COVID-19: Archive - June 2020

New information about COVID-19 is constantly emerging. This page has not been updated since June 2020.

SARS-CoV-2

CVID-19: Assessing Infection Severity

1. HOW CAN THE SEVERITY OF COVID-19 BE CALCULATED?

COVID-19 (coronavirus disease 2019) is caused by the SARS-CoV-2 virus, the newest strain among seven coronaviruses known to infect humans.1 Although more than 99% of people infected with SARS-CoV-2 fully recover, some cases involve severe complications and could be fatal.2 The severity of COVID-19 can be measured by calculating a case-fatality rate (CFR): dividing the number of people who died from the infection by the total number of people who were infected.3 In the context of COVID-19 epidemiological studies, the CFR is sometimes expressed as an infection-fatality rate (IFR).4

2. HOW CAN THE TOTAL NUMBER OF SARS-COV-2 INFECTIONS BE DETERMINED?

Public health departments and Centers for Disease Control and Prevention (CDC) track and report SARS-CoV-2 infections detected from people seeking medical care (i.e., those who have a nose or throat swab test that is positive for genetic material from the virus).5 However, the majority of infections occur in people who don’t seek medical care and are therefore not reported. Per CDC, “Most people have mild illness and can recover at home without medical care.”6

Antibody surveillance studies, however, are able to capture the proportion of asymptomatic and mild infections that occur from unreported cases (people who don’t seek medical care) by testing for SARS-CoV-2 antibodies in blood (specific proteins produced by one part of the immune system in response to previous infection).5,7 These types of antibody tests more comprehensively capture the total number of SARS-CoV-2 infections (both reported and unreported cases) in a population, increase the denominator in the CFR equation, and decrease the reported case-fatality rate to more closely match the true rate.8 See Figure 1.

3. HOW ARE THE NUMBER OF COVID-19 DEATHS DETERMINED?

Until the peak of the pandemic, all deaths with positive laboratory confirmation of SARS-CoV-2 infection were counted as COVID-19 related deaths. However, on April 14, 2020, the CDC adjusted the criteria for counting a COVID-19 death to no longer require a positive laboratory test.9 This adjustment can increase the numerator in the CFR equation and increase the CFR.

4. HAVE THERE BEEN ANY CFR ESTIMATES BASED ON ANTIBODY STUDIES?

Yes, several public health departments and research institutions have conducted antibody surveillance studies to determine the prevalence of SARS-CoV-2 in a sample of the population and used that data to estimate the total number of infections (both reported and unreported).10-18 See Table 1. The number of deaths is divided by the number of infections to calculate the case-fatality rate. The average CFR of the antibody studies shown on Table 1 is 0.26%.

5. WERE INITIAL ESTIMATES OF SARS-COV-2 SEVERITY BASED ON ANTIBODY STUDIES?

No. On March 3, 2020, the World Health Organization (WHO) wrote that globally “about 3.4% of reported COVID-19 cases have died”19—a figure that did not include unreported cases. On March 16, a report from Imperial College London stated, “the public health threat [that COVID-19] represents is the most serious seen in a respiratory virus since the 1918 H1N1 influenza pandemic” and that SARS-CoV-2 is “a virus with comparable lethality to H1N1 influenza in 1918.”20 Neither the latter report nor similar CDC modeling predictions publicized on March 13 were based on antibody testing.21

6. HAVE THERE BEEN ANY ESTIMATES OF THE SARS-COV-2 CFR SINCE THE ANNOUNCEMENT OF THE RESULTS OF ANTIBODY STUDIES?

Yes. In May 2020, the CDC estimated that the overall CFR of SARS-CoV-2 based on symptomatic cases is 0.4%. The CDC also estimated that 35% of SARS-CoV-2 infections are asymptomatic, resulting in an overall CFR of 0.26% (0.4% times 65%), ranging from 0.03% in people younger than 50 to 0.8% in people 65 and older.2

7. WHAT IS THE SEVERITY OF SARS-COV-2 RESPIRATORY ILLNESS COMPARED TO FLU SEASONS?

Relative to CFRs that are based on both reported and unreported cases, the CFR of SARS-CoV-2 is comparable to that of respiratory illness (both flu and pneumonia) during seasons of typical or pandemic flu, and SARS-CoV-2 is significantly less severe than the 1918 flu pandemic.22-24 Table 2 shows the CFR of respiratory illness during several flu seasons and pandemics.

 

As Fauci et al. noted in the New England Journal of Medicine, a case-fatality rate of SARS-CoV-2 “considerably less than 1%…suggests that the overall clinical consequences of COVID-19 may ultimately be more akin to those of a severe seasonal influenza (which has a case fatality rate of approximately 0.1%) or a pandemic influenza (similar to those in 1957 and 1968).”25

Note: CFR calculations of both SARS-CoV-2 and influenza may be affected by several factors, including the accuracy of disease diagnosis, the accuracy of antibody testing, the time it takes for antibodies to develop after infection, the time span between infection and reporting of death, treatment protocols, and the characteristics of study populations, such as geography and age distribution.

