From a scientific viewpoint, this is what we do know about coronavirus

Scientists around the world have been working around the clock to learn more about Covid-19, which has caused a global pandemic. Here is what we know now about it.

Transmission

Covid-19, of the coronavirus family, made a jump from animals to humans in November or December, possibly via a pangolin in Wuhan market.

It is thought to spread mainly via people in close contact. It is spread by droplets from coughs and sneezes, contaminating the air at distances of between 6.5ft (2m) and 19.6ft (6m).

One single droplet can be enough to carry an infectious dose.

The US National Institute of Allergy and Infectious Diseases (NIAID) suggests the disease can survive in the air for about three hours and on some surfaces for as long as three days. It can live for up to four hours on copper, 24 hours on cardboard and two to three days on plastic and stainless steel.

Scientists in Singapore found the disease could spread in offices via the air conditioning or even on a draught.

China’s Hunan Provincial Centre for Diseases Control and Prevention reported an infected man passed it to nine other people on a bus. One victim had got on the bus half an hour after the infected man had alighted.

Who is most at risk?

Coronavirus is more deadly for men than women, with males 65 per cent more likely to die from an infection.

Figures from the World Health Organisation show 1.7 per cent of women who catch it will die, compared with 2.8 per cent of men.

Some experts think the imbalance relates to a higher prevalence of smoking or alcohol use among men, while others think men are more likely to have underlying conditions such as heart disease and diabetes, which make them more vulnerable.

A study in The Lancet this week showed 30 per cent of patients taken to hospital in the first outbreak in China suffered high blood pressure and 19 per cent were diabetic, both believed to be major risk factors.

Death rate

Although the overall global death rate is still being calculated, with estimates ranging from one to 3.8 per cent, the risk of death jumps to 10.5 per cent for people with cardiovascular disease, 7.3 per cent for diabetics, 6.3 per cent for those with chronic respiratory disease, 6 per cent for people with high blood pressure and 5.6 per cent among cancer sufferers.

While the chance of dying from the virus for anyone under 50 is less than 0.5 per cent, it jumps to 1.3 per cent after 50, and 3.6 per cent after 60.

But after the age of 70, the risk of death hits 8 per cent, rising to 14.8 per cent among the over-80s. There have been no deaths among children aged under 10. Fatalities among those aged 10 to 40 is 0.2 per cent.

The Government chief medical officer expects the UK death rate to be one per cent. The Government hopes 60 per cent of people catch the virus, to provide herd immunity and protect the most vulnerable. That means around 390,000 people will die.

In a bad flu year, around 13,000 people die, making coronavirus approximately 30 times more deadly.

Symptoms

The main symptoms of Covid-19 are a persistent cough, a high temperature and shortness of breath. People may also generally feel unwell, have the shakes, muscle aches or malaise. Symptoms appear four to five days after infection and peak for two or three days before lessening at day seven or eight. Most who catch it will have a mild infection but start to feel better within a week. Some people will catch it and never show symptoms.

Progression

Researchers in China studied 191 patients in Jinyintan and Wuhan Pulmonary hospitals after Dec 29, who were discharged or dead by Jan 31. They found the median time to discharge was 22 days, while the average time to death was 18.5 days.

The average duration of fever was about 12 days in survivors, which was similar in non-survivors, but nearly half still had a cough on discharge. Breathing improved around 13 days for those who recovered. For those who died, sepsis kicked in around day nine, while acute kidney or heart injury occurred by day 15. It was also found that surviving patients stayed infectious for up to 37 days.

Seasonality

Maryland university researchers found the worst cases were recorded in areas lying between 30 and 50 degrees of latitude, which share similar climate conditions, such as northern Italy, the Pacific Northwest, Japan, Iran, South Korea, France, Spain and Germany.

Areas expected to be hardest hit through geographical proximity or travel connections, such as southeast Asia, have suffered nothing like the same number of infections. Britain is at the centre of a coronavirus danger zone. If temperatures and humidity follow a similar pattern to 2019, our climate will make it a perfect breeding ground for the virus until May.

Weather records in the worst-hit areas show temperatures of between 5C (41F) and 11C (52F) and humidity of 47-79 per cent – similar to laboratory conditions in which the virus thrived.

As it gets warmer, it could die out or flourish in the southern hemisphere. In the northern hemisphere, flu season begins in October and peaks between December and February, though some cases can last until May.

Flu survives better in cold weather because it has a fatty protective coating which degrades when warm.

The Met Office three-month forecast said chances of average temperatures falling into the warmest categories was about 55 per cent while there was a five per cent chance of severe cold.

Global effect

Data from the first wave of 45,000 infections in Wuhan, showed 80.9 per cent of patients had mild symptoms, 13.8 per cent required hospital treatment and for severe symptoms, and 4.7 per cent needed intensive care.

Although Covid-19 has spread to 116 countries, the vast majority of cases have been confirmed in Wuhan, the capital of Hubei province in China, where the pandemic originated.

Taken with the 110,000 cases in Italy, Iran and South Korea, this accounts for 87 per cent of cases.

The Government believes Britain is four weeks behind Italy and expects the virus to peak in 10 to 14 weeks, toward the end of May and June.

Containment measures

Northeastern university in Boston found that travel restrictions in China delayed the spread by just three to five days. Modelling by Southampton university showed other measures, such as early detection and contact reduction, was much more effective.

Travel restrictions which began on mainland China on Jan 23 initially reduced the export of cases by about 77 per cent, but it picked up again in subsequent weeks. The Southampton study also found the lifting of intercity travel restrictions since Feb 17, which aimed to minimise economic impact, had not led to a new increase.