No surprises this month that all four new entries to the top ten most read articles in BMJ Open are COVID-19 related—either directly or indirectly—as are two that have maintained their previous positions.

A new entry has taken the top spot, reporting the results of an investigation into reusable face masks worn by frontline medical staff in Vietnam. As SARS-CoV-2 infection rates climb around the world, stocks of essential personal protective equipment (PPE) for hospital and clinic workers are often at precarious levels and shortages can put medical staff at risk, further stretching care systems. The volume of disposable PPE used also has environmental consequences. Reusable equipment may mitigate the environmental impact and relieve shortages but it needs to be safe and effective. The study by MacIntyre and colleagues is a secondary analysis of data from a randomised controlled trial that showed healthcare workers wearing two-layered cloth masks had a higher risk of respiratory tract infection from rhinoviruses than those in N95 medical masks. However, MacIntyre and colleagues looked at the washing methods of the cloth masks and found that the staff whose masks had been washed in the hospital laundry were no more likely to contract rhinovirus infection than those wearing disposable medical masks, but self-washing the masks put staff at more than double the risk of infection.

Still on the subject of cloth mask effectiveness, O’Kelly and colleagues debut at number three with an investigation into the ability of 20 different types of cloth to filter ultrafine particles at coughing velocity. To reduce pressure on stocks of medical grade PPE, people have been advised by various health systems to make their own coverings, and for many communities this approach is their only option. Effectiveness of home-made masks is likely to be variable due to design and material. O’Kelly and colleagues found that single layer cloth masks filtered around 35% of particles, whereas 45% could be stopped by double layering. Adding a non-woven material as a filter, such as a washable HEPA filter or a portion of a vacuum bag, gave up to 11% further protection. However, fibres from these materials could be unsafe to inhale. Furthermore, breathing is slightly more difficult than when wearing an N95 mask. Nevertheless, doubling layering with a filter could offer a degree of protection when needed.

Key to the debate about whether masks should be worn is understanding the mechanisms of transmission. The potential for airborne particulate matter to help spread the SARS-CoV-2 virus is the subject of our new entry at number nine. Setti and colleagues investigated the relationship between COVID-19 patterns in northern Italy in March and airborne concentrations of PM₁₀  (inhalable particles with a diameter of 10µm or less) and found that the frequency of breaching daily limits of 50µg/m³ had a significant association with spread of COVID-19.

Aside from the physical health effects of COVID-19, there are growing concerns that the restrictions, constant negative news and economic uncertainties are having a major impact on mental health. Plenty of research has been underway on this topic since the start of the pandemic. Our tenth most read paper is another new entry that outlines a plan to draw much of this information together with a systematic review and meta-analysis. The review will summarise studies on the effects of the pandemic on the mental health of young people and adults around the world. The study described in this protocol paper has yet to be completed but will undoubtedly make compelling and important reading when it is published.

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