Thread by @Prof_Lowe

1/ The rationale for masks in COVID prevention it a hot topic so I want to provide an overview. Community masking focuses on two mechanisms: source control & inhalation protection @Don_Milton

2/ Masks alone will not stop COVID19 but are an important tool in reducing transmission. When masks are one of a number of measures that together can can stop COVID19

3/ Source Control: Multi-layer cloth masks block exhaled particles & virus particles carry. Cloth masks block large droplets & fine droplets (also often referred to as aerosols) >10 um bit.ly/2UJLRKi 14 studies support this

4/ Source Control: Multi-layer cloth masks both block up to 50-70% of fine droplets3,14  and limit the forward spread of those that are not captured. 4 studies bit.ly/2IUA8Gd

5/ Source Control: People infected with SARSCoV2 are able to infect others for 2-days prior to symptoms start & even when they do not have symptoms. Wearing a mask reduces spread of virus by people who are unknowingly contagious bit.ly/2HgpdWC

6/ Masks as inhalation protection for the wearer: Studies demonstrate that cloth mask materials can reduce wearers’ exposure to infectious droplets through filtration. 15 studies bit.ly/2KpNAT1

7/ Adopting universal masking policies can help avert future lockdowns, especially if combined with other non-pharmaceutical interventions such as social distancing, hand hygiene, adequate ventilation and community measures that limit congregate mask free activities tweet 12-17

8/ Utility of masks: 2 ill hair stylists interacted with 139 clients, none of the 67 clients interviewed developed infection. Stylists & all clients universally wore masks in the salon as required by local ordinance at the time. bit.ly/3nExKlH

9/In a study of 124 Beijing households with > 1 laboratory-confirmed case of SARS-CoV-2 infection, mask use by the index patient and family contacts before the index patient developed symptoms reduced secondary transmission within the households by 79% bit.ly/2UK8ONc

10/Retrospective case-control among more than 1,000 persons, those who reported having always worn a mask during high-risk exposures experienced >70% reduced risk infection compared with persons who did not wear masks under these circumstances. bit.ly/2KgIAzW

11/Outbreak aboard USS Theodore Roosevelt, an environment notable for congregate living quarters & close working environments, found use of face coverings on-board was associated with 70% reduced risk. ncbi.nlm.nih.gov/pubmed/32525850

12/Seven studies have confirmed the benefit of universal masking in community level analyses: in a unified hospital system bit.ly/3kUzmpX 

German cities bit.ly/35JwTdh 

U.S. state bit.ly/3pL3pnh

13/ benefit of universal masking in community level continued

15 U.S. states+Washington, D.C. bit.ly/2UK9TEK bit.ly/3nHWb1w

Canada bit.ly/2IMnDMB 

U.S. bit.ly/3pL72tG

14/Analysis of data from 200 countries that included the U.S. also demonstrated reductions in mortality bit.ly/35J8ynY

15/An economic analysis using U.S. data found that, given these effects, increasing universal masking by 15% could prevent the need for lockdowns and reduce associated losses of up to $1 trillion or about 5% of gross domestic product bit.ly/38Wbpfh

16/Mask mandates increase the percentage of people who wear masks bit.ly/38Wbpfh

17/Mask mandates are associated w declines in case and fatality growth bit.ly/38Wbpfh

18/additional 89 studies on masks are listed here bit.ly/32Zvcqi

CDC scientific brief on the value of community masking bit.ly/2IPlhNe

19/ Danish study found masks did not prevent infections when levels of COVID were low in community and when community wide masking was not in place. Limitation: study didn’t evaluate participants indoor dining habits & made no claims on source control bit.ly/2IUvuIr

20/Case control study of 1800 US participants found primary difference between cases and controls that wore masks was eating & drinking on-site at locations bit.ly/3lMlgbp