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Meta-Analysis Of Infection Fatality
Rates Confirms Increasing COVID Risk With Age
Results Explain
Why Overall Estimates Of IFR’s Have Varied So Widely
A report published
online in December in the European Journal of Epidemiology (EJE) has
reviewed data from 27 separate studies with seroprevalence data on
COVID-19 in surveys of representative populations in 34 separate
locations in the US, Canada, Asia, and Europe. Levin and colleagues
linked seroprevalence data with reported fatalities within 4 weeks to
estimate the risk of death from COVID-19.
Case Fatality Rate
While the link between
age and COVID-19 and severity has been widely reported based on the
Case Fatality Rate (CFR), the real risk of dying from COVID has
remained unclear because of a number of pitfalls surrounding the
development of the CFR. For example, asymptomatic cases have occurred
and case reporting has favored severe cases over milder or
asymptomatic cases. Also, testing availability has not been uniform
over time and place.
Levin and colleagues
sought to overcome these shortcomings by using seroprevalence studies
in numerous locations to calculate not the CFR but the Infection
Fatality Rate (IFR).
Infection Fatality
Rate
The IFR has been
calculated from other work and has been found to range from 1% in New
York City to a low of 0.6% in Geneva to a high of 2% in northern
Italy. According to Levin and colleagues “Such estimates have fueled
intense controversy about the severity of COVID-19 and the appropriate
design of public health measures to contain it, which in turn hinges
on whether the hazards of this disease are mostly limited to the
elderly and infirm. “
The variable estimates
for the overall IFR’s have led to the view that research on
age-stratified IFR’s is urgently needed to inform policy making
which was the goal of the work by Levin and colleagues. The IFR’s
estimated by them are included in the table below. A major conclusion
of the Levin group is that “about 90% of the variation in population
IFR across geographical locations reflects differences in the age
composition of the population and the extent to which relatively
vulnerable age groups were exposed to the virus."
Infection Fatality Rates
|
Age
|
Risk % |
Per
100,000 |
Increased
Risk Compared to Age 10 |
|
At 10 |
.002 |
2 |
--- |
|
At 25 |
.01 |
10 |
5X |
|
At 55 |
.04 |
40 |
20X |
|
At 65 |
1.4 |
1,400 |
700X |
|
At 75 |
4.6 |
4,600 |
2300X |
|
At 85 |
15 |
15,000 |
7500X |
The CFR overestimates the true risk of death because the number of
persons in the denominator is lower than it should be. Thus, the CFR
to IFR ratio varies by age because of the higher prevalence of
infections in the younger age groups. Thus, the ratio is 15:1 in the
30-49 year age group, about 7:1 for ages 50-69, and about 5:1 for ages
70-79, according to Levin and colleagues. ■
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