Action is needed now on school ventilation

We can’t allow complacency to set in as we battle Covid. Ventilation remains a major issue for schools and now is the time to act, writes Azeem Majeed

Unless the limitations of current social distancing and infection control measures in schools is properly dealt with, the prime minister’s wish to see schools reopen for good could easily be dashed by a third wave.

We understand why keeping schools open is a global priority. School closures have a major impact on the educational and social development of children, particularly those from disadvantaged backgrounds. They have economic impacts that also disproportionately affect parents in less well-paid jobs.

We are also alive to the concerns of school staff, especially those with underlying medical conditions, those who are older and those with vulnerable household members. Most may now have received their first vaccine dose, but now is not the time for complacency.

The key is ventilation. Until recently, our chief suspect as the primary means of Covid transmission has been larger virus-containing respiratory particles (droplets). These droplets generally fall to the ground within two metres of their source after a short time, so physical distancing and masks combine to reduce exposure and the risk of infection from them.

However, there is now good evidence that Covid-19 can also be transmitted through aerosols, particles smaller than droplets that remain in the air over time and distance. Traditional physical distancing measures and standard face masks are less effective in preventing the spread of infection through aerosols, but ventilation can help reduce this risk.

There is good evidence that Covid can be transmitted through aerosols

The risk of infection is substantial in poorly ventilated rooms, particularly if there are activities taking place such as singing or talking loudly. Halving the number of these small droplets in the air with no ventilation takes five minutes but with mechanical ventilation alone, that time is cut to around 1.4 minutes. In a room where a door and window are open, it falls to 30 seconds. Hence, good ventilation substantially reduces the amount of exposure for a room’s occupants and thereby reduces their risk of infection.

Increasing ventilation lowers the concentrations of any viruses that may be in the air. To achieve this and keep a comfortable ambient temperature, more modern buildings commonly use heating and ventilation systems that create a mixture of fresh and re-circulated air. Sadly, such systems are often not present in England’s schools.

As a result, most schools kept windows and doors open and the heating on for many weeks before the latest closures. If a third (or fourth) wave is likely to be with us by next autumn, then we must surely begin to plan for a better solution for pupils, teachers, school budgets and the environment. For now, every increase in air circulation helps. Switching on a fan blowing air outside when rooms are empty, for example, can help to dilute viral concentration before the next group take their seats.

But diluting concentrations of respiratory particles through circulation is second to removing them altogether from the ambient air. In more modern schools fitted with ventilation systems, it may be possible at relatively low cost to add air filtration and cleaning devices. The use of additional measures such as HEPA (high-efficiency particulate air) filters can further reduce the risk of infection. Portable HEPA filtration devices are available for schools with no existing infrastructure, but the cost (considering the number of classrooms) will be high.

In short, keeping schools open safely requires urgent action to implement more effective on-site mitigation strategies – with particular attention to ventilation. Failure to implement adequate control measures could result in Covid-19 outbreaks that – even if the spread to staff and community is eventually limited by vaccination – will continue to see children receive unequal levels of teaching and learning.

Combined with other preventive techniques such as testing and the vaccination of teachers and other school staff, as well as novel testing methods such as the regular testing of sewage samples from schools, ventilation can help us take a big step forward in making our schools safer environments for children and staff.