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Mortality rates of novel coronaviruses should not be directly compared with those of seasonal influenza (from JAMA)

[2020.05.24]

Seasonal influenza viruses and novel coronaviruses are often compared. The two are very similar as viral infections that infect the airways and cause death. 

However, the virulence of seasonal influenza, which is prevalent every winter and spring, is clearly different from that of the new coronavirus.

Spanish flu and new coronaviruses

The subject to be compared with the current COVID-19 pandemic is not seasonal influenza, nor the 2009 H1N1 flu, but the Spanish flu of 1918-1920, which was a pandemic about 100 years ago.

The number of people infected with the Spanish flu in Japan was reported to be 23.8 million (i.e., about half of the population at that time), with about 390,000 deaths and a fatality rate of 1.63%. It seems that both cytokine storms and bacterial infections were the cause of death in the Spanish flu (from Wikipedia).

 

Perspectives from the Journal of the American Medical Association (JAMA)

The paper presented here is from JAMA's VIEWPOINT (Perspective, Opinion).

The author challenges the U.S. Centers for Disease Control and Prevention, which makes policy by comparing the deaths and fatality rates of seasonal influenza with those of novel coronavirus infections.

 

Viewpoint
Assessment of Deaths From COVID-19 and From Seasonal Influenza

Jeremy Samuel Faust, MD, MS; Carlos del Rio, MD
JAMA Intern Med. 2020;180(8):1045-1046.

Published Online: May 14, 2020. doi:10.1001/jamainternmed.2020.2306

 

 

ーーーThe following is an easy-to-understand explanation with some quotes from the paper.ーーー
 "As of early May 2020, approximately 65 000 people in the US had died of coronavirus disease 2019 (COVID-19),1 the disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This number appears to be similar to the estimated number of seasonal influenza deaths reported annually by the Centers for Disease Control and Prevention (CDC) (https://www.cdc.gov/flu/about/burden/preliminary-in-season-estimates.htm). " 
"This apparent equivalence of deaths from COVID-19 and seasonal influenza does not match frontline clinical conditions, especially in some hot zones of the pandemic where ventilators have been in short supply and many hospitals have been stretched beyond their limits. The demand on hospital resources during the COVID-19 crisis has not occurred before in the US, even during the worst of influenza seasons. Yet public officials continue to draw comparisons between seasonal influenza and SARS-CoV-2 mortality, often in an attempt to minimize the effects of the unfolding pandemic. "

➡There are areas in the U.S. where COVID-19 has caused medical collapse. In contrast, even in years when seasonal flu pandemic caused many deaths, it did not cause medical collapse in the US.

 

"The root of such incorrect comparisons may be a knowledge gap regarding how seasonal influenza and COVID-19 data are publicly reported. The CDC, like many similar disease control agencies around the world, presents seasonal influenza morbidity and mortality not as raw counts but as calculated estimates based on submitted International Classification of Diseases codes.2 Between 2013-2014 and 2018-2019, the reported yearly estimated influenza deaths ranged from 23,000 to 61,000.3 "
"Over that same time period, however, the number of counted influenza deaths was between 3,448 and 15,620 yearly.4 On average, the CDC estimates of deaths attributed to influenza were nearly 6 times greater than its reported counted numbers. Conversely, COVID-19 fatalities are at present being counted and reported directly, not estimated. As a result, the more valid comparison would be to compare weekly counts of COVID-19 deaths to weekly counts of seasonal influenza deaths."

➡It means that the number of deaths from seasonal influenza is an estimate and not the actual number reported for each patient. Patients for whom influenza was not the direct cause of death may be included in the estimates, or the numbers extracted may be inappropriate and the calculation method may be wrong.

 

"During the week ending April 21, 2020, 15 455 COVID-19 counted deaths were reported in the US.5 The reported number of counted deaths from the previous week, ending April 14, was 14 478. By contrast, according to the CDC, counted deaths during the peak week of the influenza seasons from 2013-2014 to 2019-2020 ranged from 351 (2015-2016, week 11 of 2016) to 1626 (2017-2018, week 3 of 2018).6 The mean number of counted deaths during the peak week of influenza seasons from 2013-2020 was 752.4 (95% CI, 558.8-946.1).7  

These statistics on counted deaths suggest that the number of COVID-19 deaths for the week ending April 21 was 9.5-fold to 44.1-fold greater than the peak week of counted influenza deaths during the past 7 influenza seasons in the US, with a 20.5-fold mean increase (95% CI, 16.3-27.7).5,6"

➡Looking at the number of deaths per week, COVID-19 has 20 times more deaths than the numbers during the peak of the flu season. With these numbers, it is understandable that healthcare has collapsed.

 

"Case fatality rates are another topic of confusion. Comparisons of the case fatality rates of SARS-CoV-2 and influenza are premature. Estimates of case fatality rates for COVID-19 range from less than 1% in some nations to approximately 15% in others. This wide range reflects limitations in calculating case fatality rates.
These include failure to account for scarcity in testing (thereby falsely decreasing the denominator) and incomplete follow-up information for people who were critically ill but still alive when last assessed (thereby decreasing the numerator). Eventually, results from serologic studies will help to determine a more accurate denominator for the case fatality rate of SARS-CoV-2."

➡As of May 2020, the fatality rate should be higher in countries such as Japan that have suppressed the number of coronavirus PCR tests. At that time, the fatality rate in Japan was, on the contrary, low. I think the factors behind this will be analyzed in the future.

 

"At present, the Diamond Princess cruise ship outbreak is one of the few situations for which complete data are available. For this outbreak, the case fatality rate as of late April 2020 was 1.8% (13 deaths out of 712 cases); age adjusted to reflect the general population, the figure would have been closer to 0.5%.1,9   
A case fatality rate of 0.5% would still be 5 times the commonly cited case fatality rate of adult seasonal influenza.3,10"

➡The figure of 1.8% is almost the same as the fatality rate of the Spanish flu in Japan.

 

"Directly comparing data for 2 different diseases when mortality statistics are obtained by different methods provides inaccurate information. Moreover, the repeated failure of government officials and others in society to consider these statistical distinctions threatens public health. 
Government officials may rely on such comparisons, thus misinterpreting the CDC’s data, when they seek to reopen the economy and de-escalate mitigation strategies. Although officials may say that SARS-CoV-2 is “just another flu,” this is not true. 
In summary, our analysis suggests that comparisons between SARS-CoV-2 mortality and seasonal influenza mortality must be made using an apples-to-apples comparison, not an apples-to-oranges comparison. Doing so better demonstrates the true threat to public health from COVID-19."

 

written by the director of the Okino Medical Clinic, a Pulmonologist, M.D., Ph.D.

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