Six scientists from the University of California, Davis, said their findings suggested more quiet zones in high-risk indoor spaces – such as hospitals and restaurants – could benefit efforts to curb the disease’s spread.

The World Health Organisation amended its guidance in July to acknowledge the possibility of aerosol transmission, such as during choir practice, or when in restaurants or fitness classes.

The new research showed microscopic droplets ejected while speaking evaporate to leave behind aerosol particles big enough to carry viable virus.