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.

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.

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.

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