The study of more than 6,000 Danes contributes new knowledge about the extent to which face masks protect the wearer against corona infection when the mask is used as a supplement to the authorities’ other recommendations against corona infection – including social distance, hand hygiene and isolation of patients with COVID- 19.
In the DANMASK-19 study, one half of the participants were selected to wear a surgical face mask when they were outside the home, and the other half of the participants were not to wear a mask. All participants were strongly encouraged to follow all other authorities’ recommendations regarding COVID-19.
Mask use outside the health care system was unusual (<5%) in Denmark at the time.
After one month of follow-up, 1.8% of the participants in the mask group and 2.1% of the participants in the control group had an infection. The study thus does not confirm the expected halving of the risk of infection of the wearer of the mouthpiece, but the results could indicate a more moderate degree of protection of 15-20% – however, the study can not rule out that the mask does not protect the wearer.
Researchers from Copenhagen University Hospital recruited 6,024 adults who spent at least three hours a day outside their homes in a function that did not require the use of a mask. Participants should not have symptoms of COVID-19 or have previously had COVID-19. The participants came by lottery either in the mask group or in the control group, and the participants in the mask group were sent free surgical masks.
Participants conducted weekly questionnaire surveys. Nasal and pharyngeal inoculation and antibody testing (self-testing) were used to examine whether the participant had developed SARS-CoV-2- (corona) infection during the course. At the end of the experiment, there was no statically significant difference in infection rates between the two groups.
The study took place in April and May 2020. It must be emphasized that the Danish authorities at that time did not recommend the use of masks outside the health service, and the use of masks was only seen to a modest extent. Public transport and shops remained open while certain institutions and workplaces were closed, and the authorities’ recommendations also included quarantine of people with COVID-19, social distance, limitation of contacts, frequent hand hygiene and cleaning and limited visitors to hospitals and nursing homes. . Restaurants and cafes were closed until May 18th.
According to the study’s authors, the results show the degree of protection that mask wearers can expect when others are not wearing masks and where other general recommendations against COVID-19 were applicable.
It is emphasized that the study did not examine the function of the masks as a source control, ie. to limit infection from an infected person wearing a mask to others. The study also did not elucidate the effect of bandages in situations where it is not possible to maintain the social distance.
It should therefore be emphasized that these results can not be used to cast doubt on the widespread use of masks outside healthcare to be an effective means of reducing SARS-CoV-2 infections.
The editors of the prestigious journal Annals of Internal Medicine motivate their choice to publish the DANMASK-19 study by considering it a well-designed study that is an important piece in the puzzle of how to fight the COVID-19 pandemic. At the same time, the editors note that the US Centers for Disease Control (CDC) recently updated their guidelines that when wearing masks by everyone, they can reduce the risk of infection through both source control and personal protection. They assess that the findings of the DANMASK-19 study do not comply with these guidelines, but that any contribution to risk reduction through personal protection is likely to be less than through source control.
Professor, chief physician, dr.med. Henning Bundgaard, Rigshospitalet, together with professor, chief physician, dr.med. Kasper Iversen, Herlev-Gentofte Hospital, led the researchers behind the study.
Henning Bundgaard and Kasper Iversen can be contacted via Kommunikation og Presse, Rigshospitalet, at:
The above summary is not intended to replace the full article as a source of information.
Material from the journal Annals of Internal Medicine:
The press release has been prepared in collaboration between the authors and the journal.
The study is sponsored by the Salling Foundations.