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.18It is also important to recognize that commercial interests may be inflating the perceived impact of influenza and other infectious “pandemics.”28 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.29(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.4 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.1(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.10 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.1113 Finally, I obtained monthly death statistics for 1994 through 1998 through the online DataFerrett utility.14 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.10

 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 sources16 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.”7(p61) In particular, influenza death rates dropped sharply around the end of World War II (1944–1945; Figure 1). 

Similarity Between Pandemic and Nonpandemic Influenza Seasons

With the notable exception of the 1918 pandemic, each influenza pandemic season was less lethal than the prior one, reflecting the overall seasonal trend in influenza deaths. Compared with nonpandemic seasons, the 1957–1958 and 1968–1969 pandemics do not stand out as exceptional outliers, nor were these pandemics visually discernable from nonpandemics in seasonal (Figure 1) or monthly (Figure 2) influenza mortality graphs. In fact, although nonpandemic influenza seasonal death rates never exceeded prior pandemic seasonal death rates, many nonpandemic seasons were more deadly than subsequent pandemics. For example, the 1941–1942, 1942–1943, 1943–1944, 1944–1945, 1945–1946, 1946–1947, and 1952–1953 nonpandemic seasons were all deadlier than the 1957–1958 pandemic season. Similarly, the 1959–1960 nonpandemic season was almost as deadly as the 1968–1969 pandemic season (Table 1). 

Pandemic years were difficult to distinguish from nonpandemic seasons, even in terms of peak monthly mortality. For example, in March of the 1975–1976 nonpandemic season (the season prior to the swine flu scare), the recorded influenza death rate was 22.1 per 100 000 population, nearly as high as the 1968–1969 pandemic peak of 23.3 per 100 000 in January 1969. Likewise, the influenza monthly mortality rate reached 21.9 per 100 000 in February 1960 (a nonpandemic year), surpassing the peak mortality rate of the 1957–1958 pandemic (18.8 per 100 000) 2 years earlier (Table 1).

DISCUSSION

The heightened concern over the threat of a future influenza pandemic largely rests on the assumption that the hallmark of pandemic influenza is excess mortality. However, this study indicates that the mortality impact of pandemic and nonpandemic seasons has been similar, with considerable overlap in both seasonal and peak monthly mortality rates.

Implications for Influenza Vaccines

Historical influenza mortality data contain many relevant implications for influenza vaccination campaigns. The overall decline in influenza-attributed mortality over the 20th century cannot be the result of influenza vaccination, because vaccination did not become available until the 1940s and was not widely used until the late 1980s.19 This rapid decline, which commenced around the end of World War II, points to the possibility that social changes led to a change in the ecology of influenza viruses.

I found that declining mortality rates occurred simultaneously with expanded influenza vaccine coverage since 1980, especially for the elderly (65 years and older).19 However, recent research suggests that vaccination is an unlikely explanation of mortality trends. A 2005 US National Institutes of Health study of over 30 influenza seasons “could not correlate increasing vaccination coverage after 1980 with declining mortality rates in any age group.”19(p265) Other research has reviewed available international studies of inactivated influenza vaccine effectiveness and efficacy. One study concluded that “evidence from systematic reviews shows that inactivated vaccines have little or no effect on the effects measured.”20(p915) Considered in light of the data presented here, these studies imply that other causes–such as an improvement in living conditions or naturally acquired immunity from similar strains of influenza virus–may have been partially responsible for the declining trends in recorded influenza

Naturally acquired immunity . Oh yah, herd immunity? It's real. This substantial decline preceded the widespread use of yearly vaccines- Think about that?Because it’s important. It’s clear that as living standards improved, mortality from infectious diseases reduced WITHOUT VACCINATION 

Hospital Surge Capacity

Beyond vaccines and drugs, increasing the health care infrastructure’s capacity is a major feature of many governments’ planning for a future pandemic of influenza. Those stressing the importance of erring on the side of caution have pointed to hospital surge capacity as a major concern. Emergency department overcrowding and ambulance redirect orders are situations that proper planning might help avoid, but it should be kept in mind that such needs are not unique to influenza.(virus)

Influenza, like many respiratory viruses, (including corona virus) circulates annually, and thus its timing is an important aspect to consider in decisions regarding hospital surge capacity. An influenza season with deaths and hospitalizations spread out evenly over 4 months will tax the medical infrastructure differently than if the same number of hospitalizations and deaths were to occur in a single month.Compared with annual or seasonal data, the monthly influenza mortality data I used in this study allowed more-detailed analysis of the actual timing of influenza seasons and their impact. In the monthly data from over 70 influenza seasons since the 1930–1931 season (the earliest time for which adjusted figures could be calculated), the peak monthly death rates in the 1957–1958 and 1968–1969 pandemic seasons were no higher than (and were sometimes exceeded by) those for severe nonpandemic seasons (Table 1). If these trends extend into the future, it follows that if the health care infrastructure has been capable of handling non-pandemic influenza, it will also be able to deal with pandemic influenza.

 There is lots more to read at the link, so take the time to read it all for yourself.I found it very enlightening and very relevant to our latest "pandemic"  

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