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What does the data we have tell us about Covid-19 outbreaks in this school year?

A shift in how Covid-19 cases in schools are being dealt with has taken place this week – so how bad is transmission?

Image: Shutterstock/Halfpoint

THERE HAS BEEN a shift this week in how Covid-19 cases in schools are being dealt with by school management and public-heath authorities.

On Tuesday, The Journal reported that the HSE had recommended that principals can inform parents when there has been a confirmed Covid-19 case in their child’s school, as long as they have parental permission and are GDPR compliant. This contradicts previous guidance issued to schools in September when contact tracing ended.

On Wednesday, Minister for Health Stephen Donnelly said that antigen tests would be used in schools for ‘targeted’ contact tracing when there is a confirmed case.

On Thursday, the details of how that would work were announced by Minister for Education Norma Foley: antigen tests will be used to test the pod of a child who is confirmed to have Covid-19, and the whole class if there are more than two PCR-positive cases.

All these changes come amid concern from parents and teachers that the schools have been “left in the dark” about Covid-19 and its spread since contact tracing ended.

Analysis of the data available indicates that the testing positivity rate of Covid-19 among children under the age of 12 peaked before the schools opened at the end of August, and that the education sector is one of the workplaces with the lowest incidence rates of Covid-19 currently. 

But there are more children with Covid-19 than there had been during the summer months, due to an overall increase in Covid-19 cases in the community. This has increased demand for a version of contact tracing to return – it is hoped that the new antigen testing system will provide this safety net.

Here’s what we know about how Covid is behaving in school settings, based on weekly data published by the Health Protection Surveillance Centre (HPSC) and HSE.

This piece will include a look at Covid-19 incidence rates among children, but an increase in under-18-year-olds alone is not enough to tell whether they became infected in a school setting.

How likely is Covid-19 transmission in schools?

Over the course of the pandemic, if we look at how many Covid-19 cases there have been among children, in comparison to cases overall, it’s clear that huge spikes in adult Covid-19 cases translates into the most significant increases in Covid-19 cases among children.

Before and after schools reopen, there isn’t the same huge spike in cases.

Since the beginning of the fourth wave on 27 June, there have been 1,543 confirmed cases linked to school settings, with seven hospitalisations in that same time period and no ICU admissions or deaths.

Of a total of 4,284 outbreaks across all settings in the fourth wave, 343 outbreaks were in schools, representing 10.4%. This proportion of the total is less than private households (25%) and workplaces (12.9%), but more than hospitals (4.6%) and retail (4.6%).

The latest analysis of sectors of employment shows that education is among the four sectors with the lowest 7-day and 14-day Covid-19 incidence rates. The sectors with incidence rates below education are agriculture, IT, and transportation & storage.

Education Source: Gov.ie

Positivity rate

Covid-19 test data among children aged 0-4 and 5-12 also shows that the positivity rate began increasing during July to a peak of almost 10% and over 15% in mid-August, before schools opened.

This followed on from a dramatic increase in positivity rates among both 13-18 year olds and 19-to 24-year-olds a few weeks previous.

In mid July, during the school summer holidays, HSE chief Paul Reid said that a third of all Covid-19 cases were among children aged under 13. At that point, there were around 1,000 cases of Covid-19 a day, and the incidence rate was around 274 cases per 100,000. The volume of children testing positive is now higher, however.

When schools opened at the end of the month, that positivity rate dramatically dropped off for both age groups. Positivity increased among all age groups from the end of September.

Test positivity Source: Gov.ie

The difference vaccination makes

Week 35, beginning the 29 August, marks the start of the academic year for most students. 

All cases Source: HPSC (week 45 data)

In week 30, beginning 25 July, Covid-19 vaccines began to be offered to those aged under 18 years; the HPSC notes that a downturn in disease incidence in this cohort was observed after that until recent weeks.

Week 32, beginning the 8 August, is when the rollout of Covid-19 vaccines to 12- to 15-year-olds began – there is a notable drop off in cases among that cohort in the weeks that followed. 

