Cloth masks may help prevent transmission of the SARS-CoV-2 virus by at least partially blocking droplets expelled by people when they speak, cough and sneeze, researchers say.

While the weave of cloth masks may not be tight enough to block individual virus particles, most virions spread in aerosols (smaller than 5 micrometers) or larger droplets, Canadian authors write in the Annals of Internal Medicine.

And there is ample evidence that the masks can prevent such droplets from getting into the air or onto surfaces, they say in an opinion piece after reviewing the literature on cloth masks.

While there is no direct evidence yet that cloth masks can reduce SARS-CoV-2 transmission, they write, the collective evidence indicating that mask-wearing by infected people reduces contamination is convincing and should inform policy.