Studies on Covid-19 lethality

Published: May 12, 2020; Last updated: August 5, 2020
Share on: Twitter / Facebook; Main article: Facts about Covid-19

Overview: 1) Immunological studies; 2) Antibody studies; 3) PCR studies; 4) Modelling studies; 5) Other studies; 6) Age of death; 7) Hospitalization rate; 8) Nursing homes; 9) Overall mortality; 10) Development of the pandemic. IFR: Infection fatality rate (population-adjusted).

1) Immunological studies

Immunological research indicates that serological antibody studies, which measure antibodies in the blood (IgG and IgM) and typically found population-based IFR values between 0.1% and 0.5% (see below), may detect only about 20% of infections, as most people neutralize the coronavirus with their mucosal (IgA) or cellular (T cells) immune system while developing only mild symptoms or no symptoms. This means IFR values may drop by a factor of five to values at or below 0.1%.

See also: Coronavirus likely five times more common and less deadly than assumed

Country Published Focus Factor Source
Switzerland May 23 IgA 5 Report / Study
China June 16 IgG 6 Report / Study¹
Germany June 16 T-cells 81% Study²
France June 22 T-cells 75% Study
Sweden June 29 T-cells 3 Study
Spain July 6 IgG 5 Study³
UK July 23 IgG 60% Study4

1) Only 16% of likely infected HCW had IgG; 2) 81% of unexposed individuals had cross-reactive T-cells; 3) Less than 20% of symptomatic individuals had IgG antibodies; 4) 60% cross-reactive IgG in children.

2) Antibody seroprevalence studies

Population-based antibody seroprevalence studies.

Country Published Population IFR (%) Source
Austria June 25 Ischgl hotspot <0.26 Report
Global June 8 23 studies
Below 70 years
Germany May 4 Heinsberg hotspot <0.36² Study
Iran May 1 Guilan province <0.12 Study
USA April 30 Santa Clara County 0.17 Study
Denmark April 28 Blood donors (<70y) 0.08 Study
USA April 24 Miami-Dade County <0.18 Report
USA April 21 Los Angeles County <0.20 Study

1) Median value; 2) The adjusted IFR is 0.27% (page 9). Note: Some of these studies are preprints.

3) Controlled PCR studies

Controlled PCR studies in population subgroups.

Country Date Population Cases IFR (%) Source
Germany July 25 Meat factory 1766 0.00 Study
France May 21 Health workers 28050 0.05 Study
USA May 10 MLB employees 5603 0.00 Report
France May 10 Aircraft carrier 1046 0.00 Report
USA May 10 Aircraft carrier 1156 0.09 Report
USA May 1 Tennessee prison 1349 0.00 Report
Italy April 28 Health workers 26657 0.30¹ Study
USA April 17 Boston homeless 146 0.00 Report
USA April 17 Boston blood donors 200 0.00 Report
Greece April 16 Repatriations 40 0.00 Study
USA April 13 NYC pregnant women 215 0.00 Study
Ship March 17 Diamond Princess 700 0.13² Study

1) See table below; 2) Age-adjusted IFR based on US population.

1) Deaths in Italian health care workers by age group (ISS, May 20)

4) Epidemiological models

Covid-19 IFR based on epidemiological models or predictions. These values are often somewhat higher than the actual values based on serological antibody studies (see above). In May 2020, the US CDC published a best estimate IFR of 0.26% (based on 35% asymptomatic cases).

Country Published Population IFR (%) Source
China July 16 Wuhan ~0.10 Study
USA May 20 CDC estimate 0.26¹ Study
France May 13 France 0.70 Study
Switzerland May 11 Switzerland 0.40 Study
UK May 7 UK 0.08² Study
France May 7 France 0.80³ Study
Global May 6 Metastudy 0.64 Study
Global May 5 Global 0.17 Study
India May 3 India 0.41 Study
April 20 Lombardia
New York City
China March 30 Mainland China 0.66 Study
China March 13 Wuhan city 0.12 Study
China March 9 Mainland China 0.50 Study

1) 0.4% symptomatic CFR and 35% asymptomatic cases; 2) Based on 29% prevalence and 50,000 deaths; 3) The IFR is 0.50 excluding nursing homes.