References

  1. Centers for Disease Control and Prevention. Washington, D.C.: U.S. Department of Health and Human Services. Human coronavirus types; [cited 2020 May 31]. https://www.cdc.gov/coronavirus/types.html.
  2. Centers for Disease Control and Prevention. Washington, D.C.: U.S. Department of Health and Human Services. COVID-19 pandemic planning scenarios; [cited 2020 May 23]. https://www.cdc.gov/coronavirus/2019-ncov/hcp/planning-scenarios.html.
  3. Centers for Disease Control and Prevention. Washington, D.C.: U.S. Department of Health and Human Services. Principles of epidemiology in public health practice, third edition: an introduction to applied epidemiology and biostatistics, lesson 3—measures of risk; [cited 2020 May 6]. https://www.cdc.gov/csels/dsepd/ss1978/lesson3/section3.html.
  4. Oke J, Heneghan C. Global COVID-19 case fatality rates. Oxford (UK): Centre for Evidence-Based Medicine; 2020 Mar 17 [updated 2020 May 19; cited 2020 May 19]. https://www.cebm.net/covid-19/global-covid-19-case-fatality-rates/.
  5. Centers for Disease Control and Prevention. Washington, D.C.: U.S. Department of Health and Human Services. Coronavirus disease 2019 (COVID-19): COVID-19 serology surveillance strategy; [cited 2020 May 5]. https://www.cdc.gov/coronavirus/2019-ncov/covid-data/serology-surveillance/index.html.
  6. Centers for Disease Control and Prevention. Washington, D.C.: U.S. Department of Health and Human Services. Coronavirus disease 2019 (COVID-19): test for current infection; [cited 2020 May 5]. https://www.cdc.gov/coronavirus/2019-ncov/testing/diagnostic-testing.html.
  7. Centers for Disease Control and Prevention. Washington, D.C.: U.S. Department of Health and Human Services. Coronavirus disease 2019 (COVID-19): serology testing for COVID-19; [cited 2020 May 5]. https://www.cdc.gov/coronavirus/2019-ncov/lab/serology-testing.html.
  8. Consortium for the Standardization of Influenza Seroepidemiology (CONSISE). Oxford (UK): Global Health Network. Cross-sectional seroprevalence study of novel coronavirus (nCoV) infection prior and post epidemic periods; 2013 May 8 [cited 2020 May 2]. https://media.tghn.org/articles/3._CONSISE_nCoV_Serial_cross-sectional_seroprevalence_protocol_8May2013_1.pdf.
  9. Centers for Disease Control and Prevention. Washington, D.C.: U.S. Department of Health and Human Services. CDC newsroom: coronavirus disease 2019 (COVID-19); [cited 2020 May 5]. https://www.cdc.gov/media/dpk/diseases-and-conditions/coronavirus/coronavirus-2020.html.
  10. Sood N, Simon P, Ebner P, Eichner D, Reynolds J, Bendavid E, Bhattacharya J. Seroprevalence of SARS-CoV-2–specific antibodies among adults in Los Angeles County, California, on April 10-11, 2020. JAMA. 2020 May 18;e208279.
  11. Los Angeles County Department of Public Health. Los Angeles (CA): Los Angeles County Department of Public Health. COVID-19 surveillance dashboard; [cited 2020 May 24]. http://dashboard.publichealth.lacounty.gov/covid19_surveillance_dashboard/; because the infection percentage from Table 1 was calculated by dividing the cumulative sum of positive specimens by the number of total specimens collected between April 10 and April 14, 2020, (i.e., the average infection percentage for the span), the CFR is calculated based on total deaths reported until April 12, the middle day of the span.
  12. Bendavid E, Mulaney B, Sood N, Shah S, Ling E, Bromley Dulfano R, Lai C, Weissberg Z, Saavedra-Walker R, Tedrow J, Tversky D, Bogan A, Kupiec T, Eichner D, Gupta R, Ioannidis J, Bhattacharya J. COVID-19 antibody seroprevalence in Santa Clara County, California. Medrxiv [Preprint]. 2020 Apr 30 [cited 2020 May 19]. https://www.medrxiv.org/content/10.1101/2020.04.14.20062463v2.full.pdf; CFR is calculated based on total deaths and antibody results reported in the study.
  13. Miami-Dade County Office of the Mayor. Second round of COVID-19 community testing completed; Miami-Dade County and the University of Miami Miller School of Medicine announce initial findings. Miami-Dade County news release; 2020 Apr 24 [cited 2020 19 May]. https://www.miamidade.gov/releases/2020-04-24-sample-testing-results.asp.
  14. Florida Division of Emergency Management. Tallahassee (FL): Florida Division of Emergency Management. Coronavirus: summary of persons being monitored, persons under investigation, and cases; 2020 May 18 [cited 2020 May 19]. https://floridadisaster.org/globalassets/covid19/dailies/covid-daily-report-5.18.20-.pdf (42-50 p); because the infection percentage from Table 1 was calculated by dividing the cumulative sum of positive specimens by the number of total specimens collected between April 10 and April 24, 2020, (i.e., the average infection percentage for the span), the CFR is calculated based on total deaths reported until April 17, the middle day of the span.
