The 1918-1920 H1N1 Influenza Pandemic "Spanish flu"

Updated: Jun 5

Article from historian and political scientist Dr. Rolf Tanner for Prime Re Solutions


Of all the pandemics and epidemics of modern times, the 1918-1920 H1N1 Influenza (“Spanish flu”) was the most fatal – about one fourth of the then global population of 1.9 bn people was infected, and the numbers of total fatalities range anywhere between 17 and 100 million, with a growing consensus estimate around 50 million (3.5 – 21 % mortality rate, with 10,5 % as the consensus). This puts the Spanish flu among the “mega-death” human disasters of modern times, whether man-made or natural: the 1816 “Year without summer” famines as a consequence of the Krakatoa volcano eruption in Indonesia, the combination of uprisings and natural disasters during the Taiping Rebellion period in China 1854-1860 (10-30 million), the famines as a consequences of El Niño phenomena 1877-1881 (up to 50 million mostly in India, China, Egypt and Brazil) and 1899 (up to 10 million mostly in India), the First World War and its aftermath (20 million), the Second World war (55 million) and Mao Zedong’s failed Great Leap Forward and the ensuing famines 1958-62 (50-60 million fatalities).


The designation as “Spanish flu” relates to the fact that in Europe and US, wartime censorship prevented the media from reporting on the flu pandemic – not so in neutral Spain where press freedom continued and media freely reported on the disease. This created the erroneous impression that Spain was particularly affected, or that Spain was the origin of the pandemic.


The shape and features of the pandemic


The pandemic evolved in three major waves: a first wave in spring 1918, with high infection, but comparatively moderate death rates; a second wave starting late August 1918 simultaneously in France, Western Africa and the East Coast of the US, which proved to be much more deadly; a third, more localised wave in spring 1919 and, possibly, a fourth wave in early 1920. The existence of a fourth wave is sometimes disputed.

Death rates in the UK 1918-1920, source: Wikipedia

Death rates varied highly across countries, and within countries. They were highest in some European colonies, though fatalities are sometimes highly disputed here. Fatalities due to the influenza are difficult to be separated from fatalities from other causes as a result of on-going wartime circumstances, internal population movements, and revolutionary upheaval: e.g., Russia was in the midst of a devastating revolution and civil war, but reported comparatively few fatalities from the flu.

Source: Wikipedia, Angus Maddison and others

The Spanish flu was marked by a number of oddities that makes it to stand apart from other pandemics experienced from the 19th to the 21st century. One key differentiator is the high mortality among young adults, particularly pregnant women. Flu pandemics usually produce the highest mortality rates among the very young and the elderly (u-shaped mortality distribution). But with the Spanish flu, 99 % of US fatalities were below

Mortality distribution among age cohorts 1918 vs. normalised 1911-1917, source: Wikipedia

65 years in 1918-1919 and 92 % for the whole period of 1918-1920. Among the very young (5-15 years), infection rates were higher than normally with flu infections (25 % in 1918-1920 in comparison to 11 % for the normalised period). But mortality in this group was lower than with other pandemics. Overall, it would appear that the 1918 H1N1 virus was not more contagious than other flu viruses, but was much deadlier. The 1918 pandemic showed a distinct w-shaped mortality distribution, with young adults impacted moderately high. Among infected pregnant women in the US, the death rate ranged from 23 to 71 %. Of those surviving the infection, one quarter lost their unborns.


There are no exhaustive medical rationalisations why the Spanish flu hit young adults so strongly. Some analyses show that the virus triggered a cytokine storm that ravaged the stronger immune systems of young adults. Yet, other studies dispute this, highlighting that viral infections in military hospitals with many young men was not more aggressive than with viruses from previous flus. Also, the second wave of autumn 1918 proved to be much more deadly to young adults than the first wave which had produced a more normal mortality distribution pattern (the very young and elderly). This has led to assumptions that the virus mutated between the first and second wave, though there is no hard evidence for this. The third wave was still very deadly to young adults though somewhat less than the second wave.


