Imposing lockdown restrictions earlier has been linked to greater reductions in new coronavirus cases, a study has found.

The research, published in the BMJ on Wednesday, also found that physical distancing measures, such as closing schools, workplaces and public transport, and restricting mass gatherings, were associated with a “meaningful reduction” in new Covid-19 cases.

Based on data gathered from 149 countries and regions, the study found that on average the implementation of any physical distancing measure was associated with an overall reduction in Covid-19 incidence of 13%.

A team of UK and US researchers compared the change in new cases of Covid-19 before and up to 30 days after implementation of physical distancing measures in the early stages of the pandemic.

Their findings are based on daily reported cases of Covid-19 for 149 countries or regions that implemented one or more of five physical distancing measures between January 1 and May 30.

These were closing schools, workplaces and public transport, restrictions on mass gatherings and public events, and lockdown restrictions on people’s movement.

They found that, in combination with school and workplace closures, restriction on mass gatherings seemed to be “a key component” associated with a decrease in new Covid-19 cases.

However, closure of public transport was not associated with any additional reduction in incidence when the other four physical distancing measures were in place, they added.

Researchers said the data also showed that earlier implementation of lockdown, together with other physical distancing measures, was associated with a larger reduction in the incidence of Covid-19.

They said that the findings should help inform policy decisions as countries prepare to impose or lift lockdown restrictions.

The study added: “Physical distancing interventions were associated with reductions in the incidence of Covid-19 globally.

“No evidence was found of an additional effect of public transport closure when the other four physical distancing measures were in place.

“Earlier implementation of lockdown was associated with a larger reduction in the incidence of Covid-19.

“These findings might support policy decisions as countries prepare to impose or lift physical distancing measures in current or future epidemic waves.”

The researchers also found that on average physical distancing measures were first implemented nine days after the first reported case in a country.

However, they said that some countries took longer to implement measures, including Thailand at 58 days, Sri Lanka and the UK both at 45 days, and Cambodia, Sweden and the USA at 40 days.

But the researchers said that the study was limited in its ability to “establish cause” as well as being unable to assess compliance with physical distancing or the use of other measures which might reduce transmission such as face coverings or contact tracing apps.