The "most comprehensive study to date" found that physical distance and perhaps the use of a mask were the two best ways to prevent transmission of the new coronavirus.

The new study, published in the Lancet medical journal Monday, found people should stay at least three feet apart and more if possible.

The review of various published studies, paid for by the World Health Organization, had three main findings:

Physical distancing: The chance of transmission at a distance of less than 1 meter (3.3 feet) was 12.8%, while that fell to 2.6% at a distance of more than 1 meter (3.3 feet).

It said that the certainty of the evidence was "moderate." Face masks: The chance of transmission without a face mask or respirator (like an N95 mask) was 17.4%, while that fell to 3.1% when a mask was worn.

For health care workers, the study found that N95 masks and other respirator-type masks might give greater protection from viral transmission than surgical masks or multilayered cotton or gauze masks.

She said the general public should wear a cloth mask or standard surgical mask, leaving respirator masks for health care workers.

Even when properly used and combined, distancing, masks and eye protection do not offer complete protection, the study stressed, and basic measures like hand washing are essential to reduce transmission.