The mortality rate of COVID-19 remains high, but not as high as its transmission rate, and this good news needs nuances and explanations.
Data and statistics about COVID-19 cases are constantly streaming into the public space. They are being dissected, politicised and interpreted in countless ways. The same indicators seem to say different things, handled by counterparts that have divergent opinions.
Authorities often communicate long lists of figures, rather than explaining as clearly as possible what those numbers mean and putting them in the right context, writes Dr. Vlad Mixich, an independent expert of the board of the European Agency for Safety and Health at Work.
It happens even to the best of us to confuse indicators or use them interchangeably, but in order to have an accurate picture of COVID-19 mortality, we need to go through the context in which the figures are presented and know what each indicator measures.
Indicators that measure mortality from different angles
We have no perfect tool to compare the impact of the pandemic on different countries, therefore the number of deaths has been cited most often to show the extent of the crisis in different states, writes Dr. Kent Sepkowitz, an infectious disease specialist. However, the gross figure does not say much about the evolution of the pandemic in each country, given the differences in population size, which is why indicators are preferred to figures.
Two of the most used indicators are the infection fatality ratio (IFR), which represents the percentage of deaths caused by COVID-19 compared to the number of diagnosed people, and the case fatality rate (CFR), which expresses the proportion of deaths among all infected people, including the undiagnosed.
The case fatality rate may be important, for example, for an infected person who wants to know how high their probability of dying from COVID-19 is, Sepkowitz said. Anyone can easily calculate the indicator, averaging between the number of deaths in a country and that of the people diagnosed with COVID-19.
The disadvantage is that the CFR changes quite quickly in a pandemic, as the number of deaths or tests changes. In a situation where the numbers are changing so rapidly, such as a pandemic, the indicator probably does not accurately reflect the real risk of death of an infected person, write the editors of Our World in Data, emphasising that all that the CFR can do is reflect the severity of the disease at a certain time in a certain population.
In addition, data collected from the first cases of infection show that it can take between 2 to 8 weeks from the first symptoms to death, which means that, during an outbreak, the information is incomplete. During the 2002 SARS outbreak, the CFR was calculated at 3-5% in the early stages, but reached 10% in the end. Thus, calculations made in a certain phase can be confused with the final ones, underestimating the severity of the outbreak.
The infection fatality ratio (IFR) can be used to more accurately calculate the likelihood of death from COVID-19. The problem we encounter here is that the total number of cases of COVID-19 is unknown, therefore specialists estimate it in order to calculate the IFR. In July, the World Health Organization estimated that the infection fatality ratio was at about 0.6%.
The PLOS Medicine Journal recently published a study trying to answer the question of the best way to estimate the COVID-19 mortality rate.
Researchers at the University of Bern have developed a model for calculating the dynamics of the novel coronavirus transmission and its associated mortality, taking into account the period between infection and death, the rise of the number of severe symptoms cases and the data divided by groups of age. The conclusion was that the case fatality rate (CFR) is not a good predictor of overall mortality due to SARS-CoV-2, suggesting that the symptomatic case fatality rate (sCFR) and the infection fatality ratio (IFR) are better ways to monitor the epidemic. Thus, the study showed that, while CFR ranged in Europe from 3.9% to 17.8%, IFR estimates ranged from 0.5% to 1.4% (more information on COVID-19 mortality can be found in the article How deadly is COVID-19 and other (un)answered questions).
SARS-CoV-2, mutations and the power of contagion
While the discussion about the indicators used to measure mortality makes sense to the public only to the extent that it deciphers the different conclusions reached using different computational measures, the issue that concerns us all is whether mortality from SARS-CoV-2 is either increasing or decreasing. Of course, we also want to know how contagious the virus presently is.
In the first 6 months of the pandemic, researchers identified approximately 100 SARS-CoV-2 mutations. The question that worried everyone was whether, as it changes its characteristics, the virus becomes more or less harmful.
