SARS-Cov-2 and Infection Fatality Rates
The infection fatality rate (IFR), defined by the number of COVID-19 associated deaths divided by the total number of infections – Is one of the most important and reliable sources of information to understand the severity of any infectious epidemics. In contrast to the case fatality rate (CFR), the IFR is not only based on the number of confirmed cases (that now clearly are shown to be highly unreliable) and should therefore not be biased by potential drifts and variations in testing policies. However, as the total number of infections with SARS-CoV-2 is generally unknown, the IFR can only be estimated based on available surveillance and seroprevalence data.
COVID-19 antibody seroprevalence in Santa Clara County, California
Covid-19 antibody seroprevalence was investigated early in the SARS-CoV-2 viral outbreak. 3328 county residents were tested for immunoglobulin G (IgG) and immunoglobulin M (IgM) antibodies to SARS-CoV-2 using a rapid lateral-flow assay (Premier Biotech).
After adjusting for test-performance characteristics and weighting for county demographics, it was estimated that the seroprevalence of antibodies to SARS-CoV-2 in Santa Clara County in late March 2020 was 2.76%, with uncertainty bounds from 1.32% to 4.22%. The most important implication of these findings early in the pandemic, was that the number of infections was much greater than the reported number of cases. The estimated infection fatality rate was estimated to 0.17% (read more here).
5 months into the pandemic Stanford’s John P.A. Ioannidis identified 36 studies (43 estimates) along with additional 7 preliminary national estimates (50 pieces of data) and concluded that among people <70 years old across the world, infection fatality rates ranged from 0.00% to 0.57% with a median of 0.05% across the different global locations (with a corrected median of 0.04%). These are data that area comparable to the common flu.
His the most comprehensive review of the Infection Fatality Rate of Covid-19 – SARS-Cov2 inferred from seroprevalence data found that from 61 studies (74 estimates) and eight preliminary national estimates seroprevalence estimates ranged from 0.02% to 53.40%. Infection fatality rates ranged from 0.00% to 1.63%, corrected values from 0.00% to 1.54%. Across 51 locations, the median COVID-19 infection fatality rate was 0.27% (corrected 0.23%): the rate was 0.09% in locations with COVID-19 population mortality rates less than the global average (< 118 deaths/million), 0.20% in locations with 118–500 COVID-19 deaths/million people and 0.57% in locations with > 500 COVID-19 deaths/million people. In people younger than 70 years, infection fatality rates ranged from 0.00% to 0.31% with crude and corrected medians of 0.05%. Read more here.
Among the elderly twenty-three seroprevalence surveys representing 14 countries were included. Across all countries, the median IFR in community-dwelling elderly and elderly overall was 2.4% (range 0.3%-7.2%) and 5.5% (range 0.3%-12.1%). IFR was higher with larger proportions of people >85 years. Younger age strata had low IFR values (median 0.0027%, 0.014%, 0.031%, 0.082%, 0.27%, and 0.59%, at 0-19, 20-29, 30-39, 40-49, 50-59, and 60-69 years).
SARS-Cov-2 and Excess Mortality
Due to the problems associated with the diagnosis of Covid-19 deaths with unreliable PCR tests, European countries recommend monitoring the overall mortality and the so-called excess mortality with reporting at least once a week. Tracking all deaths provides a more comprehensive picture of the extent of mortality and enables comparisons in time and place.
From week 9 to 30, you see an increase in excess mortality in the US and Europe by 17% and 15% from an average. Spain had the highest mortality rate with just under 30% followed by England and Wales (27%)
Cumulative P-scores of excess mortality comparing the US to Europe, weeks 9 to 30
From the European Monitoring of Mortality Project hosted by the Serum Institute of Copenhagen, Denmark we can follow the Covid-19 epidemic from its emergence in the early spring of 2020 to date with comparisons back to 2016 in 28 countries of Europe that report mortality data on a weekly basis giving the most comprehensive overview of survival compared to seasonal influensa outbreaks by country and age groups.
From this graph (Euromomo updated to 17.09. 2021) we can see that excess mortality in Europe rose steeply like a spike in the spring of 2020 and rapidly fell to comparable numbers of former years. The second wave is more comparable to 2018 -2019 influensa season.
After one year of observation, the Centers for Disease Control and Prevention (CDC) on February 20, 2021 reported that in the U.S. 376,504 deaths were attributed to COVID-19 in the United States in the calendar year 2020. This figure is well below that estimated for the total number of U.S. deaths from excess mortality (seasonal influenza) in 2017. The comparison becomes more striking when comparing lost life-years. Goldstein and Lee estimate that the average loss of life for a person who dies from COVID-19 in the United States is 11.7 years. Multiplying 377,000 decedents by 11.7 y lost per decedent gives a total of 4.41 lost life years from COVID-19 in 2020, which is then only a third of the 13.02 million life years lost to excess mortality in the US in 2017. This is due to a significantly higher average age for COVID-19 deaths in 2020 than the average age for excess mortality in 2017 due to flu-like illness and a dramatic increase in risk of death with age for those over 85 years of age.
In the UK we find similar comparisons with the excess mortality in 2017 being greater than in 2020 and greater life-years lost with the higher average age of COVID-19 deaths.
References: