COVID-19: Double masking can block 92% of infectious particles - US CDC

The US Centers for Disease Control and Prevention (CDC) has found close-fitting surgical masks worn underneath cloth masks – known as double masking – can significantly enhance protection against Covid-19.

This is the first CDC-backed research to recommend “double-masking”, although the nation’s top infectious disease expert, Dr Anthony Fauci, has recommended the public consider the measure in past briefings.

“There’s nothing wrong with people wearing two masks,” Fauci said at a press briefing one week before the research was released. “I often myself wear two masks.”

The CDC study found the most protective masks fit well around the face “to prevent leakage of air around the masks edges”, and also recommended knotting ear loops near the facial covering portion of the mask to contour the mask closer to the face.

The study did not look at the effectiveness of respirators, like N95s, and most health authorities recommend the public continue to reserve respirators for medical personnel.

This CDC study compared wearing no mask, a poorly fitted surgical mask, cloth-only mask and double-masking in a simulation of respiratory droplets between two people – a source and a receiver.

The study found when people wear a well-fitted surgical mask covered by a cloth mask, they can increase their own protection from aerosol droplets by 90% or more, and that possible transmission is significantly reduced when both parties wore masks.

“Universal masking is a highly effective means to slow the spread of Sars-CoV-2 when combined with other protective measures, such as physical distancing, avoiding crowds and poorly ventilated indoor spaces, and good hand hygiene,” the study found.

Importantly, the study also had limitations. The findings are not generalizable to men with beards and facial hair, which can interfere with masks, or to children, whose faces are smaller. As well, the study did not compare two surgical masks or two cloth masks, and the study looked at only one type of cloth mask, though there are many types of mask on the market.

Fourteen states and Washington DC have universal masking policies. The Joe Biden administration also recently ordered masks be worn on all federal grounds and on domestic transport. Biden called on all Americans to wear masks for the first 100 days of his presidency, calling it a “patriotic duty”.

Recent forecasts have also begun to take universal masking into account. If 95% of people wore masks in public, forecasters at the Institute for Health Metrics and Evaluation believe more than 116,000 lives could be saved by 1 June, compared with the institute’s “worst-case” scenario, in which 702,000 people could die from Covid-19.

The CDC first recommended the public wear cloth masks in April 2020, about one month after the American north-east was hit hard by the virus. At the time, those recommendations were vague, asking Americans to consider wearing masks, “fashioned from household items or made at home from common materials at low cost”.

While the science on face coverings is “advancing rapidly”, a recent review in the Proceedings of the National Academy of Sciences noted face coverings have been worn to contain airborne pathogens since the 13th century.