Covid was 24 times more deadly than flu in the first wave

No matter how you look at it, Covid-19 is not a flu. Of the people who got a covid infection in the first wave, 1.2 percent died. The so-called infection-fatality ratio (IFR) of Covid-19 is many times higher than the mortality risk from seasonal flu in the Netherlands, which is estimated at 0.05 percent. That percentage decreased in the second and third waves, especially when the vaccines became available in 2021.

Researchers from four Dutch universities and RIVM calculated the risk of hospital and IC admissions and death in the first three waves of the pandemic, per age group. Their study appeared on a preprint server on Friday and has yet to be evaluated by independent scientists.

The mortality rate of Covid-19 has been under discussion since the outbreak. The figure is difficult to estimate early in an outbreak; To be able to calculate it properly, solid data is needed, so an epidemic must have been going on for some time.

For the mortality figures, RIVM drew on data from Statistics Netherlands. The researchers estimated the number of infected on the basis of data on antibodies in the blood, instead of on the basis of the number of infections reported from the PCR tests. RIVM regularly measures these antibodies with a random sample. “That is a strong point of the research,” says Alma Tostmann, epidemiologist at RadboudUMC in Nijmegen. “This makes it possible to estimate the number of infections more accurately.”

A rough measure

The researchers used the pandemic excess mortality figures as a measure of covid mortality. “That is a rough measure,” says Tostmann, “because that group of excess mortality consists of several components. The expected mortality may also have been different during the pandemic: for example, there was no flu going around and the healthcare system was overloaded.”

The researchers looked at hospital and ICU admissions and deaths from Covid-19 against the number of people who had contracted an infection. They did this for the first wave (spring 2020), the second wave (fall 2020 to February 2021) and the third wave (March to June 2021).

The risk of hospitalization averaged 1.5 percent in the first wave and increased slightly in the later waves when many more people became infected. The risk of an ICU admission remained the same during the three waves, at 0.36 percent.

The percentage of people who died after a corona infection averaged 1.2 percent for the entire population in the first wave. That percentage increased sharply with age. In the first and second wave, the risk of dying after an infection was around 0.1 percent for people in their fifties, 1 percent for people in their sixties, 5 percent for people in their seventies, and more than 10 percent for people in their eighties. In the third wave, when the vaccines were just available and many elderly people had been vaccinated in the weeks before, mortality among people in their eighties fell sharply, to 1 percent.

A quick calculation

With these percentages, the mortality risk in the first three waves is higher than that of the flu (influenza). In a 2010 Nivel report, researchers calculated an IFR for influenza in the Netherlands of 0.3 percent, 2.5 percent and 5.5 percent, respectively for the age groups of 0-19 years, 50-64 years and 65 years and older. When asked, using a quick calculation, epidemiologist John Paget of research institute Nivel arrives at an even lower IFR for influenza in the Netherlands: an average of 0.05 percent, and 0.5 percent for the over-65s.

Over the course of the pandemic, the average IFR of Covid-19 decreased: in the second wave it was 0.83 percent, in the third it was 0.19 percent. The lower rate in the second wave is because when many more younger people contracted Covid-19, the authors believe. Mortality among them is lower. In the third wave, the average mortality rate was even lower, thanks to the vaccinations.

Covid-19 is therefore not ‘just a flu’, concludes Tostmann. “It is also too limited to only look at mortality. Of course, thanks to all the immunity and with the omikron variant, the picture is now more favorable. The numbers of people who have ended up in hospital with Covid-19 in recent months are still high, even with vaccinations. The flu can’t do that, the flu season is also much shorter. And the proportion of people who survive lung covid from an infection is much larger. That cannot be compared to what you see with influenza.”