The World Health Organization (WHO) has long held that the coronavirus is spread primarily by large respiratory droplets that, once expelled by infected people in coughs and sneezes, fall quickly to the floor.

But in an open letter to the WHO, 239 scientists in 32 countries have outlined evidence showing that smaller particles can infect people, and are calling for the agency to revise its recommendations. The researchers plan to publish their letter in a scientific journal next week, The New York Times says.

Even in its latest update on the coronavirus, released June 29, the WHO said airborne transmission of the virus is possible only after medical procedures that produce aerosols, or droplets smaller than 5 microns. (A micron is equal to one millionth of a meter.)

But interviews with nearly 20 scientists — including a dozen W.H.O. consultants and several members of the committee that crafted the guidance — and internal emails paint a picture of an organization that, despite good intentions, is out of step with science.

Whether carried aloft by large droplets that zoom through the air after a sneeze, or by much smaller exhaled droplets that may glide the length of a room, these experts said, the coronavirus is borne through air and can infect people when inhaled.