Airborne transmission warning,

239 scientists raise danger of airborne transmission

While there’s still much to learn about the coronavirus one thing scientists have been certain of for months is how the disease is transmitted.

World Health Organisation (WHO) guidance states the virus has infected 11.3 million people through either inhaling respiratory droplets from an infected person who is close by, or by touching a surface contaminated with the virus and then touching your eyes, nose or mouth.

The WHO has said the potential for Covid-19 to spread via aerosol transmission — which involves much smaller particles that can remain in the air for long periods of time, and carried over distances further than one metre — is 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 clear evidence,” the WHO’s technical lead on infection control, Dr Benedetta Allegranzi, said.

The WHO has said introducing measures to guard against aerosol transmission is infeasible and unlikely to make much difference to the spread of infection.

But in an open letter set to be published in a scientific journal this week, 239 scientists from 32 countries have accused the WHO of underplaying airborne transmission’s risk, particularly in poorly ventilated rooms or confined spaces like public transport.

The scientists, some of whom have previously advised the WHO, say emerging evidence from settings like abattoirs, where there have been major outbreaks, suggest airborne transmission could be important than the WHO has acknowledged.

“We’ve known since 1946 that coughing and talking generate aerosols,” expert in airborne transmission of viruses at Virginia Tech, Dr Linsey Marr, told The New York Times.

Dr Marr said the WHO had relied on studies from hospitals that suggested low levels of virus in the air, underestimating the risk because in most buildings “the air-exchange rate is usually much lower, allowing virus to accumulate in the air”.

Along with some of the other scientists, Dr Marr said coronavirus seemed to be most infectious when people were in prolonged close range, especially indoors, or in “superspreader” events.

The scientists said if the WHO didn’t update its view on the threat of airborne transmission, there would need to be a major adjustment to existing efforts to contain the virus.

Revisiting the risk of airborne transmission will “cause an enormous shudder through the infection control society”, UNSW epidemiologist Mary-Louise McLaws said.

If airborne transmission is deemed a significant factor in the pandemic, the “consequences for containment will be significant”, the Times said.

Masks could be required indoors, even in socially-distant settings, and ventilation systems in schools, nursing homes and businesses could be required.