Last reviewed 28 July 2020

Over 200 international scientists have written an open letter to the World Health Organization (WHO) urging the agency to issue appropriate warnings about the risks posed by airborne Covid-19 particles, known as aerosols.

The letter refers to mounting evidence which suggests that tiny viral particles which linger in the air in indoor spaces are a significant source of coronavirus infection, according to the 239 experts who wrote the letter, published online on 6 July 2020 in the journal Clinical Infectious Diseases.

The authors note that the WHO’s focus has been on handwashing, maintaining social distancing and respiratory droplets on surfaces.

They argue that while these recommendations are appropriate, they are insufficient to provide protection from virus-carrying respiratory microdroplets released into the air by infected people, particularly in enclosed or crowded environments with poor ventilation.

The letter states, “There is significant potential for inhalation exposure to viruses in microscopic respiratory droplets (microdroplets) at short to medium distances (up to several meters, or room scale), and we are advocating for the use of preventive measures to mitigate this route of airborne transmission.”

The paper adds, “Studies by the signatories and other scientists have demonstrated beyond any reasonable doubt that viruses are released during exhalation, talking, and coughing in microdroplets small enough to remain aloft in air and pose a risk of exposure at distances beyond 1 to 2 metres (yards) from an infected individual.”

The WHO indicated on 7 July 2020 that it planned to review its advice in relation to airborne coronavirus particles.