  15. Arizona Department of Health Services. Phoenix (AZ): Arizona Department of Health Services. Data dashboard; [cited 2020 May 15]. https://www.azdhs.gov/preparedness/epidemiology-disease-control/infectious-disease-epidemiology/covid-19/dashboards/index.php (click on Laboratory Testing); CFR is calculated using antibody tests from specimens collected between April 26 and May 10, 2020.
  16. Arizona Department of Health Services. Phoenix (AZ): Arizona Department of Health Services. Data dashboard; [cited 2020 May 24]. https://www.azdhs.gov/preparedness/epidemiology-disease-control/infectious-disease-epidemiology/covid-19/dashboards/index.php (click on COVID-19 Deaths); because the infection percentage from Table 1 was calculated by dividing the cumulative sum of positive specimens by the number of total specimens collected between April 26 and May 10, 2020, (i.e., the average infection percentage for the span), the CFR is calculated based on total deaths reported until May 3, the middle day of the span.
  17. Coronavirus antibodies present in nearly 25% of all NYC residents, Cuomo says; un-pause in certain regions of NY might begin in May. CBS New York; 2020 Apr 27 [cited 2020 May 19]. https://newyork.cbslocal.com/2020/04/27/coronavirus-antibodies-present-in-nearly-25-of-all-nyc-residents/.
  18. New York City Department of Health and Mental Hygiene. New York City: New York City Department of Health and Mental Hygiene. Coronavirus disease 2019 (COVID-19) daily data summary; 2020 Apr 23 [cited 2020 May 19]. https://www1.nyc.gov/assets/doh/downloads/pdf/imm/covid-19-daily-data-summary-deaths-04242020-1.pdf; because the infection percentage from Table 1 was calculated by dividing the cumulative sum of positive specimens by the number of total specimens collected between April 20 and April 27, 2020, (i.e., the average infection percentage for the span), the CFR is calculated based on total deaths reported until April 23, the middle day of the span.
  19. World Health Organization. Geneva (Switzerland): World Health Organization. WHO Director-General’s opening remarks at the media briefing on COVID-19—3 March 2020; 2020 Mar 3 [cited 2020 May 17].https://www.who.int/dg/speeches/detail/who-director-general-s-opening-remarks-at-the-media-briefing-on-covid-19—3-march-2020.
  20. Ferguson NM, Laydon D, Nedjati-Gilani G, Imai N, Ainslie K, Baguelin M, Bhatia S, Boonyasiri A, Cucunubá Z, Cuomo-Dannenburg G, Dighe A, Dorigatti I, H Fu, Gaythorpe K, Green W, Hamlet A, Hinsley W, Okell LC, van Elsland S, Thompson H, Verity R, Volz E, Wang H, Wang Y, Walker PGT, Walters C, Winskill P, Whittaker C, Donnelly CA, Riley S, Ghani AC. Report 9: impact of non-pharmaceutical interventions (NPIs) to reduce COVID-19 mortality and healthcare demand. London (UK): Imperial College London; 2020 Mar 16 [cited 2020 May 27]. https://www.imperial.ac.uk/media/imperial-college/medicine/sph/ide/gida-fellowships/Imperial-College-COVID19-NPI-modelling-16-03-2020.pdf.
  21. Fink S. Worst-case estimates for U.S. coronavirus deaths. New York Times; 2020 Mar 13 [updated 2020 Mar 18; cited 2020 May 2]. https://www.nytimes.com/2020/03/13/us/coronavirus-deaths-estimate.html.
  22. Centers for Disease Control and Prevention. Washington, D.C.: U.S. Department of Health and Human Services. Disease burden of influenza; [cited 2020 May 14]. https://www.cdc.gov/flu/about/burden/index.html.
  23. Davis LE, Caldwell GG, Lynch RE, Bailey RE, Chin TD. Hong Kong influenza: the epidemiologic features of a high school family study analyzed and compared with a similar study during the 1957 Asian influenza epidemic. Am J Epidemiol. 1970 Oct;92(4):240-7.
  24. Glezen WP. Emerging infections: pandemic influenza. Epidemiol Rev. 1996;18(1):64-76.
  25. Fauci AS, Lane HC, Redfield RR. Covid-19—navigating the uncharted. N Engl J Med. 2020 Mar 26;382(13):1268-69.

Note: Population estimates obtained from the U.S. Census Bureau.

These statements are intended for informational purposes only and should not be construed as personal medical advice.

© 2020 Physicians for Informed Consent, an independent 501(c)(3) nonprofit educational organization. Jun 2020.