Wednesday, May 27, 2020

Trends in Historical Influenza Mortality: Pandemic vs Non Pandemic Seasons.

You will find an interesting read awaiting you. 
 While this study relates to influenza virus, it can equally apply to a corona virus in a pandemic vs non pandemic situation. It's a valid comparison. You see, I do read the science.Published at the US National Library of Medicine National Institutes of Health

Link to the work below

We're going to begin at the end. Which will surely entice you into reading the entire research paper

Explaining the Gap Between Evidence and Fear

The notion that pandemic influenza’s fundamental property is excess mortality is difficult to reconcile with the recorded influenza death data over the past century. There are many possible explanations, one of which may be the tendency to generalize the exception–the 1918–1919 pandemic. In 1918, doctors lacked intensive care units, respirators, antiviral agents, and antibiotics, an important fact in light of historical evidence of interactions between influenza and secondary bacterial respiratory pathogens (e.g., Haemophilus influenzae) as a significant cause of death during the pandemic.
It is also important to recognize that commercial interests may be inflating the perceived impact of influenza and other infectious “pandemics. There is a clear need for more evidence-based accounts of influenza in the context of historical epidemiology and current social and medical advances.
Another possible explanation for the false assumption that pandemics are necessarily more deadly than nonpandemics may lie in an inaccurate understanding–and inconsistent use–of the word “pandemic.”
Influenza virus circulates the globe on an annual basis, but is usually not labeled a pandemic until the strain of virus in wide circulation is substantially novel (i.e., it carries a different hemagglutinin or neuraminidase protein than the strains already in circulation).
Do you understand that? It is called a "pandemic" because it's substantially different virus. NOT BECAUSE IT IS NECESSARILY MORE DEADLY- Get it?
The 1977–1978 season illustrates this confusion, for although the season is not generally recognized as a pandemic, some have called it a pandemic because of the reemergence of the H1N1 virus.(p2535) Thus, there is no a priori connection between influenza pandemics and exceptional mortality.
Whatever the reasons for the misconceptions, should the trends observed over the 20th century continue to hold in the 21st, the next influenza pandemic may be far from a catastrophic event.

Now that you've read the end- let's walk the path that takes us to our destination. Or in this case let's read how this conclusion came to be.

Abstract

Objectives. I sought to describe trends in historical influenza mortality data in the United States since 1900 and compare pandemic with nonpandemic influenza seasons.
Methods. I compiled a database of monthly influenza-classed death rates from official US mortality tables for the years 1900 to 2004 (1905–1909 excluded), from which I calculated adjusted influenza season (July 1–June 30) mortality rates.
Results. An overall and substantial decline in influenza-classed mortality was observed during the 20th century, from an average seasonal rate of 10.2 deaths per 100 000 population in the 1940s to 0.56 per 100 000 by the 1990s. The 1918–1919 pandemic stands out as an exceptional outlier. The 1957–1958 and 1968–1969 influenza pandemic seasons, by contrast, displayed substantial overlap in both degree of mortality and timing compared with nonpandemic seasons.
Conclusions. The considerable similarity in mortality seen in pandemic and non-pandemic influenza seasons challenges common beliefs about the severity of pandemic influenza. The historical decline in influenza-classed mortality rates suggests that public health and ecological factors may play a role in influenza mortality risk. Nevertheless, the actual number of influenza-attributable deaths remains in doubt.
 Despite the widespread concern over a future influenza pandemic, there has been little research on the more than 100 years of recorded influenza death data in the United States–a period that includes both pandemic and nonpandemic seasons. I present an analysis of these data to describe trends in influenza mortality and, in particular, to compare pandemic and nonpandemic influenza seasons in ways that may inform present planning for the prevention and control of influenza.

METHODS

Mortality Statistics and Influenza - get this information at link

Definitions of Influenza Seasons

In the United States, influenza is a seasonal illness, and virus circulation peaks at unpredictable times. Elevated mortality thus can occur across calendar years. For those years for which full monthly data were obtainable, I have defined an influenza season as the 12-month period between July 1 and June 30.
Subsequently, I categorized influenza seasons as either pandemic or nonpandemic. Pandemic influenza seasons are those in which “a new influenza A virus appears or ‘emerges’ in the human population, causes serious illness, and then spreads easily from person to person worldwide,” as defined by the CDC.(p1) All other seasons are “nonpandemic.”
additional information at link

Influenza Mortality Data

Monthly total US influenza and all-cause death figures were obtained for the years 1900 through 1904 and 1910 through 2004. For the years 1900 through 1904 and 1910 through 1936, monthly death figures were obtained through the annual Mortality Statistics reports published by the Bureau of the Census. I obtained additional figures for the years 1937 through 1993 and 1999 through 2004 from Vital Statistics of the United States or other mortality reports maintained or produced by the CDC’s National Center for Health Statistics. Finally, I obtained monthly death statistics for 1994 through 1998 through the online DataFerrett utility. For reasons unknown, the Bureau of the Census did not publish statistics on the causes of death by month for 1905 through 1909, but did both before and after this period. For these years, only annual (January–December) death figures could be located.
 additional information at link 

Comparability Between International Classification of Diseases Revisions

There were 10 different revisions of the ICD in the period under review, from ICD-1 in 1900 to the current ICD-10, which was first applied to US national mortality data in 1999. During this time, the classification code for influenza was changed several times (see the table available as a supplement to the online version of this article at http://www.ajph.org). I obtained comparability ratios for influenza through published National Center for Health Statistics sources to adjust the data classified under revisions ICD-4 through ICD-9 (years 1930–1998). I adjusted these data to the current ICD-10 scheme. Comparability ratios were not available for adjustment of data for the years classified under the ICD-1, ICD-2, and ICD-3 revisions (years 1900–1929).

Viral Circulation Data

Viral circulation data on influenza as well as other viruses such as respiratory syncytial virus and rhinovirus may be helpful in an analysis of influenza’s impact on mortality, because these viruses often co-circulate with influenza. The CDC maintains such historical viral circulation data through programs such as the National Respiratory and Enteric Virus Surveillance System.

RESULTS

Overall Decline in Death Rate

Influenza death rates in the United States substantially declined across the 20th century, in line with the simultaneous decline in the mortality burden from most infectious diseases, often referred to as the “epidemiological transition.”(p61) In particular, influenza death rates dropped sharply around the end of World War II (1944–1945; Figure 1).