Charts Explaining the Coronavirus Death Rate—and Why It's Definitely Not 'Just a Flu'

The avalanche of coronavirus infections in the current pandemic has been accompanied by a similar avalanche of information, making it hard to sift reliable news from the noise.

Among the most crucial questions is: how deadly is the SARS-CoV-2 virus that causes COVID-19?

First things first: contrary to some reports, there is no evidence the virus has evolved a new, deadlier strain since it emerged in late 2019. Of course, all viruses evolve, and SARS-CoV-2 is no exception, but reports of an aggressive new strain have now been retracted.

SARS-CoV-2 seems to be mutating (undergoing genetic changes) at a similar rate to other coronaviruses, such as the 2002 SARS virus and the virus that caused Middle East Respiratory Syndrome in 2012.

This is less than half the rate at which influenza viruses typically mutate, which itself is slow enough to allow the production of annual flu vaccines.

coronaviurs evoultion
Evolutionary rates for three coronaviruses, including SARS-CoV-2 that causes COVID-19. Higher values indicate viruses that accumulate mutations faster; error bar around SARS-CoV-2 indicates current uncertainty. Taiaroa et al. 2020 / Sebastian Duchene Univ. Melbourne

So how deadly is it?

This question is much more relevant, but less straightforward to answer.

Reports of the virus's lethality vary by an order of magnitude. While most people manage to recover from COVID-19, a significant proportion succumb to direct viral damage, pneumonia and sepsis.

On March 3 the World Health Organization stated the death rate was 3.4 percent. Other widely quoted estimates have put the figure at 3 percent or 5 percent. But other sources have estimated it at well under 1 percent.

One reason for these discrepancies is that they often use two different ways to calculate the death rate.

The Case Fatality Rate (CFR) is the number of deaths divided by the number of known infections. This figure can be greatly biased upwards or downwards due to sampling.

Imagine the virus infects 100 people; 70 are asymptomatic and unaware of their infection, while 30 fall sick and are diagnosed, and one of these 30 people dies.

In this example the true death rate is 1 percent (1/100), but the CFR is 3.3 percent (1/30).

This bias is often strongest during an outbreak's early stages, when many mild cases are missed and the number of confirmed cases is still low.

For this reason, some epidemiologists now think the initially reported death rates are severe overestimates.

There is a second measure we can use here, which corresponds more closely to most people's idea of "deadliness". The Infection Fatality Rate (IFR) is the number of deaths divided by the true number of infections, including both confirmed and undiagnosed cases. This statistic is harder to calculate, as it requires estimating the number of undetected infections.

case fatality
Case Fatality Rate is the number of deaths divided by the number of known cases. Infection Fatality rate is the number of deaths divided by all infections (known cases plus unknown instances). Michael Lee Flinders Univ. & SA Museum

One estimate of the IFR for COVID-19 puts this figure at 1 percent, and some new data suggests this is credible.

As testing becomes more rigorous, the discrepancy between the two measures (CFR and IFR) gets smaller. This may be happening in South Korea, where exhaustive testing has detected many mild infections and pushed the estimated death rate down to 0.65 percent.

Similarly, the stricken cruise ship Diamond Princess is illuminating because the rigorous quarantine meant nearly all COVID-19 cases—even asymptomatic ones—were identified. There were seven deaths among more than 600 infections, giving an IFR of about 1.2 percent. This is higher than in South Korea, but perhaps expectedly so, given that one-third of the ship's passengers were aged over 70.

Still not 'just a flu'

Even a 1 percent death rate is extremely disturbing. Newly released projections suggest 20-60 percent of Australians could contract the coronavirus, which would translate to 50,000-150,000 deaths.

By comparison, an estimated 35 million Americans caught the flu last year, with 34,000 deaths: less than 0.1%. The coronavirus is much deadlier than seasonal flu, particularly for older people, and there is no vaccine.

Because the virus hits old people hardest, countries with ageing populations will be more severely affected. Based purely on demographics, the projected death rate in Italy is seven times the rate in Niger; Australia is worse than the global average. Of course, the eventual death rates will also depend on countries' health systems and containment responses.

death rates coronavirus
Projected death rates (global, and by country) from COVID-19. Based on CFR data from March 13, 2020. / Michael Lee, Flinders Univ. & SA Museum

This age-selective mortality of COVID-19 should be explicitly considered in plans to combat it. In Australia, 11 percent of the population are over 70 and are predicted to account for 63 percent of deaths. Insulating a relatively small proportion of elderly people will halve deaths and is potentially more practical than total lockdown of entire populations. We need to urgently focus on the best way to achieve this. At the time of writing, the U.K. is seriously discussing this strategy.

There is a disturbing flipside to the fatality rate being lower than initially reported: each death implies a much greater number of circulating infections. Most COVID-19 deaths occur at least two weeks after infection. So a single death today means that around 100 people were already infected two weeks ago, and that number has likely increased exponentially to several hundred by today.

The implication is stark. We cannot wait until multiple people die in a COVID-19 cluster before enforcing extreme containment measures. By then the outbreak will already be extremely large and challenging to manage.

Views expressed in this article are the authors' own.

Mike Lee is Professor in Evolutionary Biology (jointly appointed with South Australian Museum) at Flinders University and Sebastian Duchene is ARC DECRA Fellow at the University of Melbourne, Australia.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The Conversation

World Health Organization advice for avoiding spread of coronavirus disease (COVID-19)

Hygiene advice

  • Clean hands frequently with soap and water, or alcohol-based hand rub.
  • Wash hands after coughing or sneezing; when caring for the sick; before; during and after food preparation; before eating; after using the toilet; when hands are visibly dirty; and after handling animals or waste.
  • Maintain at least 1 meter (3 feet) distance from anyone who is coughing or sneezing.
  • Avoid touching your hands, nose and mouth. Do not spit in public.
  • Cover your mouth and nose with a tissue or bent elbow when coughing or sneezing. Discard the tissue immediately and clean your hands.

Medical advice

  • If you feel unwell (fever, cough, difficulty breathing) seek medical care early and call local health authorities in advance.
  • Stay up to date on COVID-19 developments issued by health authorities and follow their guidance.

Mask usage

  • Healthy individuals only need to wear a mask if taking care of a sick person.
  • Wear a mask if you are coughing or sneezing.
  • Masks are effective when used in combination with frequent hand cleaning.
  • Do not touch the mask while wearing it. Clean hands if you touch the mask.
  • Learn how to properly put on, remove and dispose of masks. Clean hands after disposing of mask.
  • Do not reuse single-use masks.