How can we apply lessons from the Spanish flu’s second wave to Covid-19?

Covid-19 infection rates are soaring in a variety of countries, several months on from the gruelling lockdowns that characterised the spring across the globe.

In the US, the average daily number of new confirmed infections has skyrocketed since mid-June – while in Spain, one of the countries the virus hit hardest in the early months of the pandemic, a big rise in cases prompted the UK to impose sudden travel restrictions on Saturday. Several countries previously acclaimed for managing the pandemic deftly – such as Australia and Vietnam – have seen alarming new coronavirus clusters.

The World Health Organisation argued on Wednesday that – despite journalists’ and politicians’ frequent use of it – the term “second wave” is inaccurate and that it would be preferable to describe Covid-19 as having “one big wave”, seeing as the virus never went away and does not follow seasonal variations.

“Covid-19 seems ready to come raring back into any population in the world the moment we let our guard down,” Joel Wertheim, an assistant professor of medicine at the University of California, San Diego, told FRANCE 24. “It’s important to distinguish between waves driven seasonally and the ebbing of Covid-19 due to public health measures.”

‘Lethal’

This puts it in stark juxtaposition to the previous pandemic to take the world by storm. The 1918-20 Spanish flu came in three waves, during which it killed at least 30 million people across the globe, with some historians putting the figure at 100 million – making it more deadly than the Great War that long overshadowed it in the collective memory.

This first wave of the pandemic in spring 1918 was highly contagious and put a gargantuan spanner in the works of both sides’ war efforts. Nevertheless, it was not especially virulent – official death rates were similar to those from the seasonal flu.

But in the autumn the virus re-emerged in a terrifying second wave, the most severe of the three. In the US – where the historical data on the Spanish flu is most complete – the excess mortality rate from September to December 1918 reached 266,000. “Let’s just say that the reconstructed virus continues to be lethal in lab animals,” John Barry, author of The Great Influenza, a study of the Spanish flu, told FRANCE 24.

The tendency of flu to evolve was likely responsible for this increased virulence, explained Erin Sorrell, an assistant professor of microbiology and immunology at Georgetown University: “The increase in lethality is assumed to be in part due to mutations accumulated by the virus in its initial first wave as influenza viruses are prone to point mutations called antigenic drift that allow them to evade existing immunity from previous infections,” she told FRANCE 24

In this respect, the coronavirus seems less menacing:  “This virus is much more stable,” Barry noted. “There is no hint anywhere in the world of it becoming more lethal, as happened in 1918.”

A ‘super spreader’ parade in Philadelphia

There was a range of different responses to the new strain of Spanish flu. In France, where it killed 240,000 people in all three waves collectively, during the second wave the government was still focused on the war effort, with the conflict in its endgame before the November 1918 Armistice. There were bans on some gatherings and a few public places were closed – but nothing on a similar scale to the Covid-19 lockdowns.

However, in the US – a combatant during the last year of the war, but which was spared the carnage seen on the Western Front – some authorities felt free to try and stem the disease’s spread, with several parts of the country shutting down schools, churches and restaurants.

“The initial wave was somewhat glossed over; the war was still very much ongoing, and doctors were focused on keeping soldiers healthy and on the battlefield,” Jim Harris, a historian of science at Ohio State University, told FRANCE 24. “But during the second wave when it became much more virulent, that’s when some policymakers felt forced to react.”

One notorious super-spreader event early in the second wave testifies to the benefits of social distancing measures. On September 28, 1918, more than 200,000 people attended the Philadelphia Liberty Loans Parade to promote the sale of US government war bonds – even though experts had told the city’s health commissioner that the event should not take place.

A historical lesson can be learned by comparing Philadelphia to St. Louis (which cancelled its parade along with other mass gatherings), according to the US Centers for Disease Control and Prevention: “The next month, more than 10,000 people in Philadelphia died from pandemic flu, while the death toll in Saint Louis did not rise above 700. This deadly example shows the benefit of cancelling mass gatherings and employing social distancing measures during pandemics.”

Experts say this contrast between Philadelphia and St. Louis is part of a bigger picture, in which public health measures clearly helped combat the Spanish flu. “We have learned that during the response to the 1918-19 pandemic (particularly in the US) those cities and states that enacted regulations for the use of face masks, banning large gatherings and closing schools fared better than those that did not,” Sorrell noted.

Young adults hit hard

The coronavirus has opened a generational divide over these kinds of measures – notably demonstrated by an episode this week in Brittany, where a cluster of cases among beachgoers in their twenties provoked a furious response from the French government’s top official in the region, who lambasted “irresponsible” young people “ignoring the danger”.

However, during the second wave of the Spanish flu, many young people were in the same position as the elderly today: the pandemic a century ago was especially lethal for previously healthy people aged 25 to 35. Its second wave affected age groups in a W-shaped curve – hitting infants, young adults and the elderly hardest. This was unusual because influenza – including the first wave of the Spanish flu – typically has a U-shaped curve: it is most dangerous for infants and the elderly, without being particularly virulent in young adults.

The question of why it affected this age group so brutally “has still not been answered”, Barry said. “There are only hypotheses,” he continued. “The most likely one is that young people have stronger immune systems, which overreacted, creating cytokine storms in the lungs” – in which the body’s overly active defences cause even more inflammation.

Even amid this bewildering phenomenon, many people from all age groups tired of taking precautions to avoid contagion as the months went on: during both the coronavirus pandemic and the second wave of the Spanish flu, “People think there comes a moment when it’s time for all this to be over”, Naomi Rogers, a professor of the history of medicine at Yale University, told FRANCE 24.

Despite some hubristic behaviour during the current crisis, the huge advances in science and technology since the time of the Spanish flu – when the nature of viruses remained a mystery – are a genuine source of hope, Sorrell added: “We have, on a global scale, scientific skill and expertise, technology, resources and methods for information sharing.”

However, she continued, there remains a crucial task in the fight against the coronavirus – highlighted by the catastrophic results in places like Philadelphia during the second wave of the Spanish flu, where officials refused to heed warnings about the need for social distancing. “Our challenge today,” said Sorrell, “is in disseminating the correct information to the public about the pandemic, giving credit and a voice to our scientists to dispel misinformation and encouraging our national leaders to prioritise public health preparedness and response.”