THE risk of children and teachers spreading coronavirus once schools re-open is low as long as effective contact tracing, hygiene and physical distancing is in place, according to a study from Australia.

It comes as schools in Scotland prepare to re-open fully next Tuesday.

Researchers examined transmission between January and April in New South Wales (NSW), where prevalence of the virus was low and most schools and nurseries remained open during the pandemic with reduced attendance by pupils only from the peak of the epidemic.

They identified 27 cases in 15 schools and ten nurseries where individuals had attended while infectious - defined as 24 hours prior to the onset of Covid-19 symptoms including a new cough, fever, or loss of taste or smell.

READ MORE: Teachers raise fresh concerns over return to school in Scotland

These cases only resulted in a total of 18 secondary infections, however, out of a total of 1,448 close contacts within the school or nursery environment.

Close contacts were defined as anyone who had had face to face interaction for a minimum of 15 minutes, or spent 40 minutes in an indoor space, with an infected person.

Anyone who had been potentially exposed to the virus in this way by sharing space with one of the 12 pupils and 15 adults who tested positive for Covid-19 was told to quarantine at home for 14 days. They were subsequently offered testing if they developed possible symptoms.

Five of the 18 secondary cases - three pupils and two adults - occurred in just three schools.

In nine of the 10 nurseries where a case of Covid-19 was detected, there were no secondary infections at all.

However, one nursery experienced a "large outbreak" resulting in the virus spreading to six adults and seven children - including three children under one who remained asymptomatic.

The index case was initially identified as a two-year-old, but subsequent investigation traced the primary case to a staff member.

It was unclear where they had picked up the infection, but the researchers stressed that this incident had occurred early on in the pandemic "when the criteria for testing was more narrow".

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The study covered 3,103 primary and secondary schools and 4,600 nurseries for children aged six weeks to five years old across NSW from January 25 - when Australia reported its first Covid-19 case - to April 9, when term ended. Close contact follow-up was extended to May 1.

Schools and nurseries remained open for most of the term, with physical distancing and enhanced cleaning and hygiene measures in place.

After March 22, when the epidemic peaked, children were encouraged to stay home until term ended with online 'distance learning' implemented.

Schools remained open for pupils for whom home schooling was not an option, but the researchers note that this resulted in a drop in school attendance from 90 per cent to approximately 5%.

The authors conclude: "Sars-CoV-2 transmission rates were low in NSW educational settings during the first Covid-19 epidemic wave, consistent with mild infrequent disease in the 1·8 million child [under-18] population.

"With effective case-contact testing and epidemic management strategies and associated small numbers of attendances while infected, children and teachers did not contribute significantly to Covid-19 transmission via attendance in educational settings."

READ MORE: Scotland records third highest rate of excess deaths in Europe during pandemic

The study was led by Professor Kristine Macartney, a paediatrician specialising in infectious diseases and vaccinology at Sydney University and director of Australia's National Centre for Immunisation Research and Surveillance.

She said: “The study adds valuable data, but it is important to view these findings in the context of the NSW outbreak.

"It may be that higher rates of transmission occur in areas with higher levels of infection and where contact tracing and public health measures were not as rigorous as in Australia, where borders were closed and quarantine measures were strongly enforced.

"Schools were also closed temporarily for thorough cleaning if a pupil or staff member was found to be infected.”

It comes as modelling by the researchers at UCL and the London School of Hygiene and Tropical Medicine predicted that a second wave of Covid would peak in in the UK in December if levels of contact tracing and diagnoses fall below necessary thresholds after schools in England and Wales return in September.

Their modelling suggests a second wave might be avoided with increased testing.

This should mean that between 59% and 87% people showing symptoms are tested at some point during active infection, with effective contact tracing and isolation also in place.

The scenario is based on schools returning full-time in September and other lockdown measures having been eased, including more adults returning to work.

If levels of diagnoses and contact tracing fall below this benchmark, a second wave would peak in December.

If a part-time rota system were adopted for pupils returning to school in September, the second peak in Covid cases would be delayed until February.

Dr Jasmina Panovska-Griffiths, who lead the study, said: “Our modelling suggests that with a highly effective test and trace strategy in place across the UK, it is possible for schools to reopen safely in September.

"However, without sufficient coverage of a test-trace-isolate strategy the UK risks a serious second epidemic peak either in December or February.

"Therefore, we urge the government to ensure that test-trace-isolate capacity is scaled up to a sufficient level before schools reopen.”

Both studies are published today in the journal Lancet Child & Adolescent Health.