The true death rate of the coronavirus is still a mystery even as the global outbreak of the virus prepares to enter its fourth month.

Data from around the world suggests that 4.5 per cent of people who catch the coronavirus - one in every 22 patients - are dying of the disease.

There have been approximately 23,700 deaths recorded out of a total of 530,000 cases, according to today's data.

The true fatality rate is expected to be considerably lower but official numbers vary wildly from country to country because of how people get tested.

Italy, the worst affected country in the world, has a massive 11.3 per cent fatality rate - more than 9,100 people have died there.

This has been put down to the country's elderly population and the intensity of the epidemic in a relatively small area, which testing facilities have struggled to keep on top of.

Germany, meanwhile, has a very low death rate of just 0.62 per cent, with only 304 deaths out of nearly 50,000 patients. And this may be because the patients are younger and the country is more rigorously testing people who are only mildly ill.

Government testing regimes, which vary around the world, affect how good or bad a country's death rate looks.

A high number of patients compared to a low number of deaths will reduce the death rate, but if only people who are seriously ill are getting tested - as is the case in the UK, for example - the death rate will be higher than the reality because mild cases are not counted and a bigger proportion of those who are diagnosed will die.

The number of tests per person does not line up with countries' death rates, however, showing that other factors like hospital capacity and patient age are also important.

The current death rate in the UK is 5.21 per cent, with 759 fatalities out of 14,579 confirmed cases, but only hospital patients are now being tested.

A study of data from Wuhan, where the virus began, suggested that the true death rate of coronavirus patients is around 1.4 per cent - lower than World Health Organization estimates of 3.4 per cent.

Italy, the worst affected country in the world, has a massive 11.3 per cent fatality rate - more than 9,100 people have died there

Coronavirus death rates vary wildly across the world and are affected by a range of factors included the stage a country is at in its outbreak, how many people it tests and how much strain the health service is under

Italy's hospitals are overwhelmed, particularly in Lombardy where the country's outbreak began, meaning that the death rate is higher because people can't get quality healthcare

WHAT ARE CORONAVIRUS DEATH RATES AROUND THE WORLD? Italy - 10.19% (8,215 deaths) Spain - 7.55% (4,365 deaths) Netherlands - 5.81% (434) France - 5.74% (1,696) UK - 4.89% (578) Switzerland - 1.64% (194) US - 1.49% (1,271) South Korea - 1.49% (139) Germany - 0.59% (281) Austria - 0.57% (30) Australia - 0.33% (8) Advertisement

Professor Duncan Young, an intensive care expert at the University of Oxford, said a country's case fatality rate 'depends on the testing policy'.

He said: 'Testing more patients increases the denominator (people who have a positive coronavirus test) and so for a given number of deaths reduces the case fatality rate.'

Switzerland, a country of just 8.4million people, has one of the highest testing rates among nations with major outbreaks, testing 10.88 people per thousand of the population, according to most recent data.

It also has a low death rate - 1.68 per cent, with 207 deaths out of around 12,300 cases.

Meanwhile countries with death rates around five per cent - France (5.74), the UK (5.21) and the Netherlands (6.33) - have significantly lower testing capacity.

France, for example, is testing just 1.49 people per thousand; the UK is testing 1.59 per thousand; and the Netherlands is testing around 2.21 per thousand.

But broad testing does not ensure a death rate will stay low.

Italy and Spain have high testing rates - 5.79 and 7.1 tests per thousand people, respectively - but also have the highest death rates in the world.

Italy's death rate is said to be so high because the country has such an elderly population, with almost a quarter of people (22 per cent) aged 65 or older.

The elderly are more likely to die if they catch the coronavirus, statistics have shown.

And the country's outbreak exploded in a relatively small region in the north - Lombardy - quickly overloading hospitals and making patients more likely to die because they couldn't get the healthcare they needed.

