In an online guide published on Jan. 11, the Public Health Agency of Canada flatly contradicted the Quebec government, which had claimed three days earlier that air purifiers are useless, or even harmful, in preventing the spread of COVID-19. This is false: air purifiers are a perfectly acceptable “complementary measure” where ventilation is poor, the agency confirmed. This is not the first time that the Quebec government and public health authorities have spread false information.

On Jan. 8, Education Minister Jean-François Roberge and Dr. Richard Massé, an adviser to Quebec’s health ministry, stated that air purifiers could not be recommended for use in the classroom and that these appliances could be a “danger” to students if poorly installed. “COVID-19: No to air purifiers in schools,” read the Journal de Québec the following day, correctly relaying the government’s message.

“The effectiveness of filtration devices in relation to the transmission of infectious diseases in residential or institutional settings has not yet been demonstrated. It is therefore impossible to know whether the use of such devices reduces the transmission of pathogens that could be transmitted by aerosols,” states a report put together at the request of the health ministry.

“Additionally, in properly ventilated spaces, these devices are useless and may even pose further risk by interfering with the function of existing ventilation systems. Finally, they may generate significant air currents that could become problematic, specifically by promoting increased dispersal of larger aerosols and altering airflow if a mechanical ventilation system is already in place.”

At the press conference, Dr Massé, who led the expert panel that assembled the report, doubled down. “Although many people have talked about it, the panel does not recommend it…. Putting a device in a classroom just doesn’t work. It’s a false sense of security. There would need to be one close to everyone.”

These statements shocked Shelly Miller, a professor of mechanical engineering at the University of Colorado Boulder who is recognized as one of the world’s leading authorities on aerosol transmission.

“It’s almost like this information is coming from some anti-science Twitterbot designed to increase transmission of CoV-2,” she tweeted. She pointed out that the United States’ Centers for Disease Control and Environmental Protection Agency recommend the use of air purifiers in poorly ventilated spaces. But given the current political situation south of the border, Canadians might not have much faith in information from U.S. institutions, she noted wryly.

Additional protection

But American scientists are not the only ones to support the use of air purifiers. In a letter calling for the authorities to recognize the importance of aerosol transmission, 363 experts from across Canada argued that air purifiers should be another tool in the fight against COVID-19 — a perspective now endorsed by the Public Health Agency of Canada.

“When properly used, portable air filtration devices with high-efficiency particulate air (HEPA) filters have been shown to reduce the concentration of some viruses from the air,” the Public Health Agency notes in a document titled “COVID-19: Guidance on indoor ventilation during the pandemic.”

“The use of these devices could be considered as an additional protection in situations where enhancing natural or mechanical ventilation is not possible.”

There is no mention of any potential “danger.” The effectiveness of air filtration devices against the novel coronavirus has not yet been proven, the Public Health Agency adds, but it is reasonable to believe that they can be useful. There is no reason, then, not to rely on them when ventilation is poor.

This perspective is shared by the Office of the Chief Science Advisor to Canada, Mona Nemer.

“There is a robust body of research that can be drawn from regarding the use of portable air filtration units to reduce disease transmission,” stated one report released by the office in September. Concerning the alleged danger of air filtration devices, Nemer pointed out that kitchen knives are also dangerous. All it takes is proper use to cut vegetables without slicing your own fingers.

“In circumstances where ventilation cannot be improved through the building heating, ventilation, and air conditioning (HVAC) system, other options like … portable air filtration devices to reduce airborne aerosols could be helpful,” the report adds.

A track record of confusion

Dr. Richard Massé’s claims about the “dangers” of air filtration devices recall similar comments made at the beginning of the pandemic by Dr. Horacio Arruda, Quebec’s director of public health, regarding masks. It is also worth remembering that Mona Nemer criticized Quebec’s lack of transparency regarding its testing strategy. Dr. Arruda responded by saying that Nemer should essentially mind her own business. “I do not believe that I am accountable to this woman,” he said in a tone bordering on contempt.

Two weeks earlier, the Quebec government had flirted with the disastrous strategy of “herd immunity,” which consists of letting people contract the virus freely in the hopes that the population will eventually become immune. Theresa Tam, director of the Public Health Agency of Canada, finally intervened, saying “it’s not a concept that should be supported.”

Confusion often seems to characterize public health officials — and by extension the government — in Quebec. On that same Friday, Jan. 8, the Institut national de
santé publique du Québec (INSPQ) released a report stating, “At this time, there is no direct evidence to clearly demonstrate a mode of airborne transmission for SARS-CoV-2.”

The INSPQ is likely playing with words by stating that there is no “direct” proof, since the evidence is overwhelming. Even the World Health Organization, which is often slow to catch up to evolving science, has recognized it for six months now: “COVID-19: WHO confirms risk of airborne transition of the virus,” its site reported in July.

Flanked by Dr. Massé, Minister Roberge presented the conclusions of the expert panel, stating that air quality was only a concern in three per cent of classrooms… because a CO2 level of 2,000 parts per million (ppm) had only been detected in three per cent of classes. But 2,000 ppm is an astronomical figure. Experts from Harvard’s T.H. Chan School of Public Health, who are authorities on the matter, confirmed that the target level for a normal sized classroom occupied by 15 teenagers should be approximately 700 ppm, indicating five to six air changes per hour, which is the target to avoid aerosol-based contagion. Other experts estimate that a rate of up to 800 ppm is acceptable, but certainly not the 1,000 ppm threshold set by Quebec’s expert panel and based on a standard established prior to the pandemic.

The Quebec study fails in more than one respect. Though 58 per cent of Quebec’s schools have no ventilation system, the study focused on those schools that do, which inevitably skews the averages. Those numbers could have been adjusted to account for the selection bias, but the authors simply didn’t bother. During the school day, half of the classrooms without a ventilation system had CO2 levels greater than 1,000 ppm.

Sending children to school in such an environment is essentially taking the “calculated risk” of increasing community transmission of COVID-19, as Premier François Legault has acknowledged.

Though the government may suggest otherwise, there is significantly more “student-to-community” transmission than the other way around. With statistics to back them up, Simona Bignami, a professor in the department of demography at the Université de Montréal, and her colleagues have recently found that in Montreal, “transmission of COVID among school children/children of schooling age does not seem to be a result of, but rather a major factor in, the general infection rates of neighboring communities.” In other words, students are becoming infected at school and transmitting the virus throughout their community.

This winter, as the majority of schools remain poorly ventilated and the government refuses to resort to imperfect but effective measures such as air purifiers in defiance of the Environmental Protection Agency and Centres for Disease Control in the U.S., the Chief Science Advisor to Canada and now the Public Health Agency of Canada, students will continue to contract COVID-19 and spread it to their families and communities.