Amid a frightening rise in new Covid-19 cluster infections, 239 experts have written an open letter to the WHO, outlining evidence showing that smaller airborne particles containing the virus can infect people, The New York Times reported on Sunday.

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, the experts said, the coronavirus is borne through air and can infect people when inhaled.

The scientists from 32 countries are calling on the UN health agency to revise its recommendations and plan to publish their letter in a scientific journal.

If airborne transmission is a significant factor in the pandemic, especially in crowded spaces with poor ventilation, the consequences for containment will be significant, NYT reported. Masks may be needed indoors, even in socially distant settings. Health care workers may need N95 masks that filter out even the smallest respiratory droplets as they care for coronavirus patients, it said.

Ventilation systems in schools, nursing homes, residences and businesses may need to minimise recirculating air and add powerful new filters. Ultraviolet lights may be needed to kill particles floating indoors.