Schools have been warned by public health officials against “over-ventilating” classrooms to stop the spread of Covid-19 by leaving windows “open all the time”.

Hepa air filters have no role in preventing infections in classrooms, according to senior National Public Health Emergency Team officials (Nphet), who also restated their belief that current high rates of infection among schoolchildren are the result of wider trends in the community rather than in-class transmission.

A further 3,793 new cases of Covid-19 were reported in the State on Wednesday, as well as 55 newly notified deaths in the past week. This brings the total deaths in Ireland related to Covid-19 to 5,707.

Hospital Report

There were 578 patients in the country’s hospitals with the virus, of which 117 were in ICU as of 8am Wednesday morning.

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Prof Philip Nolan said Hepa filters have an application in small spaces with a known source of infection, such as hospitals. They must be placed near the source, he told a media briefing on Wednesday.

“They are not useful in the far corner of a room with 20 to 30 people, where you don’t know the source of infection. You’re better off paying attention to mitigating measures that prevent close-range transmission.”

Prof Nolan said the high incidence in 5-12 year-olds was the result of earlier high incidence in 18-30 year-olds and other adults. “We first of all see it in the older community and then we see it in children.”

Ventilation is one of effective mitigating measures in schools

He said a typical classroom is “quite big”, at least 150 cubic metres, or up to six times the size of a normal room.

Ventilation was important but it was also important not to “over-ventilate”. Carbon dioxide levels should be kept below recommended levels, which he said was 1,150 parts per million, not 800 or 600 (as asserted by critics of official policy on the issue).

The major factor driving the rise in cases among younger schoolchildren remains socialisation outside the school setting, according to deputy chief medical officer Dr Ronan Glynn.

This wasn’t surprising given this age group is not vaccinated, in a society that is almost entirely open, he said.

He said a whole range of mitigation measures should be in place in education but that didn’t mean “windows have to be kept open all the time”.

The reason Nphet had changed its position on mask-wearing for children aged nine and up was because the underlying disease profile for this age-group has “substantially changed”.

Slowed infection rate

Speaking earlier on Wednesday, Dr Holohan said there was a continuing increase in cases among young people, especially those aged five to 12 years. Testing was up in younger age groups and those aged 35-44.

Dr Holohan attributed the high number of cases in younger age groups to “increased case finding activity”.

While cases have slowed and are stable they are at a very high number, Dr Holohan said, and this leaves the country exposed to the results of a potential increase in socialisation around Christmas, as well as the uncertainty around Omicron.

Current growth rates are “close to zero” and the situation is “stable but very high risk”, Prof Nolan said. It was important to face into the winter with lower numbers of Delta cases than we have so the emphasis must be on reducing these numbers.

Prof Nolan described a steep gradient among cases in younger children, with the rate among five-year-olds close to the population average but that among 11-year-olds twice this figure.

“Things have changed. There’s clearly been some population response, marginal though it might have been, to the public health messaging.”

He said cases are tracking “somewhat better” than the optimistic model outlined at the start of November. Current models show if social contact is maintained or slightly decreased, case numbers will decline “over the coming weeks”.

New scenarios based on the Omicron variant’s potential for greater transmission or vaccine escape will be drawn up next week.

The positive impact of boosters is beginning to be seen in cases among the 70-79 year age-group, Dr Nolan said. The number of cases requiring hospitalisation is down to 15 per 1,000, from 20.