Non-medical rationalisations for high mortality among young adults are associated with wartime circumstances: overcrowded military hospitals with poor hygiene furthered the spread of the virus. Moreover, the peculiarities of military life facilitated the spread of deadlier strains of the virus: In normal civilian life, severe cases of infection tend to stay at home while those infected with less severe strains go out working. This leads to the isolation of more severe strains of the virus while the milder varieties can spread easily, eventually contributing to the abatement of the pandemic. Military life, however, turned this pattern onto its head: less severe cases remained in the trenches and continued to fight while more severe cases were transported to military hospitals in the rear. These made the less severe strains to stay isolated while more severe strains could proliferate easily. However, while the peculiarities of military life may partly explain the high death rate among young adults, they fail to do so where civilian circumstances continued to prevail, i.e., in the US and most other parts of the world outside Europe.


Another oddity of the 1918 Spanish flu was that three waves of outbreaks materialised over the course of one year. The flu usually sets in with the advent of the colder periods of the year. Yet, the 1918 pandemic had its first outbreak in late winter, to be followed by a second wave in mid-summer which terminated at the end of the year. The third wave was again in late winter/early spring.


Infections often saw a rapid clinical course, with a mere 24-48 h between hospital admission and death. The illness progressed to extensive organ involvement, primary viral pneumonia, to be followed by bacterial pneumonia and lung empyema. Many deaths occurred as a direct consequence of the latter. Bacterial pneumonia is a common secondary infection associated with influenza in some cases.


Treatment was limited to supportive care. In 1918, neither vaccines nor antibiotics were available (flu vaccines were only discovered in the 1940s, and antibiotics only in 1928 (penicillin)). Medical knowledge about the flu spread unevenly: it seems that the medical professions in Latin America became aware of the new virus only when the second wave struck. The flu was sometimes misdiagnosed as dengue fever, typhoid or cholera. There were several attempts to come up with “vaccines”. Although they proved largely ineffective, they may have helped to lower bacterial infections.


In terms of medication, doctors used aspirin, quinine, opium, camphor, alcohol, wet packs, cinnamon and turtle soups; in addition to this prescribed cures, folk cures were widespread. For a while, aspirin was said to be effective which led to oversubscriptions and in some cases to overdoses. However, it is an urban legend that widespread aspirin poisoning inflated the death rate.


The origins of the virus


There is no clinical sample of the H1N1 virus surviving, and its etiology is unknown (flu viruses could only be isolated in 1931, leading to the development of vaccines). Maybe it was accompanied by a strain of pneumonia bacteria which would explain the high incidence of bacterial pneumonia. There are essentially three theories about the origins of the virus:

  • First cases in Europe emerged in late 1917/January 1918 around a British military hospital in Flanders. It was adjacent to a pig farm, and the hospital inmates were fed large amounts of poultry brought in from neighbouring villages. The combination of overcrowded human quarters on the one hand and porcine and avian habitats on the other hand are classical breeding grounds for flu viruses. According to some studies, milder variants of the virus may have circulated among the troops in Western Europe for a while, with mutation into a deadlier form occurring in Flanders.

  • Another source of the virus has been identified in overcrowded military training camps in Kansas where first cases appeared in January 1918. This theory posits that the etiology of the virus was indigenous to the US.

  • A third source could have been China. The Middle Empire was relatively mildly affected by the 1918 influenza which led to the theory that milder variants of the virus had been circulating for a while immunising a large part of the population. China – which had declared war on Germany and its allies in late 1917 – sent a labour corps to the Western front. It travelled to Europe via Canada and the US. Members of the labour corps might have brought the virus to the US where it mutated into a deadlier form, starting infections in Kansas. In 2016, research by Chinese academics strongly denied that the virus originated in China.

