Leading newspapers published fake news about the effectiveness of masks, based on a BMJ study. The titles speak of a substantial decrease in “Covid incidence”, but editors of the scientific journal deny this conclusion and say that it is evidence of “low or very low” quality.
An article entitled “Effectiveness of public health measures in reducing the incidence of Covid-19, SARS-CoV-2 transmission and Covid-19 mortality: a systematic review and meta-analysis ” served as a motto for several media outlets to reproduce the news that masks “reduce Covid incidence by 53%”.
The study published by the BMJ has several gaps and deficiencies, which lead the authors themselves to acknowledge that they had difficulty establishing “a directional or causal conclusion”.
The meta-analysis from which the medium value of 53% is taken includes only six studies and only one RCT (randomized controlled study). The rest are of lower quality (none at low risk of bias).
Interestingly, the conclusions of the authors of this RCT, carried out with high quality masks and with properly instructed participants, were:
“Our results suggest that the recommendation to wear a surgical mask when outside home, among others, did not, at conventional levels of statistical importance, reduce the incidence of SARS-CoV-2 infection in mask users in an environment where social distancing and other public health measures were in place, mask recommendations were not among these measures, and community use of masks was uncommon.”
Editor’s clarification
In an editorial about the publication entitled “Lack of good research is a pandemic tragedy”, it is highlighted:
“The effects seen in observational studies of mask use will be indistinguishable from other protective behaviors not accounted for during adjustment, …”
“…the quality of the current evidence would be classified – by GRADE criteria – as low or very low, as it consists mainly of observational studies with deficient methods (bias in outcome measurement, PHSM classification and missing data) and high heterogeneity of the effect size. More and better investigations are needed.”
Fact-checking
Fullfact , a fact -checker funded in part by Facebook, has looked into the topic.
He specifically referred to The Guardian, New Scientist and Forbes, and confirmed that they had used a false title .
Note: The news link released by New Scientist is no longer online, without any justification.
In Portugal, the news was also published by the newspaper Publico , with the following title – “Mask reduces incidence by 53% and may be mandatory again in Portugal”.
Anti-disinformation mechanisms
As far as we have been able to find out, there has been no notification, or censorship, to those who transmit this false information. It continues to be freely disseminated in the media, on social networks and in internet searches.
