Cochrane 2020
There is uncertainty about the effects of face masks. The low-moderate certainty of the evidence means our confidence in the effect estimate is limited, and that the true effect may be different from the observed estimate of the effect. The pooled results of randomised trials did not show a clear reduction in respiratory viral infection with the use of medical/surgical masks during seasonal influenza. There were no clear differences between the use of medical/surgical masks compared with N95/P2 respirators in healthcare workers when used in routine care to reduce respiratory viral infection. Hand hygiene is likely to modestly reduce the burden of respiratory illness. Harms associated with physical interventions were under-investigated.
Cochrane 2023
There is uncertainty about the effects of face masks. The low to moderate certainty of evidence means our confidence in the effect estimate is limited, and that the true effect may be different from the observed estimate of the effect. The pooled results of RCTs did not show a clear reduction in respiratory viral infection with the use of medical/surgical masks. There were no clear differences between the use of medical/surgical masks compared with N95/P2 respirators in healthcare workers when used in routine care to reduce respiratory viral infection. Hand hygiene is likely to modestly reduce the burden of respiratory illness, and although this effect was also present when ILI and laboratory-confirmed influenza were analysed separately, it was not found to be a significant difference for the latter two outcomes. Harms associated with physical interventions were under-investigated.
CATO Working Paper
We reviewed the mechanistic, observational, and clinical evidence relevant to the use of cloth face masks in community settings to limit the spread of respiratory infections, and in particular the novel SARS-CoV-2 coronavirus. In each area, we found existing evidence inadequate to demonstrate clear benefit (or harm). Mechanistic evidence shows a clear benefit as measured by laboratory surrogates, but it is not clear to what extent those surrogates are relevant to the clinical question of infection rate or offset by behavioral factors. Uncontrolled observational studies are confounded by numerous known and unknown variables, and most considered mask mandates or self-reported mask wearing as the key variable rather than actual mask usage. The infection dynamics of SARS-CoV-2 differ from SARS-CoV-1 and other
respiratory illnesses, meaning that much of the evidence, even if suggestive, has uncertain relevance to SARS-CoV-2. Recommendations to impose mask mandates based on the
precautionary principle fail to account for the possibility that masks cause harm, or that masks may have varying benefits and risks in different settings.Notwithstanding the lack of evidence, in the midst of a pandemic policymakers and public health officials cannot wait until high-quality evidence is generated. However, if they determine based on limited evidence that community masking policies are appropriate, it is an ethical imperative to refrain from portraying the evidence as stronger than it actually is.
Estimates of lives that could potentially be saved, if provided, must be carefully balanced with appropriate disclosure of study limitations and uncertainties. Some models supporting
community face masking suggest large beneficial effects, but these models are based on assumptions that face masks reduce SARS-CoV-2 transmission by 40–50%–– assumptions that are not adequately supported by existing data. More generally, given the low quality of evidence, the absence of statistically significant benefit indicated by most randomized
controlled trials, and the possible harm suggested by a few studies, scientists and public health officials must take care not to apply a double standard to available studies—emphasizing projections of lives saved when evidence suggests benefit, while focusing on study limitations rather than outcomes when the evidence suggests harm or the absence of benefit.
Masking Lack Of Evidence
The small number of trials and lateness in the pandemic cycle is unlikely to give us reasonably clear answers and guide decision-makers. This abandonment of the scientific modus operandi and lack of foresight has left the field wide open for the play of opinions, radical views and political influence.
Sydney Morning Herald 2003
“I’m sure everyone would agree that it is un-Australian to profiteer from people’s fears and anxieties,” Ms Meagher said.
“There appears to be some debate about whether surgical masks are able to minimise the effects of SARS.”
Ms Meagher said her department would investigate any complaints about false mask claims which concerned the public.
“Penalties can range from fines of up to $22,000 for an individual or $110,000 for a corporation,” she said.
Health authorities have warned that surgical masks may not be an effective protection against the virus.
“Those masks are only effective so long as they are dry,” said Professor Yvonne Cossart of the Department of Infectious Diseases at the University of Sydney.
“As soon as they become saturated with the moisture in your breath they stop doing their job and pass on the droplets.”
