Early Evidence of Virus Behind 1918 Flu Pandemic

1918 Influenza Scrapbook, The College of Physicians of PhiladelphiaThe so-called Spanish influenza pandemic of 1918 was one of the worst natural disasters in history. Estimates of total death counts vary, but it is commonly stated that the virus infected about one-third of the world’s population and killed about 50 million – possibly as many as 100 million. Researchers have long been interested in learning more about the virus and what made it so deadly, and genetic analysis has been a large part of that effort. In 2005 the full genome sequence of the virus was published, and research has continued from that point.

The virus behind the 1918 pandemic was an H1N1 strain; in fact, it was the only H1N1 strain to cause a pandemic in the 20th century. (Pandemics that began in China in 1956 and Hong Kong in 1968 were caused by H2N2 and H3N2 strains, respectively.) It was unusually severe, and in an unexpected result for an influenza virus, tended to kill healthy young adults rather than the typical flu victims – the very old and the very young. This contributed to the initial fear when novel H1N1 appeared in 2009, particularly since the number of deaths per age group early in the outbreak skewed heavily toward young adults.

Although the 2009 H1N1 pandemic fortunately did not become a 1918-scale disaster, the 1918 virus is still of great interest to researchers and may provide clues to help prevent or mitigate future outbreaks. One researcher, Jeffrey Taubenberger, MD, has been studying the 1918 H1N1 virus since the 1990s, and was the lead researcher in the team that determined and published the complete genome sequence. Now, Taubenberger and colleagues have analyzed autopsies of military patients who died before and during the 1918 pandemic, providing new information about when the virus began to gain a foothold in the United States.

As with the research that allowed them to determine the virus’s full genome sequence, Taubenberger and his colleagues used materials from the National Tissue Repository of the Armed Forces Institute of Pathology. In this case, they analyzed all of the autopsy records that included lung-tissue blocks preserved using formalin and paraffin. All of the 68 soldiers whose cases were examined had been stationed in Army training camps; nine of them had died between May 11 and August 8, when little flu activity had been reported in the country and the pandemic had not yet been identified in the United States. The results of the researchers’ analysis suggest that the virus was  circulating for four months – or longer – in the United States before the pandemic was detected in the fall of 1918. These findings at last provide evidence to support the commonly held view that a first wave of the Spanish influenza occurred in the United States in spring 1918.

This finding, the authors note, is expected considering the massive outbreak in the country in the fall of 1918. They speculate that the “lack of detectible disease and mortality” in the months before the pandemic meets the expected behavior of a virus brought into the United States from abroad and needing time to spread. The origin of the virus, however, is still unknown.

At this point, the largest mystery that remains is why the 1918 virus killed so many people, and in particular so many young and healthy individuals.

The History of Vaccines features a growing collection of resources about influenza. See our article on Influenza Pandemics for more information about the 1918 flu and other pandemics of the 20th and 21st centuries, as well as our video segment with Maurice Hilleman discussing the 1957 Asian flu pandemic, and assorted photographs from the 1918 epidemic.


Sources and Further Reading

Epatko L. 1918 Spanish Flu Offers Clues About Pandemic Viruses. PBS Online NewsHour. November 1, 2005. Available at http://www.pbs.org/newshour/indepth_coverage/health/birdflu/1918flu.html.

Taubenberger JK, Morens DM. 1918 influenza: the mother of all pandemics. Emerg Infect Dis [serial on the Internet]. 2006 Jan . Available at http://wwwnc.cdc.gov/eid/content/12/1/pdfs/v12-n1.pdf

Zong-Mei Sheng et al. Autopsy series of 68 cases dying before and during the 1918 influenza pandemic peak. Proc Natl Acad Sci. 2011. Available at http://www.pnas.org/cgi/doi/10.1073/pnas.1111179108