The spread of the virus was definitely facilitated by the wartime circumstances. Large amount of troops were moved around: Between March and July 1918, one million US troops disembarked in France. Sanitary and hygienic conditions in military camps, and above all at the frontlines were extremely poor. Millions of men were living squalid lives in wet, damp trenches where infectious diseases ravaged. Food was nutrient-poor and in short supply, alcohol abuse rampant and sleep deprivation common. After the war ended, 800,000 US and 1,2 million French colonial and British Commonwealth troops were ferried home within a few months, possibly contributing to the third wave of the pandemic. The death toll due to the flu was high among the forces – the American Expeditionary Force suffered 53,000 combat and 63,000 non-combat fatalities (sickness, accidents) between July and November 1918. Influenza was the biggest contribution to non-combat fatalities.


In Germany and Austria-Hungary, civilian population suffered from a naval blockade that curtailed food imports and led to a deterioration in the quality and diversity of food diets. In late 1918, the average intake for an industrial worker in Germany was down to 1,700 calories per day (2,200 calories are normally regarded as a minimum for an industrial worker). Malnourishment among the poorer strata of the population was quite common (especially women and children). In Eastern Europe, already weak health infrastructures collapsed under the double impact of war and revolution.


Government actions


Before the First World War, health was mostly the prerogative of local authorities. There was no international organisation equivalent to today’s World Health Organisation (WHO), and most countries did not have a ministry of health though they usually had promulgated laws and regulations that dealt with disease and epidemic management (though more often related to animal diseases like foot and mouth). Likewise, hospitals were mostly in the hands of local authorities or – predominantly in Catholic countries – churches and monasteries. In many European countries, public medical resources had been depleted by the war: in 1918, an estimated 50 % of French doctors under 65 had been seconded to service with the military, leaving large parts of the hinterland medically underserved and unattended.


The media played an awkward role. Initially, wartime censorship prevented reporting about the flu. After the end of the war, censorship was lifted, making many newspapers to indulge in sensationalism to relish won-back liberties, particularly in the US. The flu became a popular topic, often mixed up with fears of Bolshevist subversion. The flu and Bolshevism were sometimes described as “diseases” and the two sides of the same coin. Headlines caused anxiety, panic and confusion. Public knowledge and instruction about the flu remained generally poor, and fake news circulated widely and wildly, such as that German or Bolshevik spies inserted germs into the water supply to spread the flu.


In Europe, public reaction was more restrained. The immediate war aftermath, economic difficulties, and on-going political turmoil competed for public attention. The flu was only one among many “bad news”, and there was greater equanimity to absorb them quiescently. There also was a general mental exhaustion after the war effort.


No country save Japan adopted a national strategy to combat the flu. Japan imposed a nation-wide immigration ban. It was local, county or state authorities that implemented non-pharmaceutical interventions to prevent the spread of the pandemic. The measures were similar in most locations: school and church closings, a ban on public gatherings, travel bans and confinement orders. In the US, port cities quarantined new arrivals. In some locations, authorities also closed shops, or limited their opening hours, but were often forced to revoke these restrictions after popular protests. In others, shops began to develop home delivery services which, however, were quickly abandoned again after the flu passed.


In a number of cities, authorities mandated the use of disinfectants in streets, staircases and public transportation. In San Francisco and Seattle, the wearing of masks in public was made mandatory. Emergency hospitals were opened in a large number of cities in the US and Europe, the latter case sometimes operated by the military or medical staff returned from the war.


A later study of the non-pharmaceutical interventions taken by 43 US cities showed that cities that took early and radical measures had a (sometimes much lower) mortality rate than those that reacted late or not at all. There is consensus that the outbreak of the third wave of spring 1919 was at least partly due to premature revocation of school closings and other non-pharmaceutical interventions.


Economic and social impact


There are no systematic analyses on the impact of the Spanish flu on economies, either national or international. Effects are very difficult to disentangle from other factors that were simultaneously at work, i.e., the First World War and subsequent tremors associated with demobilisation, the end of government-funded armament procurement, and political turmoil. The economic growth rates of the four largest economies for 1918 to 1921 (US, UK, France and Germany) show wild gyrations which undoubtedly embed effects from the flu, but are also nationally idiosyncratic and reflect very different economic paths after the end of the war.