WHY IS GERMANY'S DEATH RATE SO LOW? Germany has the lowest official coronavirus death toll of any country with a major outbreak, with fewer than one in 100 patients dying. Fast testing, younger patients and a late blooming outbreak may all be contributing to the country's apparentl resilience to COVID-19. Its fatality rate is just 0.62 per cent out of more than 49,000 cases. German authorities have been hot on testing people with only mild symptoms, Wired reports. This means that the vast majority of people in its official tally of patients will not die from the infection. At least 80 per cent of coronavirus patients can expect to have only mild symptoms, like a bad cold or flu, and to make a full recovery, scientists in the UK have said. The median (middle) age of the infected patients is also considerably lower than it is in Italy - 46 compared to 63 - reducing patient risk. Germany's hospitals also appear to be better prepared, according to Wired. It has 29.2 critical care beds per 100,000 people, compared to 12.5 in Italy. This ability to cope well with surging numbers of patients means the death toll is more likely to reflect the danger posed by the coronavirus rather than the danger of being admitted to an overloaded hospital. In Italy patients are dying because they can't get care. Germany's cases being spread out over a larger area could also contribute to less pressure on hospitals. Professor Michael Head, of Southampton, said 'There's a little bit of luck involved'. Advertisement

WHY IS ITALY'S DEATH RATE SO HIGH? Italy has the highest coronavirus death rate in the world with one in every 10 people who catch the disease there dying from it. Experts say having one of the oldest populations in the world, a large number of cases concentrated in a small area and inaccurate statistics are contributing to the deadly impact the virus is having there. At least 80,589 people have now been diagnosed with the virus and 9,134 are confirmed to have died. Its death rate is 10.19 per cent, according to the most recent data – the highest in the world. In China the death rate is around four per cent and scientists have suggested if that is higher than the true figure because many cases are likely to be going unreported. Italy has the biggest population of elderly people in Europe, with almost a quarter of people (22 per cent) aged 65 or older. And the median age of its coronavirus patients is 63, putting them at a higher than average risk of dying from the virus. As a result of a sudden, dramatic outbreak hospitals in the north are under immense pressure, which means patients may not get the high quality care they need and the virus could be more likely to spread in overloaded hospitals. Experts also say that the true number of cases is not being recorded in Italy because the infection is spreading so fast and people with mild illness may not be counted. Advertisement

It is not yet clear why Spain's death rate is so high (7.7 per cent) but it may be because the outbreak is escalating rapidly in its early stages without widespread testing to even out the spike in deaths over a large number of mild cases.

A fast spreading outbreak could, in another vein, also be the reason behind Germany's impressively low death rate.

German authorities have been fast to test people with even mild symptoms in the early stage of the outbreak, which builds up a buffer against a high death rate.

If officials are testing people who have the disease but aren't likely to die the data will be more accurate.

Testing before a surge in deaths could keep the death rate down, for example, while ramping up testing after a surge in deaths could mean the death rate stays high for longer.

Dr Steven Lawrence, a medicine professor at Washington University, told NPR: 'Case fatality rates have been very confusing... the numbers may look different even if the actual situation is the same.'

And Germany's death rate could also be artificially low because it is early on in its outbreak and it could take some time for critically ill patients to die.

Professor Martin Hibberd, from the London School of Hygiene and Tropical Medicine, told Wired: 'Germany's a little bit earlier on in the process than Italy.

'It takes two or three weeks of intensive care before people often succumb to the disease.'

Germany's hospitals may also be coping well with the surges in patients, whereas hospitals in Italy and Wuhan, for example, were completely overloaded.

Professor Hibberd added: 'Clearly, if you can't give intensive care to the most severely ill, then that will have an impact as well.

In Austria, another country with a low death rate (58 deaths from 7,500 people - 0.77 per cent), the age of the patients may be a contributing factor.

According to Professor Heinz Burgmann, at the MedUni Vienna, many of infections could be traced back to holidays in the Tyrol, a popular skiing region on the Italy/Austria border.

That meant they were among younger people who, when they returned, had not yet had time to infect many older people before movement restrictions started to come into place.

In Austria he said that most of those infected were in the age group 45 to 54, not in the 65+ risk group.

Thomas Czypionka, head of health economics at the Institute for Advanced Studies in Vienna, agreed.

He said: 'Those who go skiing are usually younger and have a better constitution.'

