By David Shukman Science editor
With the risk of catching coronavirus indoors well established, the little allowed contact with friends under lockdown is for outdoor exercise.
But what are the risks when you go for a walk with a friend? And can you catch coronavirus from a jogger, or people sheltering at a bus stop to escape the rain?
Researchers say infections can happen outdoors, but the chances are massively reduced.
Fresh air disperses and dilutes the virus.
It also helps to evaporate the liquid droplets in which it is carried.
On top of that, ultraviolet light from the Sun should kill any virus that’s out in the open.
Even so, there are a handful of cases where it’s believed that infections did happen outside.
One study found that two men in China talking face-to-face for at least 15 minutes was enough to spread the virus.
So the risks are low but not zero, but what are they?
If someone’s infected – maybe without realising it because they have no symptoms – they’ll be releasing the virus as they breathe, especially if they cough.
Some of that will be carried in droplets, most of which will quickly fall to the ground but could reach your eyes, nose or mouth if you’re within 2m (6ft) of them.
So the advice is to avoid being face-to-face if you’re that close.
The infected person will also release smaller particles called aerosols.
Indoors, these can accumulate in the air and be a hazard, outside they should rapidly disperse.
Walking past someone in the street or having a jogger run by you, means you’re close together for a few seconds at most.
Fleeting encounters are highly unlikely to be long enough for enough virus to reach you.
“We don’t want people to be terrified of passing each other in the street,” says Prof Cath Noakes, a government adviser speaking in a personal capacity.
She says someone would have to cough right at you, and for you to inhale at just the wrong moment, for an infection to happen.
But she also warns of friends spending a long time together outdoors and assuming they’re completely safe.
Going for a run with someone and following close behind them for 20 minutes or more, breathing in their slipstream, might be a problem, she says.
“The sad fact is that your greatest risk is from the people you know.”
Scientists have found that the risks are low in fully open spaces.
But they worry about areas that are not just crowded but also partly enclosed, such as market stalls or bus shelters.
Whenever the air is still, it can become stagnant and contaminated.
It’s in environments like narrow pathways or busy queues that government advisers say face coverings may be needed.
If an infected person coughs into their hand and then wipes it on a surface, the virus may survive there for hours.
Researchers in the US found virus on the handles of rubbish bins and the buttons at pedestrian crossings.
They reckon this may have led to infections in the area, though at a relatively low level compared with other ways of spreading the virus.
But in the winter, the virus may last longer in the open.
It thrives in low temperatures – it may be one reason why there have been outbreaks in chilly meat-processing plants.
Added to that, it’s the season when your nose runs in the cold, and a common reaction is to wipe it with your hand.
That might raise the chances of surfaces becoming contaminated.
However, many scientists now think that the amount of virus likely to be left on a surface in this way would be minimal, and would disperse within an hour or two.
“The chance of transmission through inanimate surfaces is very small,” says Prof Emmanuel Goldman of Rutgers University.
All the evidence points to the vast majority of Covid infections happening indoors.
The virus is transmitted through human interaction, especially when people are together for a long period of time.
That means the virus can spread in several different ways.
Either infected droplets can land on people close by, or contaminate surfaces that others touch.
And if rooms are stuffy, tiny virus particles can accumulate in the air and get inhaled.
It’s in households where all of this is most likely to happen.
A medical test that can show if a person has had the coronavirus and now has some immunity. The test detects antibodies in the blood, which are produced by the body to fight off the disease.
Someone who has a disease but does not have any of the symptoms it causes. Some studies suggest some people with coronavirus carry the disease but don’t show the common symptoms, such as a persistent cough or high temperature.
The first part of the UK’s strategy to deal with the coronavirus, which involved trying to identify infected people early and trace anyone who had been in close contact with them.
One of a group of viruses that can cause severe or mild illness in humans and animals. The coronavirus currently sweeping the world causes the disease Covid-19. The common cold and influenza (flu) are other types of coronaviruses.
The disease caused by the coronavirus first detected in Wuhan, China, in late 2019. It primarily affects the lungs.
The second part of the UK’s strategy to deal with the coronavirus, in which measures such as social distancing are used to delay its spread.
Fixed penalty notice
A fine designed to deal with an offence on the spot, instead of in court. These are often for driving offences, but now also cover anti-social behaviour and breaches of the coronavirus lockdown.
Flatten the curve
Health experts use a line on a chart to show numbers of new coronavirus cases. If a lot of people get the virus in a short period of time, the line might rise sharply and look a bit like a mountain. However, taking measures to reduce infections can spread cases out over a longer period and means the “curve” is flatter. This makes it easier for health systems to cope.
Short for influenza, a virus that routinely causes disease in humans and animals, in seasonal epidemics.
Supports firms hit by coronavirus by temporarily helping pay the wages of some staff. It allows employees to remain on the payroll, even though they aren’t working.
How the spread of a disease slows after a sufficiently large proportion of a population has been exposed to it.
A person whose body can withstand or fend off a disease is said to be immune to it. Once a person has recovered from the disease caused by the coronavirus, Covid-19, for example, it is thought they cannot catch it again for a certain period of time.
The period of time between catching a disease and starting to display symptoms.
Hospital wards which treat patients who are very ill. They are run by specially-trained healthcare staff and contain specialist equipment.
Restrictions on movement or daily life, where public buildings are closed and people told to stay at home. Lockdowns have been imposed in several countries as part of drastic efforts to control the spread of the coronavirus.
The third part of the UK’s strategy to deal with the coronavirus, which will involve attempts to lessen the impact of a high number of cases on public services. This could mean the NHS halting all non-critical care and police responding to major crimes and emergencies only.
The NHS’s 24-hour phone and online service, which offers medical advice to anyone who needs it. People in England and Wales are advised to ring the service if they are worried about their symptoms. In Scotland, they should check NHS inform, then ring their GP in office hours or 111 out of hours. In Northern Ireland, they should call their GP.
Multiple cases of a disease occurring rapidly, in a cluster or different locations.
An epidemic of serious disease spreading rapidly in many countries simultaneously.
This is when the UK will start to lift some of its lockdown rules while still trying to reduce the spread of coronavirus.
PPE, or personal protective equipment, is clothing and kit such as masks, aprons, gloves and goggles used by medical staff, care workers and others to protect themselves against infection from coronavirus patients and other people who might be carrying the disease.
The isolation of people exposed to a contagious disease to prevent its spread.
R0, pronounced “R-naught”, is the average number of people who will catch the disease from a single infected person. If the R0 of coronavirus in a particular population is 2, then on average each case will create two more new cases. The value therefore gives an indication of how much the infection could spread.
This happens when there is a significant drop in income, jobs and sales in a country for two consecutive three-month periods.
Severe acute respiratory syndrome, a type of coronavirus that emerged in Asia in 2003.
Staying inside and avoiding all contact with other people, with the aim of preventing the spread of a disease.
Keeping away from other people, with the aim of slowing down transmission of a disease. The government advises not seeing friends or relatives other than those you live with, working from home where possible and avoiding public transport.
State of emergency
Measures taken by a government to restrict daily life while it deals with a crisis. This can involve closing schools and workplaces, restricting the movement of people and even deploying the armed forces to support the regular emergency services.
These can be used by government ministers to implement new laws or regulations, or change existing laws. They are an easier alternative to passing a full Act of Parliament.