Masks, no evidence they work

RCTs did not show a clear reduction in respiratory viral infection with the use of medical/surgical masks.

There were no clear differences between the use of medical/surgical masks compared with N95/P2 respirators in healthcare workers,

when used in routine care to reduce respiratory viral infection.

Do physical measures such as hand-washing or wearing masks stop or slow down the spread of respiratory viruses?

Evidence published up to October 2022.

Background

Influenza (H1N1) caused by the H1N1pdm09 virus in 2009

Severe acute respiratory syndrome (SARS) in 2003

Coronavirus disease 2019 (COVID-19)

Update of a Cochrane Review last published in 2020.

We include results from studies from the current COVID-19 pandemic.

Main results

11 new RCTs and cluster-RCTs n = 610,872

Bringing the total number of RCTs to 78

Medical/surgical masks compared to no masks

Wearing masks in the community probably makes little or no difference to the outcome of influenza‐like illness

wearing a mask may make little to no difference in how many people caught a flu-like illness/COVID-like illness

Risk ratio (RR) 0.95, (0.84 to 1.09)

9 trials, n = 276,917 participants

Moderate-certainty evidence.

Wearing masks in the community probably makes little or no difference to the outcome of laboratory-confirmed influenza/SARS-CoV-2

RR 1.01, (CI 0.72 to 1.42)

6 trials, n = 13,919

Moderate-certainty evidence

Harms were rarely measured and poorly reported

(very low-certainty evidence).

N95/P2 respirators compared to medical/surgical masks

We pooled trials comparing N95/P2 respirators with medical/surgical masks

We are very uncertain on the effects of N95/P2 respirators compared with medical/surgical masks on the outcome of clinical respiratory illness

Compared with wearing medical or surgical masks, wearing N95/P2 respirators probably makes little to no difference in how many people have confirmed flu and may make little to no difference in how many people catch a flu-like illness, or respiratory illness.

Confirmed influenza

RR 0.70, (0.45 to 1.10)

N = 7,779

Very low-certainty evidence

Influenza like illness

N95/P2 respirators compared with medical/surgical masks may be effective for ILI

RR 0.82

N= 8,407

Low-certainty evidence

The use of a N95/P2 respirators compared to medical/surgical masks

Probably makes little or no difference for laboratory-confirmed influenza infection

RR 1.10

N = 8,407

Moderate-certainty evidence

Restricting pooling to healthcare workers made no difference to the overall findings.

Harms were poorly measured and reported

Discomfort wearing medical/surgical masks or N95/P2 respirators was mentioned in several studies

Very low-certainty evidence

One new RCT

Medical/surgical masks were non-inferior to N95 respirators

N = 1,009 healthcare workers in four countries,

providing direct care to COVID-19 patients.