic of the First World War.