The World Health Organization (WHO) has published an updated scientific brief on the transmission of SARS-CoV-2, the virus causing COVID-19, acknowledging that further study of the potential airborne transmission of the virus is needed.

The organisation has stated that short-range aerosol transmission, particularly in specific indoor locations, such as crowded and inadequately ventilated spaces over a prolonged period, with infected persons, cannot be ruled out.

The report comes after an open letter signed by 239 international scientists was published in the Oxford Academic Journal Clinical Infectious Diseases, calling on the WHO to update its advice. According to the scientists, there is evidence suggesting that exhaled droplets under five micrometres in size containing the virus can become suspended in the air for several hours and travel up to tens of metres.

“Handwashing and social distancing are appropriate, but in our view, insufficient to provide protection from virus-carrying respiratory microdroplets released into the air by infected people,” the authors wrote.