Children age group Source: HPSC (week 45 data)

Contact tracing ends and the mid-term break

Week 39, beginning 26 September, marks when contact tracing was ended in schools aged under 12 years of age. Children who were asymptomatic close contacts of confirmed cases in schools no longer had to restrict their movements.

This change was made because a high number of asymptomatic children who were close contacts of confirmed cases were missing school days while isolating, despite not developing Covid-19.

This information was based on a 5% positivity rate among close contacts of a confirmed case in a school setting in the first four weeks of the academic year, compared to a 25% positivity for household close contacts.

Week 43, beginning 24 October, marks the mid-term break. NPHET member and modelling expert Professor Philip Nolan said earlier this month that the mid-term break “forced infections” among children aged 5-12, compared to the week before where it appeared to stabilise. 

In the latest week we have data for, week 45, there were 37 confirmed cases from 16 outbreaks linked to schools. 

High incidence rates among 5-12 year olds

On 27 October, Dr Ronan Glynn said at a NPHET briefing that Covid-19 incidence rates were highest in children aged 5-12, and that it wasn’t entirely clear why this was.

The rate of infection among 5-12 year olds increased from 266.1 per 100,000 in week 35 (29 August) to 402.1 per 100,000 in week 37 (12 September).

The HPSC notes that “similar increases were observed in this age group when primary schools re-opened in September 2020 and in February/March 2021″, and” may reflect increased testing of mildly symptomatic and asymptomatic children” catching cases that would otherwise go unconfirmed.

This school year, the number of outbreaks in schools dropped in the lead up to the mid-term break (10, 2, 15, 11 and 5 outbreaks per week).

School outbreaks: how big are the numbers?

During week 45, the latest week for which data is available, running from 7-13 November, there were 16 outbreaks associated with schools; compared to just two outbreaks that occurred in the previous week (an outbreak being one or more cases of Covid-19).

In the two outbreaks from the previous week, one involved two cases, and the other involved 18 linked cases.

Three outbreaks were reported in two primary schools and one Special Educational Needs setting in week 40 (3 October) with 15 Covid-19 cases across all three outbreaks: with one case, two cases and 12 cases per each of those outbreaks.

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In the following week, there were six outbreaks in primary schools, linked to 52 cases, with a range of 2-19 cases per outbreak. 

In 32 Covid-19 outbreaks reported to authorities recently, but that had occurred in May/June of the last academic year, there were 192 cases across those outbreaks, ranging from no further linked cases to 37.

So far, 31% of the total outbreaks associated with schools involved only two linked cases.

Covid spreading between adults and children

At a NPHET briefing earlier this month, Professor Martin Cormican, Clinical Lead on Infection Control at the HSE, said children going to school was not driving the latest surge in Covid-19 cases in Ireland.

Prof Cormican said that the least likely way that Covid spreads from one person to another is for a child to give Covid-19 to an adult, and the next least likely way it spreads is for a child to transmit it to another child.

The next least likely mode of transmission is for an adult to give it to a child, and the most likely way of transmission is for an adult to give it to another adult, he said.

Communication with parents 

University of Limerick Professor Orla Muldoon, who is a member of NPHET’s communication advisory group, told RTÉ Radio’s Morning Ireland that better communication was needed between the Government and parents.

Parents are being told: ‘Well, don’t have a party’, but their children are being sent in to a school where there are 30 children. That doesn’t make sense to the average parent. How is it that the party is a problem but the school isn’t?

“The other thing about making it make sense is that we need to be sure that the advice that people are getting is consistent with what we now know about Covid.

“We now know that Covid is airborne. Therefore it doesn’t make sense to ask parents to cancel outdoor parties. In fact, it makes less sense to ask them to cancel outdoor parties than to ask them to continue to send their children to school,” Professor Muldoon said.

“These kinds of contradictions make it very difficult for parents to stay with what’s messaged,” she said.

The rollout of antigen testing in schools at the end of the month may shed more light on how Covid-19 might be spreading in some school settings.

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