After conducting various experiments on dummies, the US Center for Disease Control and Prevention (CDC) announced that exposure to potentially infectious aerosols decreased by about 95% when tightly fitted masks were worn.
Tightly fitted masks included using a cloth mask over a medical procedure mask, knotting the ear loops of the medical mask, and tucking in the extra material close to the face.
Both modifications “substantially improved source control and reduced wearer exposure,” stated the CDC in an early release.
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According to the CDC, COVID-19 is transmitted predominately by respiratory droplets expelled when people cough, sneeze, sing, talk, or breathe.
Masks are primarily intended to stop these virus-laden droplets from escaping (called “source control”), but they also help to reduce the inhalation of droplets by the mask-wearer (called “personal protection”).
The former is especially important for asymptomatic or pre-symptomatic individuals who, the CDC says, account for more than 50% of virus transmissions.
“The community benefit of masking for SARS-CoV-2 control is due to the combination of these effects,” the brief stated. “Individual prevention benefit increases with increasing numbers of people using masks consistently and correctly.”
Some materials, such as polypropylene, may make filtration more effective by generating a form of static electricity that better captures charged particles, the CDC found.
Others, like silk, may help repel droplets, keeping masks dry, breathable, and comfortable.
“Individual benefit increases with increasing community mask use,” according to the brief.
“Adopting universal masking policies can help avert future lockdowns, especially if combined with other non-pharmaceutical interventions such as social distancing, hand hygiene, and adequate ventilation.”