Typical Progress of Covid-19

[Chart updated on October 8th, 2020]

In this chart, I describe the typical progress of the new coronavirus Covid-19 (or COVID-2019) aka 2019-nCoV. This chart is based on the average population in ideal conditions where everyone gets the best possible treatment.

By the average population I mean that the disease has spread evenly to all age groups in an average Western country (like Finland or Germany). This chart is meant to give you an idea how the new coronavirus Covid-19 will progress and approximately how many people will have different variations of the disease.

How many people will die?

If the disease is spread mainly among the younger generations, more people hardly notice that they’re infected and less people are hospitalized, need to go to the intensive care unit (ICU) or die.

If a country (or an area) has a high number of older people and the infection starts spreading among them, more people will have the severe form of the disease, need critical care and die.

When a country has reached a point where the space at the intensive care units (ICUs) is getting limited or nonexistent, the more people in critical condition will be denied access to ICUs and even hospitals. The result: more people in critical condition will die.

The number of asymptomatic cases?

One of the most uncertain numbers in my graph is the number of asymptomatic cases.

By asymptomatic cases, I mean people who don’t experience any discernable symptoms. Note the word ”experience”. Based on various reports I suspect that many people who feel like they don’t have any symptoms, just dismiss exhaustion, muscle aches and even a slight rise in the body temperature as something more benign like being stressed, having spent too much time in unergonomic position or the wrong room temperature.

Those few studies where a larger group of people without symptoms has been tested suggest that about 30–80 % of infected could be asymptomatic. That is a huge range and all the studies and reports I’ve seen have been more or less flawed.

Update (Oct 8th, 2020): the most recent data suggests that less than 40 % of infected people will stay truly asymptomatic.

The studies I’ve found rarely follow up with the tested people to see if they’ve got symptoms later or not. It takes on average 5–6 days for the symptoms to appear (range: 2–14 days). One can infect others and test positive for covid-19 up to 1–3 days before the first symptoms. So it is plausible that some of the people tested in various studies got symptoms a couple of days after being tested.

At the same time most studies end up testing adults and elderly people. Why? I have no idea. Maybe it has something to do with consent or study protocols?

It looks like children will get infected and will infect others just like adults – but their symptoms are much milder and vague – often even non-existent. If a study has tested only adults, it is very likely that its number of asymptomatic and mild cases is too low compared to the general population.

The only follow-up reporting for a larger group of people I’ve seen so far was for the cruise ship Princess Diamond (see below). The final percentage of asymptomatic patients of all the infected patients was at least 39%. But since the ”population” at the cruise ship was on average older than the general population in any country, that number is probably too low.

So my best guess is based on the information available on October 8th, 2020 and the studies/reports I present below that less than 40 % of people are asymptomatic. I’m convinced that if we count the kids, at least 30 % of people are asymptomatic.

Below are some studies and reports of asymptomatic people with covid-19:

Village of Vò

The whole population of 3300 people in the Italian village called Vò was tested after the first positive covid-19 test result. 89 people got a positive test result and was quarantined. 10 days later people were tested again. This time only 6 new infections were found. I haven’t been able to find the exact numbers for the asymptomatic patients, but according to this letter 50–75 % of them were asymptomatic.

Iceland

Iceland has tested both those who have a reason to believe they may have covid-19 and the general population to see how widely the virus has spread. They had tested by March 25 altogether 5 448 people who had no reason believe that they had covid-19. Out of them 52 turned out to have the new coronavirus – and 50 % of infected didn’t have any symptoms. That doesn’t mean that they couldn’t develop them after the testing, but since there was no follow-up, we can only speculate how many of them got the symptoms. (Source 1, source 2)

China

China began publishing also the number of asymptomatic cases on April 1st, 2020. According to an article published in BJM.com on April 2nd, 78 % of new covid-19 cases in China seem to be symptomless. Again – since these cases are so new, there’s no way of telling how many of them will go on develop symptoms.

An earlier analysis of 25 961 laboratory-confirmed cased in Wuhan showed that at least 59 % of those cases were unascertained, which could mean that they were asymptomatic or mild-symptomatic cases.

Princess Diamond

Some people and sources claim that only 17.9% of cases would be asymptomatic because this Eurosurveillance study of Diamond Princess estimated so. First, that number was based on mathematical calculations, not on actual cases. Second, the calculations were based on the old number of positive tests (634 vs the actual number: 712).

At the time of testing about 46,5 % of the infected people on Princess Diamond were asymptomatic. Since at first only the symptomatic people were tested, it is possible that some people had before testing already had an asymptomatic version of covid-19. It seems that especially the crew was tested only towards the end of the ship being in quarantine – by the time most infected people would have had symptoms.

The Japanese Health Authority did the last follow-up on the Diamond Princess passengers on March 15. According to the latest information at least 279 of the passengers who tested positive were asymptomatic (39% of all the infected patients). That excludes those who returned to their home countries on chartered flights – so the actual number might be higher. (Source)

Hospitalization, ICU and death rates

The percentages of hospitalizations, ICU patients, and death rates vary from country to country based on demographics, health care system and who will get infected.

The older people are, the more likely it is that they’ll get the more severe version of Covid-19 and die of Covid-19.

The quality of the health care system and/or the treatment methods/protocols used in hospitals/country may impact the death rates as well.