The corona finds new victims worldwide, in bars and restaurants, offices, markets and casinos, causing terrifying cases, confirming more and more what many scientists have been saying for months: The virus stays in the air indoors, infecting those found close.
If airborne transmission is an important factor in pandemics, especially in crowded areas with insufficient ventilation, the consequences for restriction will be significant. Masks may be needed indoors, even in socially remote locations.
Ventilation systems in schools, nursing homes, homes and businesses may need to minimize air recirculation and require strong new filters.
The World Health Organization has long argued that the coronavirus is spread mainly by large respiratory droplets that, when left by infected people with coughing and sneezing, quickly fall to the floor.
However, in an open letter to the WHO, 239 scientists from 32 countries have outlined the data that shows that smaller particles can infect humans and ask the body to reconsider its recommendations. The researchers plan to publish their paper in a scientific journal next week.
Even in its most recent update on the coronavirus, released on June 29, the WHO said the airborne transmission of the virus is possible only after medical procedures producing aerosols or droplets of less than 5 microns. (One micron is equal to one millionth of a meter.)
Dr. Benedetta Allegranzi, the W.H.O.’s technical lead on infection control, said the evidence for the virus spreading by air was unconvincing.
“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 said. “There is a strong debate on this.”
“We have known since 1946 that coughing and talking create aerosols,” said Linsey Marr, a specialist in airborne transmission at Virginia Tech.
Scientists have not been able to develop coronavirus from aerosols in the laboratory. But that doesn’t mean aerosols aren’t contagious, Dr. Marr said. “Most of the samples in these experiments come from hospital rooms with good airflow that will dilute virus levels.”
In most buildings, she said, “the rate of air change is usually much lower, allowing the virus to accumulate in the air and pose a greater risk.”
“They’ll die defending their view,” said one longstanding W.H.O. consultant, who did not wish to be identified because of her continuing work for the organization. Even its staunchest supporters said the committee should diversify its expertise and relax its criteria for proof, especially in a fast-moving outbreak.
“I do get frustrated about the issues of airflow and sizing of particles, absolutely,” said Mary-Louise McLaws, a committee member and epidemiologist at the University of New South Wales in Sydney.
“If we started revisiting airflow, we would have to be prepared to change a lot of what we do,” she said. “I think it’s a good idea, a very good idea, but it will cause an enormous shudder through the infection control society.”
The WHO relies on a dated definition of airborne transmission, said Dr. Marr. The agency believes that an airborne pathogen, such as the measles virus, must be highly contagious and travel long distances.
Dr Marr and other scientists said the coronavirus appeared to be more contagious when humans were in prolonged contact at close range, especially indoors and even more so at events overpopulated – just what scientists would expect from aerosol transmission.