Professor Cossart said that could take as little as 15 or 20 minutes, after which the mask would need to be changed. But those warnings haven’t stopped people snapping up the masks, with retailers reporting they are having trouble keeping up with demand.
Mr Bell agreed with Professor Cossart’s assessment regarding the effectiveness of the masks.
“I think they’re of marginal benefit,” he said. “In a way they give some comfort to people who think they’re doing as much as they can do to prevent the infection.”
That seems to be the mentality of travellers to Asian destinations, who are buying and wearing the masks while overseas.
Hospital Infection
No evidence was found that removal of a staff/visitor mask-wearing policy had a significant effect on the rate of hospital-acquired SARS-CoV-2 infection. This does not demonstrate that masks were ineffective through the pandemic, but provides some objective evidence to justify the removal of healthcare mask mandates once there was widespread immunity and reduced disease severity.
Re-Analysis of Bangladesh
The purpose of randomized control trials is to establish a causal link between interventions and outcomes. However, causal implications are diminished in the presence of unblinding, ascertainment bias, and bias-susceptible endpoints. Unfortunately, in the Bangladesh mask trial we evidence of all of the above.
The study in question raises intriguing questions about the role of public health interventions in changing behavioral patterns to decrease COVID case rates in low- and middle-income countries. The mask intervention was highly effective at modifying behaviors (distancing, mask-wearing, symptom reporting). Nonetheless, the data is consistent with mask wearing having modest or no direct effect on COVID-related outcomes in this experimental setting.
More On Bangladesh
First, let’s start with basics. There is a reason that the CDC, WHO and Fauci himself advised against community masking in early March 2020— and it was not to protect the supply for health care workers. The true reason is simple: the pre-existing evidence was poor. That’s the opinion of the Cochrane collaboration, and a systematic review that I participated in on the topic. These agencies truly did not believe it would help because that’s just what the evidence said.
How did COVID19 studies change the evidence? Well, there was a sea of low quality observational studies. They are not worth considering, as noise is 2 orders of magnitude larger than signal. I have debunked dozens in these pages and on YouTube.
There was one individual level randomized trial (DANMASK) that failed to find a benefit, but was limited by low power to exclude a small benefit. There were just 2 cluster RCTs run globally— and none pertaining to children.
One cluster RCT has not been published, and the other is the Bangladesh study. Bangladesh is a cluster RCT that randomized adults in villages to free masks (surgical or cloth) and encouragement to wear them or not, and followed people for COVID19 outcomes. The study found surgical masks lowered rates of COVID19 —though the effect is very small and applies only to adults pre-vaccine and pre-natural immunity and not cloth masks.
Enter the re-analysis. The authors noticed that there was a difference in the number of people enrolled in the study. It looked like ~9% more people enrolled in the free mask arm. This 9% is highly significant, i.e. a real difference.
Of course, the purpose of a randomized trial is to minimize confounding and balance outcome distributions in the absence of treatment effect, but imbalance in the size of groups suggests that something might have happened that jeopardizes this fact.
What would cause more people to sign up for the treatment arm (free mask) than control arm? One possibility is that concealment was violated, and people knew that they might get something for free in 1 arm, but did not feel they would get anything in the other arm.
If participants could see a big truck or boxes in intervention villages, but not see that in control villages, they may be more likely to enroll. In fact, 9% more likely!
This has huge implications. Is the extra 11th person in the mask arm the same as the 10 people in control arm? Or is this the type of person that only enrolls on the margin? Only enrolls if they are getting something for free, but not otherwise, and thus slightly less likely to properly report COVID symptoms (perhaps they report less or differently) and less likely to follow through with testing?
The authors argue this is possible, and this threatens the entire trial. Assuming these people are just a little different, can cause the entire trial results to tip. Their paper nicely probes this statistically and is worth your time.
I have one separate question about this study. The strongest secondary endpoint— the only one truly bias resistant— is random seroprevalance (which does not rely at all on reporting). This endpoint remains listed on ClinicalTrials.gov, but unreported. It must be completed and reported.
Is a mask necessary in the operating theatre?
No masks were worn in one operating theatre for 6 months. There was no increase in the incidence of wound infection.
Chamberland Filter
Worth noting that viruses were only discovered because they could pass through porcelain filters, which bacteria could not.
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