The skiier thesis could also explain the lower death rates in Germany and Norway, where it has become apparent that infection chains lead to the winter sports resorts.

Death rates of coronavirus may be HALF initial estimates by world health chiefs, promising study finds

The death rate of coronavirus may be half of what world health chiefs expected it to be, according to a study.

International researchers compiled data on coronavirus cases in Wuhan, the Chinese city of 11million people where the deadly disease emerged in December 2019.

They found that, overall, the number of people who died after getting sick with the coronavirus was 1.4 per cent.

In comparison, estimations by the World Health Organization in early March said 3.4 per cent of diagnosed patients had died.

And the true figure is likely to be even lower because so many people are believed to be going undiagnosed.

By comparison the death rate of flu is around 0.1 per cent.

Coronavirus patients often don't know they're infected – as many as eight out of 10 could have no symptoms in the early stages of an outbreak, according to one study –because they get such mild signs that they don't think anything of it.

The study, which has not yet been reviewed by scientists, came as more than 9,300 people around the world have died and more than 224,000 have been confirmed to be ill.

The death rate of coronavirus may be half that initially thought be world health chiefs, according to a study on Wuhan partients. Pictured, masked medical staff talking to a patient at Red Cross Hospital in Wuhan in China's central Hubei province on March 10

The preliminary findings come as the global death toll of COVID-19 nears 10,000, currently at 9,249, with more than 224,000 infected. A patient suffering from coronavirus disease (COVID-19) is seen in an intensive care unit at the Oglio Po hospital in Cremona, Italy

The study, led by Professor Joseph Wu of the University of Hong Kong, was focused on the city of Wuhan, where the first cases of COVID-19 were reported.

Professor Wu and colleagues from Harvard University used published data on 425 early confirmed cases and 41 fatalities in Wuhan.

But they wanted to get a bigger picture of how many people in the city, which is in the Hubei province, had the disease but showed no symptoms.

Hospitals had been overwhelmed in Wuhan and milder cases were unlikely to have been tested.

The team used a range of global data sources to estimate the full number of cases within Wuhan by taking into account the location and timing of cases outside of the area to work out how many people could be expected to have had it.

By studying real-life patients they found the average time from the start of symptoms – a fever or a cough – to death was 19 days, on average. It ranged between 16 and 24 days.

They worked out that the proportion of patients who died was 1.4 per cent, with a possible range from 0.8 per cent to two per cent.

WHAT ARE DEATH RATES OF OTHER VIRAL INFECTIONS? Mumps – 0.01% Flu – 0.1% Measles – 0.2% COVID-19 – 3.4% (estimated) Dengue fever – 5% with treatment Zika – 8.3% SARS – 10% Middle East Respiratory Syndrome (MERS) – 34% Ebola – 50% Sources: BMJ, WHO, MedScape, CDC Advertisement

For those aged 15 to 64 years, the average fatality rate was 0.5 per cent, with a reasonable range of between 0.2 per cent and 1.3.

Over 64s had a fatality rate of 2.7 per cent, with low and high estimates of 1.5 per cent and 4.7 per cent.

The findings support what officials have known for a long time – that the elderly are more at risk of death from COVID-19.

However, it is significantly below earlier estimates of two to three per cent death rate which had been predicted by the World Health Organization (WHO).

The WHO released a statement on March 3 that said: 'Globally, about 3.4 per cent of reported COVID-19 cases have died. By comparison, seasonal flu generally kills far fewer than one per cent of those infected.'

It is also lower than the four per cent death rate which divides deaths in China (3,245) by confirmed cases (80,928).

However, Professor Wu and colleagues said their estimated death rate is still 'concerning'.

