(CN) — The death toll of the Covid-19 pandemic is often compared to that of seasonal influenza, but conditions on the front lines suggest casualties of Covid-19 are likely much higher, according to a new study.
As of Thursday morning, nearly 85,000 people in the United States have died from the Covid-19 disease, caused by the severe acute respiratory syndrome SARS-CoV-2. While many equate this dreadful number to the estimated number of seasonal influenza deaths reported annually by the U.S. Centers for Disease Control and Prevention, scientists believe doing so belies conditions on the front lines, especially in some hot zones of the pandemic where many hospitals ran low on ventilators and were pushed past their limits.
This is the first time in U.S. history that we’ve seen this demand for hospital resources, with conditions that far exceeded even the worst flu seasons. Despite this, however, public officials continue to draw comparisons between seasonal influenza and Covid-19 mortality rates, most often to mitigate the effects of the current pandemic. The authors of this study, published Thursday in the Journal of the American Medical Association, note that this issue of misinformation could be due to a knowledge gap regarding how seasonal influenza and Covid-19 data are publicly reported.
The CDC presents seasonal influenza morbidity and mortality not as raw numbers, but as calculated estimates based on submitted International Classification of Diseases codes. Between the years 2013-2014 and 2018-2019, the reported yearly estimated influenza deaths ranged from 23,000 to 61,000, but over that same period the number of counted influenza deaths was between 3,448 and 15,620 annually. So on average, the CDC estimates of deaths attributed to influenza were nearly six times greater than its reported counted numbers.
Conversely, Covid-19 fatalities are presently being counted and reported directly, not estimated, leading scientists to believe a more accurate comparison would be of weekly counts of Covid-19 deaths and weekly counts of seasonal influenza deaths. For example, in the week ending April 21, 2020, 15,455 Covid-19 deaths were counted in the United States and the reported number of counted deaths from the previous week, ending April 14, was 14,478.
In stark contrast, according to the CDC, counted deaths during the peak week of the influenza seasons from the time period 2013-2014 to 2019-2020 ranged from 351 (2015-2016, week 11 of 2016) to 1,626 (2017-2018, week 3 of 2018).
These shocking statistics on counted deaths suggest the number of Covid-19 deaths for the week ending April 21 was 9 to 44 times greater than the peak week of counted influenza deaths spanning over the past seven influenza seasons in the U.S.
The CDC also publishes provisional counts of Covid-19 deaths, acknowledging that its reporting lags behind other public data sources. For the week ending April 11, 2020, data indicate the number of provisionally reported Covid-19 deaths was 14.4-fold greater than influenza deaths during the apparent peak week of the current flu season (week ending Feb. 29, 2020), consistent with the ranges based on CDC statistics. It’s suspected that as the CDC continues to revise its Covid-19 counts to account for delays in reporting, the ratio of counted Covid-19 deaths to influenza deaths will increase.
These ratios are more clinically consistent with frontline conditions than those that would compare Covid-19 fatality counts and estimated seasonal influenza deaths. Based on the reported figure of 60,000 Covid-19 deaths at the end of April 2020, this ratio suggests only a 1.0-fold to 2.6-fold difference from the CDC-estimated seasonal influenza deaths calculated during the previous seven full seasons. From this analysis, scientists infer that the current number of Covid-19 counted deaths substantially understates the actual number of deaths, for several reasons.
Deaths from Covid-19 could be undercounted due to the ongoing limitation of tests or false-negative test results, which occur when patients present late in the course of illness and their upper respiratory tract samples are less likely to yield positive results. Furthermore, the counts may be less reliable because adult influenza deaths and adult Covid-19 deaths are not reportable to public health authorities, leaving epidemiologists to rely on surveillance mechanisms that attempt to account for potential underreporting.
Moreover, some cities, including New York, are now reporting cases of both probable and confirmed Covid-19 deaths, resulting in revised mortality figures that sit on the fence between counting and estimating. It’s also possible that some of the deaths labeled as Covid-19 deaths could have been caused by something else. For example, in areas where there is high-level community spread like New York, if a patient is brought into an emergency room in cardiac arrest and has tested positive for Covid-19 and then dies, that would be considered a Covid-19 death in local death counts.
The scientists note a more complete picture that focuses on excess mortality, including both direct and indirect Covid-19 related deaths, will be much more helpful. That analysis will be most accurate if it also includes the possibility of excess deaths caused by deferred care during the peak of the pandemic and the lack of capacity for care of patients without Covid-19 at overwhelmed hospitals.
Additionally, case fatality rates are confusing as comparisons between Covid-19 and influenza are premature. Some estimates of case fatality rates for Covid-19 can range from less than 1% in some nations but approximately 15% in others, reflecting the limitations of calculating this right now. These discrepancies include failure to account for scarcity in testing as well as incomplete follow-up information for people who were critically ill, but still alive when last assessed, but scientists add that eventually serologic studies will help determine a more accurate rate.
To date, the Diamond Princess cruise ship outbreak is one of the rare situations for which complete data is available. In this outbreak, the case fatality rate as of late April 2020 was 1.8%, with 13 deaths out of 712 cases. But adjusting age to reflect the general population, the figure would have been closer to 0.5%, still five times the commonly cited case fatality rate of adult seasonal influenza.
The authors emphasize that comparing data from different diseases when mortality statistics are obtained by different methods results in inaccurate information, and the repeated failure of government officials to consider these statistical distinctions threatens public health. Public officials may make such comparisons to reopen the economy and de-escalate mitigation strategies, but doing so misinterprets the CDC’s data.
“Our analysis suggests that comparisons between SARS-CoV-2mortalityand 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,” the authors said in conclusion.