It was at a press conference that WHO Director General Tedros Adhanom Ghebreyesus found that Covid-19, the disease caused by the new coronavirus sars-cov-2, is more deadly but less contagious than regular flu.

- Globally, around 3.4 percent of the reported Covid-19 cases have died. In comparison, seasonal flu kills significantly less than 1 percent of those infected, said Tedros Adhanom Ghebreyesus.

3.4 percent mortality, a figure the organization also tweeted, is significantly higher than previous estimates for sars-cov-2.

"Yes, this is the first time we have put a figure on mortality," says Carla Drysdale of WHO.

The World Health Organization went out with the figure 3.4 percent on Twitter, which caused many followers to react. Some got scared, others questioned if the figure is relevant. Photo: Twitter

The fact that the WHO is higher than other studies is because their figure is based on a rough estimate calculated on the proportion of deceased per confirmed infected, a measure called CFR (case fatality rate). CFR should not be confused with mortality in an entire population.

- 3.4 percent is a snapshot globally of CFR. Early during an outbreak, the figure can be high as the most serious cases are caught. In China, the CFR has decreased dramatically since the outbreak, says Carla Drysdale.

The WHO thus admits itself that the figure they communicated outward is probably exaggerated. Despite this, the organization has chosen to compare apples to pears - the mortality rate in common flu to which WHO refers is measured over a longer period of time.

SVT News has for two days asked WHO to answer the question why they compare the two measures, if it is relevant and how they feel before people can be frightened. WHO has not returned.

The Public Health Authority refers to Chinese figures

Anders Tegnell, state epidemiologist at the Public Health Agency, expects that in the future we will get several different figures on how deadly the virus actually is.

- So it will be with all these new diseases, where you don't really know yet, he says.

The large - and unknown - variable that will affect the estimated mortality of Covid-19 is the large number of people who are infected with sars-cov-2 without any symptoms.

- The best figure is still the one we got from the big Chinese study. There, there was a mortality rate of just over 2 percent of people seeking medical care. At the same time, we must remember that there are also obviously very many who do not seek medical care, so the actual figure is considerably lower, he says and continues:

- I saw some figure quite recently where they had calculated this and they said that we can expect a population-level mortality rate of 0.7-0.8 percent.