Last month, a Stop Covid-19 Hanging Around publicity campaign launched in the United Kingdom, following research that showed only a third of the public there understood the importance of ventilation.

"People with Covid-19 release virus particles into the air whenever they speak, breathe or cough and these can linger in unventilated settings," said Thomas Waite, deputy chief medical officer for England.

“It’s vital everyone understands the importance of using ventilation, such as regularly opening windows – even if just for a few minutes – to keep the air moving and prevent infections,” said Dr Waite.

Hospital Report

There has been expert advice on the need for better air ventilation in Ireland to combat the spread of the virus,too. But the message has been slower to get through.

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Earlier this year, the Health Information and Quality Authority said inadequately ventilated indoor spaces presented a risk of transmission with super-spreading potential.

Presented with the image of freezing schoolchildren huddled in classrooms during a recent radio interview, Minister for Health Stephen Donnelly, however, said expert advice on Hepa air filters is that they "are not required".

Hepa filters sieve out Covid-19 and other viruses from the air and have been recommended for places such as classrooms, where even open windows may not be sufficient to protect the numbers of children inside.

At relatively low cost, some experts say they are a good idea, while others disagree. But there are hopes they would allow teachers to close some windows during the worst of the colder months to come.

With winter weather deteriorating, the filters – like face masks and antigen tests before them – have become the latest division in the war of opinion on how best to fight an intractable pandemic that has left the public exhausted.

A greater emphasis on air quality in places such as Japan has meant there are now fewer cases "in Tokyo than there are in Rathfarnham", complains Prof John Wenger from UCC's School of Chemistry and Environmental Research Institute.

Raising awareness

Groaning at the mere mention of Hepa filters and the lack of Government support for them, Wenger says “virtually nothing” was done here until last May to raise awareness among the public about the need for better ventilation.

That has slowly changed since, he says, singling out the Health and Safety Authority and the Department of Education: "Only now in the last month or two have we had the leading figures [in the public health response] . . . actually saying ventilation" is important, he says.

“It’s all a bit too late. They need stronger messaging to counteract what has already set in, in terms of the general public’s response,” says Wenger, who chaired the Role of Ventilation in Reducing Transmission of Covid-19 expert groups.

Established as a subgroup of the National Public Health Emergency Team (not the HSE group that advised the Minister), it recommended the use of Hepa filters, particularly in areas that are difficult to ventilate, including some crowded classrooms.

“They are extremely efficient at removing respiratory particles from the air and they can be like a temporary drop-in solution to clean the air,” says Prof Wenger.

“So you get a combination of the natural ventilation . . . plus the Hepa removing the particles from the air. I don’t understand why they [the Government] didn’t take our advice. We have scoured the literature and all available guidance. You look at any guidance in the world on this and poorly ventilated areas would benefit from the use of Hepa filters,” he adds

When an infected person speaks, coughs or sneezes, the virus is released in respiratory particles known as droplets. Smaller drops, aerosols, are invisible and can hang in the air for hours, particularly in poorly ventilated spaces.

The cigarette smoke analogy is popular, says Wenger. In a stuffy room, smoke lingers long after it has been exhaled. Over time, depending on ventilation levels, the amount of virus can increase or reduce.

The early days of the pandemic were marked by public health messaging centred on the need to avoid larger droplets with limited range, using social distancing and hand washing rules: “In reality the vast majority of the [infected] particles are way smaller than those,” says Prof Wenger.

Like pollen or dust, they drift in the air. That means the virus could also spread like measles or tuberculosis, airborne diseases, as opposed to typical respiratory infections. Still, there are some unknowns, including how long the disease can survive in aerosol form.

‘Transmission interventions’

Asst Prof Kim Roberts at the of School of Genetics and Microbiology in Trinity College Dublin, a member of the expert group, hopes that with Christmas approaching and the temptation to gather indoors, public awareness will be heightened.

“The [State] chief medical officer [Tony Holohan] is talking about it more. We’ve got people in Government mentioning ventilation when they’re talking about the transmission interventions. I hope that we are going to see a change in understanding,” she says.

Carbon dioxide monitors help – small, portable and relatively inexpensive – guide people on how clean the air is in a given space at any time by monitoring the levels of CO2 exhaled by people in it. Stale air can be flushed out by opening windows and doors.

“We’re planning for Christmas, we’re thinking ahead, we’re wanting multigenerational gatherings to take place. I do think we can do that, but we do need to think it through,” says Prof Roberts.

Monitors work on a system of parts per million (ppm) – 400ppm is typical outside air quality; 800ppm is safe indoor quality. Anything above about 1,000ppm requires action, such as opening a couple of windows to create through flow.

Marie Coggins, another expert group member and senior lecturer in exposure science at the School of Physics at NUI Galway, worries that many businesses are unable to ensure ventilation systems and CO2 monitors are used correctly, and they need help.

“I would be worried about smaller businesses from now until Christmas. This is their busiest period, they want to keep open but you rarely see a CO2 monitor. Do they understand their ventilation system?” asks Dr Coggins.

“Larger organisations have been doing this for years anyway. They have the environmental health and safety expertise in their team. But it’s the smaller groups I worry about that don’t,” she adds.

Restaurant Association of Ireland chief executive Adrian Cummins says his members have not been told to install CO2 monitors or filters and were denied State grants for them when they asked earlier this year. "Nobody knows what level you should be looking for," he says.

However, businesses are increasingly aware that customers will decide on where to go to eat and drink on where they think they can do so safely, as illustrated by the Saba restaurants in Dublin and Kildare that have invested in CO2 monitors and complex air-disinfection systems.

"The science is proven; the physics is proven. Our customers love to see it," owner Paul Cadden told The Irish Times this week. "People are much more conscious of it . . . they are aware that this is an airborne disease."