The probability of dying from COVID-19 after developing symptoms was 1.4 per cent, as low as 0.8 per cent and as high as two per cent, the study in China found. Pictured, workers stand next to coffins and remains of the coronavirus victims, in Bergamo, Italy, 18 March

Professor Wu and colleagues also believe in the worst case scenario, the ‘majority the population will be infected eventually'. Pictured, workers stand next to coffins and remains of the coronavirus victims, in Bergamo, Italy, 18 March

99% OF DEATHS ARE IN THOSE WITH A PRE-EXISTING HEALTH CONDITION 99 per cent of coronavirus deaths in Italy are patients with existing medical problems, a study by the country's health service has found. Research into 355 deaths found that only three of the victims, 0.8 per cent, had been clear of illnesses before they were infected. Nearly half of them - 48.5 per cent - already had three or even more health conditions before they were diagnosed with Covid-19. Another 25.6 per cent had two other 'pathologies', while 25.1 per cent had one. The research by Italy's National Institute of Health is consistent with previous findings that people with existing illnesses are more likely to die from coronavirus. According to the study, the most common of these problems in Italy include high blood pressure, heart disease and diabetes. Some 76.1 per cent of the patients who died of Covid-19 had previously had problems with high arterial blood pressure, the study found. More than a third - 35.5 per cent - had diabetes, while 33.0 per cent had suffered from ischemic heart disease. Nearly a quarter, 24.5 per cent, had suffered from atrial fibrillation. Less common examples included dementia and liver disease. Scientists have not yet established why people with high blood pressure are more vulnerable to the coronavirus. The Centers for Disease Control and Prevention in the U.S. says it needs 'more data to become available' to investigate the link properly. Advertisement

'For the general public, the overriding concern about uncertainty can breed fear, even panic,' the study authors wrote.

'There is arguably no greater cause of such anxiety than the relative probability of death and disability caused by infection.

'While our estimates of symptomatic case fatality risk are concerning, these could be reduced if effective antivirals were identified and widely adopted for treatment of severe cases.'

Outcomes are likely to be better still with measures to 'flatten the curve' of the epidemic. This involves slowing the spread of cases by suppressing the peak.

The strategy, adopted by the British Government, has the goal of reducing pressure on health services and bides time to find treatments and vaccines.

Professor Wu and colleagues also believe that in the worst case scenario, the 'majority of the population will be infected eventually'.

This is based on the fact the virus has never been seen before, meaning no one has immunity to it, and there is currently no vaccine against it.

Unless, they say, drastic public health interventions are applied over prolonged periods 'and/or vaccines become available sufficiently quickly’.

More realistically, they envision ‘at least a quarter to a half’ will be infected.

But extreme measures, such as closing schools, pubs and restaurants, cancelling sport events and urging social distancing, have been implemented globally following the lead of China.

Wuhan has been sealed off from the outside world since late January, when all citizens were put under a state-imposed lockdown.

Scientists have been scrambling to understand how the never-seen-before coronavirus behaves since it emerged just three months ago.

The authors of this study wrote: ‘The number of severe outcomes or deaths in the population is most strongly dependent on how ill an infected person is likely to become, and this question should be the focus of attention.’

The research team also claim that adults aged between 45 to 65 are three times more susceptible to infection than those aged between 15 and 44 years.

This jumps to 6.4 times in anyone over the age of 64.

But, if their research in Wuahn is anything to go by, only 0.3 per cent of cases will actually be officially recorded due to testing restrictions and asympomatic cases.

The team published the paper in Nature Medicine on March 13, and it has not been peer-reviewed by other academics yet.

Robin May, a professor of iInfectious disease at University of Birmingham, said: 'This is a detailed epidemiological analysis and the results are cautiously encouraging, in that they indicate a lower fatality rate from COVID-19 than has thus far been estimated.

'This is a very important new piece of data that will help guide the public health response to this pandemic.

'One important caveat, though, is that this study is based primarily on data from Wuhan and therefore does not necessarily reflect mortality rates that may be seen in other areas of the world.'

The researchers noted, 'our modelled estimates have necessarily relied on numerous strong assumptions' - a variety of data sources were used which each have their own caveats.

The study was undertaken in early February, from which time the WHO has declared a global pandemic and countries have become shut off from one another.

Since then, Wuhan has turned a corner. Hopes were raised when the city reported no new cases for the first time, suggesting its strategies to contain the outbreak may have been successful.

Meanwhile, the virus continues to ravage Europe, the Americas and the rest of the world.