5) Additional antibody and PCR studies

These studies determine the prevalence of recent or current Covid-19 infections in a population or region. In most cases, they find that Covid-19 is much more widespread than previously assumed, with most people showing no or only mild symptoms.

Immunological research (see above) indicates that antibdody prevalence values may have to be multiplied by an additional factor of up to five to get the actual coronavirus prevalence values, because many mild cases neutralize the virus with their mucosal immune system.

Country Published Population Prev. Factor Source
Germany June 30 Blood donors 1.3%   Study
Russia June 10 Russia 14% 40x Report
USA May 15 Boston 12.5% 8x Report
Czech Rep. May 15 South Bohemia 5% 10x Report
USA May 13 Indiana 2.8% 11x Report
Spain May 13 Spain
10x Study
UK May 8 UK 29% 200x Study
Switzerland May 6 Geneva 9.7% 10x Study
Global May 5 < 65 years old     Study
Japan May 5 Kobe City 2.7% 396x Study
USA May 2 New York State
New York City
Spain May 2 Health workers 11.2%   Study
Netherlands April 29 Blood donors 2.7%   Study
France April 23 Northern France 3%   Study
USA April 19 Chelsea MA 32% 16x Report
Iceland April 14 Iceland (PCR) 0.8%   Study

6) Median age of Covid-19 deaths per country

Half of all deaths were below, half were above the median age.

Country Median age
Austria 80+ years EMS
Canada 86 years HCSC
England 80+ years NHS
France 84 years SPF
Germany 82 years RKI
Italy 81 years ISS
Spain 82 years MDS
Sweden 86 years FOHM
Switzerland 84 years BAG
USA 78.5 years CDC
Example: Death rate by age group in Massachusetts (Source)

7) Hospitalization rate

Initial estimates based on Chinese data assumed a very high 20% hospitalization rate, which led to the strategy of ‘flattening the curve’ to avoid overburdening hospitals. However, population-based antibody studies (see above) have since shown that actual hospitalization rates are close to 1%, which is within the range of hospitalization rates for influenza (1 to 2%).

The US CDC found that Covid-19 hospitalization rates for people aged 65 and over are “within ranges of influenza hospitalization rates”, with rates slightly higher for people aged 18 to 64 and “much lower” (compared to influenza) for people under 18.

In local hotspots like New York City, the overall hospitalization rate based on antibody studies is about 2.5% (19.9% or 1.7 million people with antibodies and 43,000 hospitalizations by May 2).

The much lower than expected hospitalization rate may explain why most Covid-19 ‘field hospitals’ even in hard-hit countries like the US, the UK and China remained largely empty.

8) Percentage of Covid-19 deaths in care homes

In many countries, deaths in care homes account for 30 to 60% of all additional deaths. In Canada and some US states, care homes account for up to 80% of all “Covid19-related” deaths. In Sweden, deaths in nursing homes plus nursing apartments account for 75% of all deaths.

Care home deaths: absolute numbers (bars, left scale) and percentages (dots, right scale)

Source: Mortality associated with COVID-19 outbreaks in care homes (LTC Covid, May 21, 2020)

Source: The Covid-19 Nursing Home Crisis by The Numbers (Freopp, June 19, 2020)

9) Overall mortality

In countries like the US, the UK, and also Sweden (without a lockdown), overall mortality since the beginning of the year is in the range of a strong influenza season; in countries like Germany, Austria and Switzerland, overall mortality is in the range of a mild influenza season.

Sources: US, UK-1, UK-2, Sweden, Switzerland, Germany

A comparison between the number of coronavirus deaths predicted by the influential model of Imperial College London (no measures or moderate measures) and the actual number of deaths in Sweden shows that the model strongly overestimated the impact of the epidemic:

Sweden: ICL model predictions versus actual Covid-19 deaths (HTY/FOHM)

10) Development of the pandemic

Even in countries without a lockdown, the epidemic reached its peak within a few weeks of the outbreak. However, many media showed cumulative deaths per day of report (left) instead of daily deaths per day of death (right), falsely implying an ever escalating situation.

Cumulative deaths per day of report vs. daily deaths per day of death. (OWD/FOHM; April 24)

See also

Main article: Facts about Covid-19

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