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Thursday, October 27th, 2022, 5:07 pm

Pre-vaccine fatality rates lower than previously thought


Lower than previously thought

Impact of non-pharmaceutical interventions (NPIs) to reduce COVID-19 mortality and healthcare demand (16th March 2020)

Imperial College COVID-19 Response Team

We assumed

Incubation period of 5.1 days

Infectious 12 hours before to 4.6 days after


Non-uniform attack, applied to the GB population

Result in an IFR of 0.9%

with 4.4% of infections hospitalised

10.4 day stay

30% of hospitalised, ICU (50% death rate)

(not accounting for the potential negative effects of health systems being overwhelmed on mortality)

Age-stratified infection fatality rate of COVID-19 in the non-elderly informed from pre-vaccination national seroprevalence studies

Stanford California, Rome, Montreal

40 eligible national seroprevalence studies,

covering 38 countries with pre-vaccination seroprevalence data.

For 29 countries publicly available age-stratified COVID-19 death data,

and age-stratified seroprevalence information were available,

and were included in the primary analysis.

IFRs for 0 to 59 years

median IFR = 0.035%

(IQR, 0.013 – 0.056%)

Without accounting for seroreversion

(average time from seroconversion to seroreversion at 3-4 months)

IFRs for 0 to 69 years

IFR = 0.095%

0 to 19 years

IFR = 0.0003%

20 to 29 years

IFR = 0.003%

30 to 39 years

IFR = 0.011%

40-49 years

IFR = 0.035%

50-59 years

IFR = 0.129%

60-69 years

IFR = 0.501%

At a global level

Pre-vaccination IFR,

may have been as low as,

0 to 59 years = 0.03%

0 to 69 years = 0.07%

Global population

94% younger than 70 years

91% younger than 65 years

86% younger than 60 years

The current analysis suggests a much lower pre-vaccination IFR in non-elderly populations than previously suggested.

Large differences did exist between countries and may reflect differences in comorbidities and other factors.

These estimates provide a baseline from which to fathom further IFR declines with the widespread use of,


Prior infections

Evolution of new variants.

Unmitigated epidemic
(March 2020)
UK deaths = 510,000 (168,913)

US deaths = 2.2 million (1,065,152)

During 2021 and 2022

Vaccination, new variants, prior infections,

resulted in a marked decline in the IFR

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