A strain of coronavirus (D614G) has become globally dominant since mid-March, and it was detected in 97% of the worldwide samples. An increasing number of researchers believe that the strain has a “selective advantage” over its original version, says Dr. Thushan de Silva of the University of Sheffield, explaining that there is not enough evidence to show that it is more contagious, although it is certainly “not neutral.”
Professor Bette Korber of the National Laboratory in Los Alamos, USA, pointed out that recent information makes the idea that the mutation has increased the viral load of patients less and less controversial. In fact, the dominance of the new strain may be an indication that the virus has become better at spreading from person to person than in the original version.
The risk of coronavirus remains very high, the World Health Organization said in a recent statement. The WHO’s emergency committee, who recently assessed the pandemic, said “its duration will certainly be very long.”
What happens to mortality?
Even if mortality seems quite low, the WHO considers that it is “still a high rate“, given the high transmission capacity of the virus. Mike Ryan, executive director of the WHO Department of Medical Emergencies, explained that it is a much deadlier virus than the flu virus: nearly 1 in 100 patients dies from COVID-19, while in the type-A flu pandemic of 2009, the mortality rate was 1 in 10,000.
More than a fifth of COVID-19 patients treated in German hospitals this year have died, according to a study by AOK’s WldO scientific research institute. Among mechanically ventilated patients, the mortality rate was 53%.
On the other hand, a British study published on June 30th in the journal Anesthesia showed that the mortality rate of COVID-19 patients admitted to intensive care has decreased by a third since the beginning of the pandemic. From over 50% in March, the COVID-19 mortality rate in intensive care units dropped to 42% in May, the study shows.
This is not just a decline in the UK, but a global phenomenon, and experts believe that the factors that explain this decline include a better understanding of COVID-19 symptoms and complications, improved treatment for more severe cases, and access to resources that were not available at the beginning of the pandemic.
Although this is good news, pulmonologist Jonathan Siner warns that we are still dealing with “a dangerous disease with regards to risk of death as well as more long-term risks of disability“.
The COVID-19 mortality rate of those admitted to intensive care (42%) is still double the mortality of other viral pneumonias, said Eric Cioe-Pena, director of Northwell Health in New Hyde Park, New York.
Although the growing number of cases could put pressure on the medical system, Siner remains optimistic, noting that mortality may continue to fall, as doctors gain more experience in the fight against COVID-19, and that steroids and remdesivir, drugs used to treat the disease, seem to have real benefits.
We cannot yet have all the data to clarify the decrease in mortality, but we should also take into account the gap between the increase in the number of infections, the increase in the number of severe cases, and the number of deaths. There could be several explanations on how mortality evolves, one of which is that the typical patient with COVID-19 is getting younger.
Need for caution
While the good news is followed by less good news in this new wave of the crisis, what has not changed is the need for caution and prevention. Even countries that thought they had overcome the worst of the pandemic are now struggling with a further increase in the number of cases of infection. The French Scientific Council, for example, warns in a document submitted to the government that the country is in a fragile state of control and can expect an uncontrolled resumption of the epidemic at any time. Melbourne, Australia’s second largest city, has imposed harsh restrictions to control a new wave of infections. The restrictions are felt by many as an unseen aerial bombardment that seems to never end, writes The New York Times.
“A miraculous solution” to the health crisis that the planet is facing may never be found, WHO Director-General Tedros Adhanom Ghebreyesus recently warned. And that is precisely because the road to normalcy could be long and difficult. Compliance with the already well-known sanitary measures remains the only weapon at hand.
By following prevention guidelines, we are actually doing everything we can to protect ourselves and our families, but also the community we belong to, says Dr. Penny Stern, director of the Department of Occupational Medicine, Epidemiology and Prevention in Northwell, New York, reminding us that this is a battle we are waging together rather than on our own.
Carmen Lăiu is a writer for ST Network and Semnele timpului.
