https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article A May 2020 meta-study on pandemic influenza published by the US CDC found that face masks had no effect, neither as personal protective equipment nor as a source control.

https://swprs.org/face-masks-evidence/ Danish RCT study

https://www.cebm.net/covid-19/masking-lack-of-evidence-with-politics/ no evidence for the effectiveness of cloth masks against virus infection or transmission.

https://www.uea.ac.uk/about/-/new-study-reveals-blueprint-for-getting-out-of-covid-19-lockdown mask requirement was of no benefit and could even increase the risk of infection.

https://www.cidrap.umn.edu/news-perspective/2020/04/commentary-masks-all-covid-19-not-based-sound-data University of Illinois concluded face masks have no effect in everyday life, neither as self-protection nor to protect third parties

https://www.nejm.org/doi/full/10.1056/NEJMp2006372 cloth face masks offer little to no protection in everyday life.

https://www.medrxiv.org/content/10.1101/2020.03.30.20047217v2 An April 2020 Cochrane review (preprint) found that face masks in the general population or health care workers didn’t reduce influenza-like illness (ILI) cases.

https://www.medrxiv.org/content/10.1101/2020.04.01.20049528v1 "evidence is not sufficiently strong to support widespread use of facemasks”

http://www.asahi.com/sp/ajw/articles/13523664 Japanese researchers found that cloth masks “offer zero protection against coronavirus”

https://bmjopen.bmj.com/content/5/4/e006577 A 2015 study in the BMJ Open found cloth masks may increase infection risk

https://www.upi.com/Top_News/World-News/2019/02/01/Millions-in-Japan-affected-as-flu-outbreak-grips-country/9191549043797/ Japan, despite widespread use of masks, had influenza epidemic

https://www.acpjournals.org/doi/10.7326/M20-6817 The recommendation to wear surgical masks to supplement other public health measures did not reduce the SARS-CoV-2 infection rate among wearers.