Mortality describes being mortal and therefore destined to die and mortality rate refers to the number of deaths in a population. Mortality or death is an important measure to assess the severity of the impact of diseases on populations.
Two measures of mortality are used to assess what proportion of those infected with SARS CoV-2 dies of COVID-19:
1. Case Fatality Ratio (CFR) is an estimate of the proportion of deaths among identified confirmed cases.
2. Infection Fatality Ratio (IFR) is an estimate of the proportion of deaths among all infected individuals.
The IFR has a large denominator of everyone infected and is a much smaller figure. The CFR has a smaller denominator of only those who are ill, actual confirmed cases, and would therefore be higher than the IFR.
During the early stages of the pandemic, the IFR of SARS-CoV-2 was likened to that of seasonal flu, to be around 0.1%. That means COVID-19 would probably kill one out of every 1000 people infected.
The infection fatality ratio (IFR) of SARS-CoV-2 is difficult to estimate because the total number of diagnosed and undiagnosed cases is needed as the denominator.
The more accurate the estimate of the numbers of people infected with SARS-CoV-2, the more reliable the IFR. However, the detection of infected people is often underestimated as:
- many are asymptomatic or only have mild symptoms so don’t seek health care and don’t get tested.
- testing for the virus may also be inadequate in marginalised and underserved populations
- the number of tests and capacity may be limited and are reserved for high-risk groups, and
- people who have the infection may also be misdiagnosed as having influenza or a similar condition.
The Johns Hopkins University website provides country-specific fatality ratios of COVID-19.
Epidemiology Infectious Disease