from the attached critique of the Cochrane Review...
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Epidemiologists Raina MacIntyre, Abrar Ahmad Chughtai, David Fisman, and primary health care professor Trish Greenhalgh detailed the multiple limitations of the Cochrane review in an article for The Conversation. One of these limitations was that most trials included in the review “addressed only half of the question” on mask effectiveness:
"Face masks and respirators work in two ways: they protect the wearer from becoming infected and they prevent an infected wearer from spreading their germs to other people. Most RCTs in this Cochrane Review looked only at the former scenario, not the latter.”
N95/P2 respirators are designed to prevent airborne infections, like COVID-19 and flu, by filtering infectious particles and preventing the wearer from breathing them in. By contrast, surgical face masks mainly work by physically blocking the release of infectious particles from infected individuals into the air (source control)[2], as Health Feedback explained in an earlier review. However, most trials only tested mask effectiveness at preventing infection in the wearer, ignoring the potential benefit of face masks in source control.
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As the authors of the Cochrane review explained in the Discussion, the available RCTs evaluating mask effectiveness were of “variable quality”. For example, some of the trials lacked blinding, while others used unclear randomization methods or poorly defined outcomes to assess the impact of the intervention. Each of these factors increases the risk of bias, reducing the reliability of the meta-analysis’ conclusions. In addition, while some studies confirmed the type of infection by a laboratory test, many others relied on self-reporting to assess both mask-wearing and infection, further increasing the risk of bias.
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Another important limitation of the review is that the RCTs included in the analysis evaluated the effect of face masks on several respiratory viruses in different populations and multiple settings with variable risks of transmission. This variability is already made clear at the beginning of the review:
“[The studies] took place in low-, middle-, and high-income countries worldwide: in hospitals, schools, homes, offices, childcare centres, and communities during non-epidemic influenza periods, the global H1N1 influenza pandemic in 2009, epidemic influenza seasons up to 2016, and during the COVID-19 pandemic.”
But pooling data from such heterogeneous studies together increases the likelihood that any effect gets diluted in the overall variability of the data.
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Further complicating the question is the fact that most of the participants in the individual RCTs didn’t wear face masks consistently during the trial. Instead, most wore masks occasionally or in specific settings, like working places, university residences, or when in contact with people with respiratory infections.
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Better yet, read the attached critique...then read my link of the study published in the NEJM...there is NO QUESTION that masking works...or Baron wouldn't have used them in his work.
Link: https://healthfeedback.org/claimreview/multiple-studies-show-face-masks-reduce-spread-of-covid-19-cochrane-review-doesnt-demonstrate-otherwise/