GDP growth in %, source: Angus Maddison

During the First World War, many government introduced war economy measures of which many remained in force beyond the end of hostilities, such as price controls, or the rationing of food. This has contributed to dampen adverse effects from the non-pharmaceutical interventions and high death rates, but also obfuscate the precise identification of the impact non-pharmaceutical interventions had on the economic performance.


The available evidence about the economic impact is mostly anecdotal and localised. In Little Rock, Arkansas (USA), it was estimated that retail business was reduced by 40 to 70 % during the second wave of August 1918, with groceries about one third lower. In Tennessee and Kentucky, coal mines reported a production decline of 50 % in October 1918. Some mines closed operations. Also the lumber industry reported drastically lower sales. The only sector seen as benefiting were drug stores.


The impact on the workforce and on manpower was significant. Telephone companies in the US Midwest urged their customers in autumn 1918 to avoid unnecessary calls as about one fourth of staff was on sick leave. In Geneva, Switzerland, the city government reported in late 1918 that a number of enterprises had virtually closed shop as nearly 80 % of staff was ill. Similar absent rates among staff were suffered by German department stores in Düsseldorf and Cologne. Postal services and public transportation were disrupted in Geneva.


Later studies found that the shortage of manpower – due to high mortality and the military draft - had a positive impact on wages in the manufacturing sector in a number of US locations hit hard by the flu. However, due to government restrictions such as travel bans across city and state boundaries, such wage increases remained limited to some location, with no equalisation occurring. Yet, the effects of wage increases as a consequence of the pandemic can be traced in a number of counties and cities up to the early 1930s when they start disappearing in the mayhem caused by the Great Depression.


In Sweden, the poverty rate among women increased significantly after 1918 which was associated with the death of young male breadwinners. It was one of the reasons cited by the government and Social Democratic legislators in parliament to make Sweden a paragon ‘welfare state’ in the 1920s and 1930s.


Long-term studies in the US show that the cohorts in utero during the 1918 pandemic suffered life-long consequences, with reduced educational achievements, higher rates of disability, and lower income. These effects can be evidenced up to the 1970s.


The US Mid-West experienced a wave of race riots in summer 1919, with further incidents extending into 1921, culminating in the Tulsa Massacre which killed about 250 African Americans and 50 whites. Sometimes, this outburst of violence, combined with the fear of Bolshevism, was attributed to the tense atmosphere prevailing in many cities after the flu experience. African Americans had suffered a disproportionately high mortality rate due to poor education and health and lower income. On the other hand, some of these cities harboured comparatively wealthy, commercially successful and self-confident black communities which drew the ire of and caused fear with white communities. The Ku Klux Klan was re-founded in 1920 and quickly had a multi-million membership. More recent studies, however, have dismissed too close a causal relationship between these two events though certain elements of influence cannot be excluded.


Impact on life insurance industry in the US


The US life insurance industry paid out claims of US$ 125 million (approximately 30 billion US$ today) related to the 1918 flu. That was 0.5 % of the US GDP. For many life insurers, profits for 1918 were wiped out and dividends had to be cut or cancelled. However, only a few insurance companies actually failed due to the 1918 pandemic, and the minimal life reserve regimes introduced in many states since the early 20th century stood the test.


The 1918 flu was a mixed blessing for life insurance companies: on the one hand, by primarily hitting young adults, it reduced the risk quality of portfolios. On the other hand, it emphasised the value proposition of life insurance. In 1919, some companies began to use the flu in their advertising. Others, however, refused to do so, arguing that it was not in the interest of the industry to attract customers only moved by the flu experience. The biggest life insurance company in the US – the New York-based Metropolitan Life – was among those rejecting influenza as an advertising topic.


