In Depth

How the pandemics of the 20th century ended

Spanish, Asian and Hong Kong flu killed millions before medical advances and social measures brought them to a close

The number of confirmed coronavirus cases worldwide is nearing one million, a troubling milestone in a pandemic that has caused significant upheaval in people’s lives across the globe. 

As experts try to predict when the figures might level off and finally decrease, The Week looks back at pandemics of the 20th century.

Spanish flu

In 1918, as the First World War was coming to a close, a devastating flu virus spread across the globe, killing somewhere between 50 million to 100 million people in the deadliest flu pandemic of all time.

Despite the staggering death toll, the outbreak, which became known as Spanish flu, revealed “just how many lives can be saved by social distancing”, Quartz says, noting that “cities that cancelled public events had far fewer cases”.

“Just as the outbreak was unfolding, Philadelphia threw a parade with 200,000 people marching in support of the World War I effort; by the end of the week, 4,500 people were dead from the flu,” the news site adds. “Meanwhile, St Louis shuttered public buildings and curtailed transit; the flu death rate there was half of Philadelphia’s.”

Problematically, the virus came with not one peak but two – the first in June and July, followed by a second even deadlier wave in October and November. But by the summer of 1919, the flu pandemic had come to an end, “as those that were infected either died or developed immunity”, History.com writes, as a vaccine had not been developed.

Asian flu

Another major 20th-century pandemic was so-called Asian flu, which took hold in 1957 and caused an estimated one million to two million deaths worldwide. As Encyclopaedia Britannica notes, the 1957 Asian flu outbreak is “generally considered to have been the least severe of the three influenza pandemics of the 20th century”.

New Scientist reports that the 1957 pandemic was “triggered by the hybridisation of human H1 flu with flu viruses from birds which carried another surface protein, H2”, which created a virus “more lethal than the then-circulating H1 strains because no human had ever encountered the H2 protein before, and so lacked any immunity to the new strain”.

The disease spread rapidly and was reported in Singapore in February, Hong Kong in April and the coastal cities of the US in the summer of 1957, says CDC.

However, a vaccine was developed by the autumn and rolled out worldwide, while the availability of antibiotics allowed doctors to treat people with secondary infections, limiting the spread and mortality.

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Hong Kong flu

The third influenza pandemic to occur in the 20th century, so-called Hong Kong flu, came in 1968. It was an outbreak of influenza A subtype H3N2, which is suspected to have evolved from the strain of influenza that caused the 1957 pandemic.

As Britannica notes, Hong Kong flu “caused illness of varying degrees of severity in different populations”, adding: “For example, whereas illness was diffuse and affected only small numbers of people in Japan, it was widespread and deadly in the United States.”

Although a vaccine was developed, it became available only after the pandemic had peaked in many countries, and somewhere between one million and four million people died from the virus. 

But Medicine Net notes that “instead of peaking in September or October, like pandemic influenza had in the previous two pandemics”, the 1968 outbreak “did not gain momentum until near the school holidays in December”.

“Since children were at home and did not infect one another at school, the rate of influenza illness among schoolchildren and their families declined,” it says.

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