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What we don’t know about pandemic influenza

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BMJ Blogs: Dr Kieran Walsh

What we don’t know about pandemic influenza

Pandemics of influenza have been occurring for about five hundred years. (1) As a result, we can be confident that we know the symptoms and signs of influenza. These include cough, fever, sore throat, nasal congestion, muscle pains, headache and fatigue. But this is not an achievement for modern medicine to be especially proud of, as we have known these clinical features for about 500 years. Indeed, we could speculate that physicians of the sixteenth century knew more about the clinical features than we do. Morens et al have outlined what physicians knew about the clinical features of the disease in their paper on eyewitness accounts of the 1510 influenza pandemic in Europe. (2)

Physicians described the disease as a “precipitous illness…with coughing and a high fever”. Another described the symptom of anorexia leading to “extreme distaste for bread and wine”. A final description outlines “a great deal of clearing of the throat that is viscous, slow, not a little thin, and quite foamy. Following that there being sputum, coughing, and difficulty in breathing may return for several [days]…weakness of the body…and aversion to food…restlessness, weakness, wakefulness caused by a strong cough all press them…[and] from others a great deal of sweat flows.” These are vivid descriptions which are often missing from modern case reports of the disease (such case reports are often dominated by radiological and laboratory findings to the virtual exclusion of clinical findings).  

But 500 years later, there is still a lot that we don’t know about influenza. In a subsequent paper, Morens and Taubenberger outlined just some of the just some of the things that we don’t know. We don’t know how and why influenza pandemics emerge or why influenza pandemics differ in severity. We don’t know why influenza pandemics recur, or why they recur in differing patterns, or even why some pandemic viruses disappear. We often feel that we are making progress with regards to our knowledge of influenza, only for a new pandemic to occur that doesn’t seem to follow the rules laid out by previous pandemics.  

This all makes is exceptionally difficult to predict how pandemic influenza might behave in the future or what we should do to prevent such pandemics. So what should public health authorities do? In some ways such authorities are in a no-win situation. If they don’t adequately warn the public of risks, then they will be blamed. If they overreact and advise of dangers that subsequently don’t materialize, then they will be blamed also. The answer must lie in more and better basic science, epidemiological and clinical research. But part of the answer must also lie in a resistance to trust in “accepted truths” about a disease that we really don’t know a great deal about at all.  




1. Morens DM, Taubenberger JK. Pandemic influenza: certain uncertainties. Rev Med Virol. 2011 Sep; 21(5): 262–284.

2. Morens DMNorth MTaubenberger JK. Eyewitness accounts of the 1510 influenza pandemic in Europe. Lancet. 2010 Dec 4;376(9756):1894-5.

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