Masks did not prevent infection

The pooled results of 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?

https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD006207.pub6/full

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.