The health minister Edward Argar appears to have rowed back on claims by the education secretary, Gavin Williamson, that research shows a return to full-time schooling carries few risks.

Ahead of the return of pupils to schools in England in September, Argar warned that a Public Health England study into the spread of coronavirus in schools was still a work in progress. Only two days ago, Williamson said the study makes it clear there is little evidence that the virus is transmitted at school.

The research has yet to be published, and reports on Tuesday said it shows that while there is little Covid-19 spread among primary-age pupils, transmission for older students could be much the same as for adults.

Asked about this, Argar told Sky News: I think we should be cautious about reading too much into that work in progress; its important work but it isnt complete yet.

He added: On the basis of the work that has been completed and those international comparators, we are confident that children and young people are much less at risk from this disease and from passing it on than other adults more broadly in the community.

On the basis of the evidence we have thus far, we believe that the levels of transmission between young people and the infectiousness is low. In terms of schools and the approach to getting pupils back in schools.

The Covid-19 pandemic is currently unfolding in one big wave with no evidence that it follows seasonal variations common to influenza and other coronaviruses, such as the common cold, theWorld Health Organizationhas warned.

Epidemics of infectious diseases behave in different ways but the1918 influenza pandemicthat killed more than 50 million people is regarded as a key example of a pandemic that occurred in multiple waves, with the latter more severe than the first. It has been replicated albeit more mildly in subsequent flu pandemics. Until now that had been what was expected from Covid-19.

How and why multiple-wave outbreaks occur, and how subsequent waves of infection can be prevented, has become a staple of epidemiological modelling studies and pandemic preparation, which have looked at everything from social behaviour and health policy to vaccination and the buildup of community immunity, also known as herd immunity.

Is there evidence of coronavirus coming back in a second wave?

This is being watched very carefully. Without a vaccine, and with no widespread immunity to the new disease, one alarm is being sounded by the experience of Singapore, which has seen a suddenresurgence in infectionsdespite being lauded for its early handling of the outbreak.

Although Singapore instituted a strong contact tracing system for its general population, the disease re-emerged incramped dormitory accommodationused by thousands of foreign workers with inadequate hygiene facilities and shared canteens.

Singapores experience, although very specific, has demonstrated the ability of the disease to come back strongly in places where people are in close proximity and its ability to exploit any weakness in public health regimes set up to counter it.

In June 2020, Beijing suffered from a new cluster of coronavirus cases which caused authorities to re-implement restrictions that China had previously been able to lift. In the UK, the city of Leicester was unable to come out of lockdown because of the development of a new spike of coronavirus cases. Clusters also emerged in Melbourne, requiring a re-imposition of lockdown conditions.

What are experts worried about?

Conventional wisdom among scientists suggests second waves of resistant infections occur after the capacity for treatment and isolation becomes exhausted. In this case the concern is that the social and political consensus supporting lockdowns is being overtaken by public frustration and the urgent need to reopen economies.

However Linda Bauld, professor of public health at the University of Edinburgh, says Second wave isnt a term that we would use at the current time, as the virus hasnt gone away, its in our population, it has spread to 188 countries so far, and what we are seeing now is essentially localised spikes or a localised return of a large number of cases.

The overall threat declines when susceptibility of the population to the disease falls below a certain threshold or when widespread vaccination becomes available.

In general terms the ratio of susceptible and immune individuals in a population at the end of one wave determines the potential magnitude of a subsequent wave. The worry is that witha vaccine still many months away, and the real rate of infection only being guessed at, populations worldwide remain highly vulnerable to both resurgence and subsequent waves.

Peter Beaumont,Emma Graham-Harrison and Martin Belam

Downing Street is keen to stress the safety of a return to school for all pupils in England, with Boris Johnson saying it is a moral duty to ensure children do not miss out on any more formal education.

The PHE study is likely to be published in full next week, and ministers are keen to reassure parents about safety. One report on Tuesday said No 10 had asked Chris Whitty, the chief medical officer for England, to compile a review of the evidence on transmission in schools, to reassure parents and teachers.

There are not, however, any plans for routine coronavirus testing in schools, with teachers and students only being tested if they show symptoms.

In another interview on Monday, Argar said there were also no plans to ask any pupils to wear masks.

Thats not something thats in prospect at this point, he told BBC Breakfast: Weve been clear and the Department for Education have been clear that that poses a challenge to actually the ability to teach and the ability to learn in certain contexts.

We dont think that thats necessary at this point, not least because we are essentially setting up different class groups or year groups as social bubbles.

But at the moment we believe the measures that have been put in place around social distancing, around those bubbles and around the facility to test if necessary, are the right ones to continue to make our schools safe when they reopen.

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Health minister: Covid study cited by Gavin Williamson is 'work in progress' - The Guardian