The role of masks in preventing respiratory infections in healthcare settings

MacIntryre, C. R. et al., (2025) summarised by Amanda Harrington-Vail

Introduction

The COVID-19 pandemic brought face masks into the global spotlight, but guidance on their use often changed and was sometimes conflicted. Early in the pandemic, governments and health organisations disagreed on when and what type of masks to wear, leading to confusion and misinformation. Mask use was mandatory in many countries at the beginning of the COVID-19 pandemic. Although guidance about which masks should be used was inconsistent, resulting in various products being used, some of which were ineffective at stopping the spread of infection. Reviewers examined the effectiveness of mask and respirator effectiveness in healthcare, community, and special settings in preventing respiratory infections.

This state of the art review included English language studies published between 1950–2023 which included randomised controlled trials, also observational, case control and laboratory studies. Guidelines from the World Health Organization (WHO), the US CDC and the UKHSA along with guidelines from other health organisations were included. They referred to articles from PubMed, Embase, Cochrane Library, Web of Science, and Google Scholar. The Australian New Zealand Clinical Trials Registry (ANZCTR) and the US National Institutes of Health clinical trial registry were also searched. The GRADE (Grading of Recommendations Assessment, Development and Evaluation) approach was used to examine the type of evidence. They also searched infection control policies and guidelines from WHO, the US CDC, the UK Health Security Agency, and other health organisations to identify recommendations on the use of masks and respirators, with a focus on changing policies over the course of the pandemic. Additionally, searching literature from health organisation websites and Google for policies and guidelines on the use of masks and respirators.

Summary

Clarification of mode of transmission for respiratory diseases

One reason guidance about masks/respirators was inconsistent and inaccurate during the early days of the COVID-19 pandemic was a lack of understanding about how the virus was transmitted. The review states that infection protection and control (IPC) guidance is often based on experiments from the 1950s and an outdated understanding of modes of transmission. Experts now agree that COVID-19 is airborne. The review authors call for IPC guidance to be updated to reflect this and to take into account their other findings.

Effectiveness of different types of masks and respirators

The occupational health and safety hierarchy of controls state removal of the worker from the hazard as more important than personal protective equipment (PPE). However, reviewers point out that healthcare workers “must treat patients with deadly infectious diseases”. This context and the importance of respirators for healthcare workers has never been explicitly recognised in IPC guidelines.

Respirator face masks, like N95/N99 (or FFP2/FFP3 as they are called in the UK), were shown to offer the highest level of protection against respiratory diseases. These tightly fitting masks filter out tiny airborne particles and are most effective when worn consistently by healthcare workers in high-risk environments. Laboratory based studies show low filtration efficiency of medical masks compared with respirators, which provided 8-12 times greater protection. Mask effectiveness is influenced by proper fit, comfort, supply availability and clear communication. Fit testing is important for respirators. The review also found that masks not only help prevent the wearer from getting sick but also reduce how much virus an infected person breathes out.

Other mask types offer less protection. Medical masks (the thin blue ones often referred to as surgical masks) only provide moderate protection blocking larger droplets and are less effective than respirators, especially against airborne viruses like COVID-19. Cloth masks offer the least protection but are better than nothing with their performance varying depending on materials and washing methods, but they can still reduce infection risk when no other options are available. During shortages, extended use or layering masks can offer additional protection. Medical and cloth masks have gaps so contaminated air can enter.

Many infection prevention and control guidelines still advise that masks/respirators only need to be worn when carrying out what was thought to be a high risk procedure. However, the findings of this review indicate that healthcare workers need to wear respirators throughout their shift to be properly protected. Wearing masks/respirators only during specific procedures or when patients show symptoms does not provide effective protection, particularly as people can be contagious even before they show symptoms and others may be infectious but asymptomatic.

Effectiveness of masks in the community

In the community, any mask is helpful during outbreaks. When used widely and early on in an epidemic, especially with hand hygiene, masks reduce infection spread. Respirators are most protective, followed by medical masks, then cloth masks.

The effectiveness of mask mandates

Since people can pass on viruses like COVID-19 before they feel ill, universal masking during high transmission periods is a practical and protective strategy. Indeed, the review recommends the precautionary principle is adopted.

Children benefit from wearing masks too, but evidence is limited

While no major studies focused solely on children, existing evidence suggests that, when worn properly, masks can protect children and reduce spread in schools.

Cost effectiveness of high quality PPE

Availability of high-quality PPE is one of the most important organisational factors in a pandemic, cheaper and less effective PPE can end up being costlier in the long run. Studies included in the review report the cost-effectiveness of respirators, their use reduced hospital acquired infections and deaths, plus cut patient bed days and staff replacement needs.

Conclusion

Government and health organisation guidance on masking was inadequate, resulting in the further spread of COVID-19. Respirators provide 8-12 times greater protection than medical masks. Wearing masks/respirators only during specific procedures or when patients show symptoms cannot provide effective protection, people can be contagious before they show symptoms and others may be infectious but asymptomatic. Universal masking during high transmission periods is a practical and protective strategy. Mask policies are commonly static and fail to consider increased understanding as scientific developments occur, therefore pandemic policies need to be regularly updated.

As infection protection and control (IPC) guidance is frequently based on 1950s experiments, plus outdated understanding of transmission modes, IPC guidance needs urgent review reflecting that COVID-19 is airborne. Reviewers indicate that healthcare workers “must treat patients with deadly infectious diseases” therefore they require protective respirators, which has not been identified in IPC guidelines. Strong leadership is required to overcome politicisation and division around masks. Further review on respirator design, protective function, material and proper use is needed.

Read the full Clinical Review here