No evidence to support these 'statistics' about effectiveness of face masks, expert says
A graphic has been viewed hundreds of times in multiple posts on Facebook, Instagram, Twitter, and Weibo that claim it shows the difference in the COVID-19 transmission rate between individuals who are wearing or not wearing face masks. The claim is misleading; there is no evidence to support the statistics in the graphic, an epidemiologist said; as of July 17, 2020, international health authorities have not published any data on the effectiveness of face masks in curbing the spread of COVID-19.
The graphic was published here on Facebook on April 27, 2020. It has been shared more than 150 times since.
The graphic suggests masks could cut the risk of COVID-19 transmission. It claims that the transmission rate between a COVID-19 carrier and a non-carrier is 100 percent, which can drop to 1.5 percent if both parties wear masks.
A warning written in simplified Chinese at the bottom of the graphic states: “Please refuse to interact intimately with anyone who are not wearing masks / all types of masks would work”.
Under the graphic, a simplified Chinese-language banner emphasises
"the difference between wearing and not wearing a mask / when both parties are masked, the transmission rate is the lowest, at 1.5% only”.
Hu Zhaoming, the spokesperson for China's Bureau of Public Information and Communication, also tweeted an English version of the graphic, asking the netizens to “make your own decision after careful study of this illustrated picture”.
The claim, however, is misleading.
Effectiveness of face masks
Professor Benjamin John Cowling, head of Division of Epidemiology and Biostatistics at the University of Hong Kong, said there is no evidence to support the statistics cited in the graphic.
“Masks are effective, but I think those numbers [in the graphic] overestimate the effectiveness of masks,” he told AFP by email on July 16, 2020.
Regardless of whether the wearer has been infected with COVID-19 or other communicable diseases, surgical masks can reduce but not eliminate “virus-laden particles” passing through the mask into a person’s lungs or into the environment, Professor Cowling added. “Some masks are better than others, and some particle sizes can be filtered more effectively than others."
No official statistics
Neither the US Centers for Disease Control and Prevention (CDC), nor the World Health Organization (WHO), have published official statistics about the effectiveness of face masks in the face of the COVID-19 pandemic.
The CDC advises the general public to wear cloth face coverings to reduce the spread of COVID-19, while healthcare workers are required to wear surgical masks, according to information on the CDC's website here.
As stated here in the WHO’s interim guidance on the use of masks in the context of COVID-19, published on June 5, 2020, “WHO continues gathering scientific data and evidence on the effectiveness of different masks use and on its potential harms, risks and disadvantages, as well as its combination with hand hygiene, physical distancing and other IPC measures."
Hong Kong guidance
In response to the misleading posts, a spokesperson for the Hong Kong Department of Health told AFP by email on July 16, 2020: “Droplet transmission occurs when a person is in close contact of within 1 metre and exposed to potentially infective respiratory droplets through coughing or sneezing.”
The spokesperson declined to comment on the percentages listed in the graphic.
As of July 17, 2020, the Hong Kong Department of Health urged the public to wear surgical masks in crowded areas.