By Kate Kelland
LONDON (Reuters) - Britain on Tuesday announced an easing of social distancing rules from July 4, reducing the recommended gap from 2 metres to "1 metre plus" in England as it further loosened lockdown measures meant to curb the COVID-19 pandemic.
WHAT DO SCIENTISTS SAY?
Infectious disease experts say the closer people are to someone infected with COVID-19, and the more time people spend in close quarters, the higher the risk that the coronavirus will spread from one person to another.
Beyond that simple reality, "it is just a matter of reducing risk with increased physical distance", said Jonathan Reid, a professor of Physical Chemistry at Britain's Bristol University.
"The further you stand away from someone, the fewer droplets you will be exposed to. One metre only prevents you from being exposed to the largest of droplets; two metres reduces your exposure - but doesn’t make it zero risk."
A study in The Lancet this month found that physical distancing of at least 1m lowers risk of COVID-19 transmission, but that 2m could be more effective.
WHAT IS THE WORLD HEALTH ORGANIZATION'S ADVICE?
The WHO says keeping a distance of at least one metre helps reduce the risk of the coronavirus spreading in the small liquid droplets that people spray out when they cough, sneeze and talk.
These droplets may contain the virus, and "if you are too close, you can breathe in the droplets", the WHO says.
IS DISTANCE THE ONLY FACTOR?
Switzerland's health ministry says that "according to current data, a distance of more than one meter reduces the risk of COVID-19 infection by more than 80% in both healthcare (settings) and everyday life".
It added, however, that the risk is higher "in circumstances in which a particularly large number of droplets are expelled, such as when singing or speaking loudly".
Shaun Fitzgerald, a professor of engineering at Britain's University of Cambridge, said the key point is that "it's not all about the distance".
"There are other mitigation measures," he said - including the duration of close proximity, the number of people in a given space, the use of face masks, availability of ventilation, and whether people talk quietly or shout loudly.
WHAT DO OTHER COUNTRIES RECOMMEND?
China, Denmark, France, Hong Kong and Singapore recommend social distancing of 1 metre, and many people also choose to, or are required to, wear face masks in public spaces.
Australia, Belgium, Greece, Germany, Italy, Spain and Portugal advise people to keep 1.5m apart. Switzerland this week also reduced the required distance to 1.5m from 2m.
The guidance in the United States is six feet, or 1.8m.
(Additional reporting by John Miller in Zurich, editing by Mark Heinrich)