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During the recent severe 2019–2020 influenza season, vaccination is. . . estimated to have prevented 7.5 million illnesses, 105,000 flu hospitalizations, and 6,300 deaths (CDC, 2020).
Influenza is one of the deadliest viruses in the world, yet we take for granted that we are protected from its ill effects. We are deathly afraid of other viral infections, any of which kill only a fraction of the people that die each year from influenza. Yet many of us skip our annual flu shots, giving various excuses for forgoing the vaccine. This is despite the fact that the impact of influenza is enormous—estimated to be about 1 billion cases worldwide with death in nearly half a million people.
The 2017–2018 influenza season was severe, with high levels of outpatient clinic and emergency department (ED) visits for influenza-like illness (ILI), high influenza-related hospitalization rates, and elevated and geographically widespread influenza activity for an extended period. In 2017 the Centers for Disease and Prevention (CDC) began using new methodology to classify seasonal severity and applied the methodology to the 2003–2004 through 2016–2017 seasons. The 2017–2018 season was the first season to be classified as high severity across all age groups (CDC, 2019q).
The 2018–2019 influenza season was of moderate severity and differed from recent seasons in that there were two waves of influenza A activity of similar magnitude. It was also longer than recent seasons with activity at or above baseline for 21 consecutive weeks. Overall, hospitalization rates were below those of the previous season, but rates for children under 17 years of age were similar to the previous year (Xu et al., 2019).
Influenza is a clever virus—it shifts, drifts, and adapts, every so often mutating into a virus to which humans have little or no immunity. When this happens, a pandemic can occur, as in 1918 when a devastating influenza pandemic killed tens of millions of people throughout the world. Some of us lost grandparents, aunts, or uncles to the 1918 pandemic. All influenza A pandemics since that time, and almost all cases of influenza A worldwide, have been caused by descendants of the 1918 H1N1 virus (Taubenberger & Morens, 2006).
One hundred years ago the 1918 influenza pandemic devastated entire communities and took an estimated 675,000 American lives. It was the most severe pandemic in recent history, sweeping the globe quickly and killing more than 50 million people. Source: CDC.
Respiratory tract infections, such as those caused by influenza, are the most common type of infection worldwide, representing a source of significant morbidity and a considerable economic burden. So, it is not a surprise that, in late 2019, a respiratory virus with symptoms similar to those caused by influenza (SARS-CoV-2, or COVID-19) began to spread globally. Within a short period of time, this highly infectious virus spread to every country in the world. Like other respiratory viruses, SARS-CoV-2 spreads easily via droplets, via direct and indirect contact and via tiny aerosol droplets that can stay suspending in the air for more than an hour.
The emergence of a global pandemic 100 years after the 1918–1919 influenza "mother of all pandemics" has led us to look back to analyze what worked and what didn't work in 1918. What started as a mild outbreak in the spring of 1918 was followed by a much more serious outbreak in the fall. Scientists and politicians initially downplayed the pandemic, believing it was caused by a bacterium rather than a virus—perhaps cholera or bubonic plague. With no vaccine and few analytic tools, public health practices such as masks, social distancing, refraining from spitting in the street, and covering your mouth when sneezing became important tools to slow the spread of the virus.
Curiously, many of the political and personal issues we face today also occurred in 1918. Early on, public health officials, including President Woodrow Wilson, argued that the flu outbreak was caused by "ordinary" influenza and stated that the public need not worry so long as simple precautions were followed. There was no general lockdown, although many cities closed saloons, theatres, and places of public gathering (Soucheray, 2020, April 10) and, in the end the areas of the country that enforced strict public health measures fared better than areas that did not. In January 1919, President Wilson and several members of his staff were felled by a severe case of the flu. The White House physician downplayed the President's illness, arguing that his symptoms were due to overwork and rainy weather (Solly, 2020, October 2).
Resistance to mask wearing, quarantine orders, and bans on public gatherings was not uncommon in 1918 (many people poked holes in their masks to allow smoking). Despite this, fear was pervasive and there was widespread absenteeism from work, whether out of fear or because workers were caring for sick people (Soucheray, 2020 April 10).
Even if you are not familiar with the 1918 pandemic, you may be aware of the 2009 H1N1 pandemic—the first global influenza pandemic in more than forty years. It was caused by the emergence of a novel* H1N1 influenza strain that reminded us just how serious an influenza pandemic can be. By the time the World Health Organization (WHO) declared the pandemic officially over in August 2010, the CDC estimated that 43 to 89 million people in the United States had become infected and more than 12,000 had died. It is estimated that worldwide between 151,700 and 575,400 people died from 2009 H1N1 virus infection during the first year the virus circulated (CDC, 2018d).
*Novel: New (novel) influenza viruses are different from those currently circulating. This can include highly pathogenic influenza A viruses (H1N1, H5N1, H7N3, and H7N9).
Influenza experts believe that another influenza pandemic will occur—likely caused by an influenza subtype to which there is little or no pre-existing immunity in the human population. Even though the H1N1 pandemic of 2009 is officially over, the H1N1 virus continues to circulate as a seasonal virus and is expected to do so for several years. Fortunately, most (although not all) countries have developed influenza vaccines that protect against the H1N1 virus.