A new study has suggested that the compulsory use of face masks can slow the spread of Covid-19 cases by as much as 40%.

The German report, published as a discussion paper for the Institute of Labour Economics, determined that mandatory face masks can "reduce the daily growth rate of reported infections by around 40%".

The study involved researchers examining the growth rate of cases in regions across Germany in the days following the introduction of masks in shops and on public transport.

For the experiment, the team of scientists from Johannes Gutenberg University Mainz and the University of Southern Denmark closely studied the German city of Jena, which introduced mandatory face masks on 6 April.

The number of positive coronavirus cases recorded in the city fell by 25% over the next 20 days.

The report said: "Comparing the daily growth rate in the synthetic control group with the observed daily growth rate in Jena, the latter shrinks by around 60% due to the introduction of face masks.

"This is a sizeable effect. Wearing face masks apparently helped considerably in reducing the spread of Covid-19."

In Ireland, people are being recommended to wear face coverings on public transport, in shops or situations where it is difficult to maintain social distance.

Yesterday, Chief Medical Officer Dr Tony Holohan said the National Public Health Emergency Team had "no change" regarding advice on face coverings in Ireland.

He said efforts need to be redoubled toward ensuring people wear face coverings in enclosed spaces, adding there is concern that there is a belief a face covering removes the need for other measures.

"The advice remains to wear them on public transport and in enclosed settings such as retail outlets. We do think the message needs to be re-enforced. The level of compliance is not where it needs to be."

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From next week people using public transport in England must wear face coverings under government rules.

While the researchers behind the German study hailed the results, they said more detailed analysis is still required before any definitive conclusion on the effectiveness of face masks can be made.

"Our results provide some initial empirical evidence on this important matter (but) we simultaneously stress the need for more detailed analyses," the report stated.

"First, Germany is only one country. Different norms or climatic conditions might change the picture for other countries.

"Second, we have ignored spatial dependencies in the epidemic diffusion of Covid-19. This might play a role.

"Third, there are various types of face masks. We cannot identify differential effects since mask regulations in German regions do not require a certain type.

"This calls for further systematic causal analyses of the different health measures implemented to fight the spread of Covid-19." 

Around 80% of cases of Covid-19 will be a mild to moderate illness, close to 14% have severe disease and around 6% are critical.

Generally, you need to be 15 minutes or more in the vicinity of an infected person and within 2 metres of them, to be considered at-risk, or a close contact.