The Spanish flu, however, was different. For reasons that are not entirely clear, the Spanish flu struck in two waves. The first wave, in the spring of 1918, induced typical flu-like illness with generally mild outcomes, except for the immunocompromised. The second wave was unusual for two reasons. First, it began in the late summer of 1918, rather than the typical winter pattern seen in North America. Second, it was much more deadly, inducing what has been termed a cytokine storm. This immunological avalanche produced more severe disease in the immunopotent young, healthy populations—resulting in its unprecedented mortality in this cohort. In fact, upward of 99% of all Spanish flu deaths were in people younger than 65.
In the end, the pandemic left a broad swath of destruction in its wake. It is estimated that 500 million people—one-third of the world’s population at the time—were infected. The mortality rate was 10% to 20%, resulting in 50 million to 100 million deaths. Put another way, the Spanish flu killed 5% of humanity.
It did so rapidly. Nearly 1 million people died per week in the first 25 weeks of the second wave. To put it in perspective, it took HIV 25 years to reach that number. Thus, historians have termed the Spanish flu “the greatest medical holocaust in history.”
And then as quickly as it commenced, it abated. For example, in Philadelphia, there were about 5,000 flu deaths in one week in October 1918, yet a month later, the virus had nearly disappeared from the city. It’s not clear why this happened, but prevailing theories postulate that either the medical community got better at managing its mortal complications (e.g., bacterial pneumonia), or the bug itself mutated to a less virulent strain.
Is the Swine Flu our Spanish Flu?
On June 11, 2009, the World Health Organization (WHO) declared that the current H1N1 flu virus had reached pandemic status. This novel H1N1 serotype appears to be a direct descendent of the Spanish H1N1 subtype, but the new strain also combines genetic material culled from swine and birds reassorted in a manner that results in limited innate human defenses. And like the Spanish variant, it appears this new strain is hitting earlier in the year than usual and disproportionately affecting the young, with about two-thirds of U.S. deaths coming in the 25- to 64-year-old demographic.
So can we expect hundreds of millions of deaths from swine flu? Probably not. The WHO has been cautious to note that the upgrade to pandemic status was based on the rapidity and ease of spread, not the lethality of the virus. Furthermore, the Centers for Disease Control and Prevention (CDC)—which publishes a wonderful weekly update called FluView (www.cdc.gov/flu/weekly/)—notes that while the number of doctor’s visits for influenza-like illnesses through mid-August is unusually high, the rates of hospitalizations and proportion of deaths attributed to pneumonia and influenza are low and within normal limits for this time of year. Further, the virus continues in its original form, meaning it has not mutated, become more resistant to antiviral drugs, or been altered from the viruses selected for the 2009 vaccine.
So while we certainly must brace for the worst, I feel comfortable in the answer I provided my family member. I also am confident that Grey won’t be quarantined or left to roam the barren Earth anytime soon. TH
Dr. Glasheen is associate professor of medicine at the University of Colorado Denver, where he serves as director of the Hospital Medicine Program and the Hospitalist Training Program, and as associate program director of the Internal Medicine Residency Program.