Scientists say coronavirus is airborne in letter to WHO
Over 200 experts have written to the World Health Organization, urging the health agency to recognize airborne transmission of the coronavirus and change its recommendation. The WHO acknowledges airborne transmission in cases of healthcare workers during medical procedures that produce aerosols. However, in an open letter to the WHO, 239 scientists from 32 countries outlined that the virus can be transmitted through smaller particles.
To support their claims that the coronavirus is airborne, the scientists have cited evidence, they plan to publish their letter in a scientific journal this week, The New York Times reported. Experts told NYT that the coronavirus is transmitted via air, be it through large droplets from a sneeze or cough, or smaller exhaled droplets that "may glide the length of a room."
According to the WHO's latest update on COVID-19, released on June 29, airborne transmission of the virus is possible only after medical procedures that produce aerosols, or droplets smaller than 5 microns. The agency prioritizes frequent hand washing to limit the spread of the viral disease. However, it has been found that the probability of infection through surfaces is low.
WHO's technical lead on infection control, Dr. Benedetta Allegranzi, told NYT the evidence that coronavirus is airborne is unconvincing. She said, "Especially in the last couple of months, we have been stating several times that we consider airborne transmission as possible but certainly not supported by solid or even clear evidence." She added, "There is a strong debate on this."
Back in April, 36 experts on air quality and aerosols had urged the WHO to consider growing evidence of airborne transmission. The expert group's leader, Lidia Morawska, and a WHO consultant were then called for a meeting. However, at the time, WHO experts continued to stress the importance of handwashing, which ended up being prioritized over aerosols.
Speaking to NYT, Dr. Linsey Marr, an expert in airborne transmission of viruses at Virginia Tech University, said that the WHO's definition of airborne transmission is dated. "The agency believes an airborne pathogen, like the measles virus, has to be highly infectious and to travel long distances," the report said. Marr also questioned the studies the WHO relied on to rule out airborne transmission.
Marr said that scientists have not been able to grow the coronavirus from aerosols in the lab, but those samples come from hospital rooms that have good airflow that dilutes viral levels. She argued that most buildings have worse air-exchange rates, allowing the virus to accumulate. She added that the scientific community has known since 1946 that coughing and talking generate aerosols.
Several experts agreed that airborne transmission does not mean that the virus will hang in the air for many hours and travel long distances. But aerosols may remain suspended in the air, increasing the risk, particularly for poorly-ventilated enclosed spaces that are crowded. This is buttressed by instances of superspreader events in enclosed spaces. This means that masks may be needed indoors.
WHO's chief scientist Dr. Soumya Swaminathan said the agency is trying to evaluate new evidence quickly without sacrificing the quality of their review. "We take it seriously when journalists or scientists or anyone challenges us and say we can do better than this," she said.