Still, 1919 proved to be banner year for the life insurance industry in the US, with sales in Connecticut for example increasing by 79 % for ordinary life policies and 84 % for life assurance by fraternal unions and friendly societies. Premium rates increased moderately.


Beneficial effect of the flu on the life insurance proved to be transitory in the long term. This reflects a broader experience of early years of the US insurance industry. In 1917, the US Congress had passed the War Risk Insurance Act. It automatically enrolled every draftee in a government-managed insurance scheme that provided a 25-US$ per month pension to widows and surviving dependants in case of death. After the war, veterans had the option to continue the insurance scheme for a nominal fee. However, the vast majority dropped the scheme so that the government was forced to terminate the programme in the early 1920s.


Long-term effects of the Spanish Flu


In the end, the long-term effects of the flu were limited in terms of institutional and policy outcomes. There were no post-mortem assessments of the 1918-1920 experiences –neither by national nor local authorities - or major adjustments to public health management. Almost everywhere, the motto was “back to business as normal”. Influenza did become a reportable disease in the US only in 1925. Government health services were mostly built up only after the Second World War (in Europe) as part of a broader push for welfare institutions.


Internationally, the League of Nations founded in 1920 set up a Health Committee that was primarily focusing on fighting such diseases as malaria, yellow fever and leprosy. This committee was continued by the UNO after the League of Nations had become defunct, and it was transformed into the WHO. Only over time did this organisation gain a role as coordinator in international health and particularly in pandemic issues.


The Spanish Flu did not leave deep traces in public memory, in contrast to the First World War which continued to occupy the mind of both historians and laypeople. Only with the SARS epidemic of 2002 and the resurgent interest in the pandemic topic did the 1918 Spanish Flu regain some interest as a study object.

Other pandemics and COVID-19


The 18th century saw 4 or 5, the 19th century 5 and the 20th century 3 influenza-related pandemics. In the 21st century, the swine flu of 2009 was so far the only influenza-related pandemic. The 20th century pandemic viruses were all related to the 1918 H1N1 virus.

While very little is known about the etiology, genetic composition and mutations, mortality and morbidity rates, and proliferation and progression of pandemics in the 18th and 19th centuries, more data is available for the pandemics of the 20th century.

Source: Swiss Re, CDC

Except for the Spanish flu, all other influenza pandemics showed the normal pattern of mortality distribution, i.e., primarily impacted the very young and the elderly. While the elderly had a very low mortality in 1918-1920, it was 64 % for the Asian flu and 52 % for the Hong Kong flu. Also, outbreaks followed the normal pattern of pandemics.


As flu vaccination became available after the 1940s, mortality could be actively depressed with the 1957, 1968 and, to a lesser extent, the 2009 flus. Wide-spread vaccination in 1976 is credited with having prevented a swine flu outbreak in the US.


Neither the 1957 nor the 1968 flu pandemics led governments and health authorities to introduce drastic non-pharmaceutical measures as observed in 1918-20 or today. But there were significant behind-the-scene policy coordination efforts between national and international health authorities. While it is too early to understand all the elements of the current COVID-19 outbreak, including its medical patterns and consequences, the issue may arise why authorities remained largely quiescent in 1957/58 and 1968, but today react with measures going substantially beyond what were taken in 1918-1920 against the Spanish flu. It would seem that a response would have to include not only epidemiological, economic, social, and political considerations, but also considerations pertaining to the broader realms of ethics and concepts of understanding what human life and death means.

About the author


Dr. Rolf Tanner

Dr. Rolf Tanner is a trained historian and political scientist. He teaches undergraduate seminars at the university of Basel (political science) and lectures at the university of Zurich and a number of other Swiss establishments of higher education on historical, political science and risk management topics. Since 2002, he has been working with Swiss Re, first building up its political risk and sustainability management units, before becoming Global Head of Media Relations and Financial Reporting. He now leads Swiss Re's cultural sponsoring programme.





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