WHO released a new "Scientific Brief" on Transmission of SARS-CoV-2 today. New recommendations are a mixed bag, some good to hear but others are a real problem. https://www.who.int/publications/i/item/modes-of-transmission-of-virus-causing-covid-19-implications-for-ipc-precaution-recommendations Read on for my take on this. @UMDPublicHealth @President_Pines

First -- the good. WHO included the recommendations to “Avoid ... enclosed spaces with POOR VENTILATION;” and that we should “ENSURE GOOD VENTILATION in indoor settings, including homes and offices.” I'm really happy to see this.

But... they only recommend face masks when within one meter of other people. This is very bad advice, especially in "enclosed spaces with poor ventilation."

How did they get to making this terrible suggestion?
It comes from ...

This terrible recommendation comes from the fundamental problem with the new WHO “scientific brief;" they do not use fact-based science to define “respiratory droplets” and “aerosols.” They only cite their own previous statements, not peer-reviewed scientific literature.

WHO's definition of "respiratory droplets" and "aerosols" represents their biased outdated opinions rather than current scientific facts and echoes medical dogma dating to an influential medical textbook published over 100 years ago.

The extensive research and tremendous progress in the physics and biology of aerosols since 1940 appears to have had no impact. The contention that “respiratory droplets” in the size range of >5 to 10 µm in diameter only travel up to 1 meter is absolutely wrong.

The contention that “respiratory droplets” in the size range of >5 to 10 µm in diameter only travel up to 1 meter is medical folklore without a shred of scientific evidence. It is absolutely critical that the WHO use scientific facts to update their recommendations.

Peer-reviewed scientific publications clearly demonstrate that particles even as large as 30 µm can move on air currents and travel more than 10 meters indoors. Even droplets as large as 100 µm can be inhaled and lodge in the nose.

And, even if you only consider droplets less than 5 µm – recent studies of influenza virus show that people with influenza infection breath out more virus in the <5 µm size range than in droplet aerosols larger than 5 µm.

The report points out that SARS-CoV-2 RNA has been detected in air, but that the virus has not been cultured from air – but it ignores that this same argument was made about influenza virus for years ... until...

– until two groups, one at CDC-NIOSH and one at the University of Maryland demonstrated that influenza virus can be cultured from the air. None of this important literature was considered by the WHO.