WHO warms of airborne spread

GENEVA: The World Health Organisation yesterday acknowledged ‘‘evidence emerging’’ of the airborne spread of Covid19, after a group of scientists urged the global body to update its guidance on how the respiratory disease passes between people.

‘‘We have been talking about the possibility of airborne transmission and aerosol transmission as one of the modes of transmission of Covid19,’’ WHO technical lead on the Covid19 pandemic Maria Van Kerkhove told a news briefing.

The WHO has previously said the virus that causes the Covid19 respiratory disease spreads primarily through small droplets expelled from the nose and mouth of an infected person that quickly sink to the ground.

However, in an open letter to the Genevabased agency, published on Tuesday in the Clinical Infectious Diseases journal, 239 scientists in 32 countries outlined evidence that they said showed floating virus particles could infect people who breathe them in.

Because those smaller exhaled particles could linger in the air, the scientists in the group had been urging the WHO to update its guidance.

‘‘We wanted them to acknowledge the evidence,’’ said Jose Jimenez, a chemist at the University of Colorado who signed the paper.

‘‘This is definitely not an attack on the WHO. It’s a scientific debate, but we felt we needed to go public because they were refusing to hear the evidence after many conversations with them,’’ he said in a telephone interview.

Speaking at yesterday’s briefing in Geneva, WHO technical lead for infection prevention and control Benedetta Allegranzi said evidence was emerging of airborne transmission of the coronavirus, but that it was not definitive.

‘‘. . .The possibility of airborne transmission in public settings — especially in very specific conditions, crowded, closed, poorly ventilated settings that have been described, cannot be ruled out,’’ she said.

‘‘However, the evidence needs to be gathered and interpreted, and we continue to support this.’’

Jimenez said historically, there had been a fierce opposition in the medical profession to the notion of aerosol transmission, and the bar for proof had been set very high. A key concern had been a fear of panic.

‘‘If people hear airborne, healthcare workers will refuse to go to the hospital’’, or people would buy up all the highly protective N95 respirator masks, ‘‘and there will be none left for developing countries’’, he said.

Jimenez said the WHO panel assessing the evidence on airborne transmission was not scientifically diverse, and lacked representation from experts in aerosol transmission.

Any change in the WHO’s assessment of risk of transmission could affect its current advice on keeping 1metre of physical distancing. Governments, which rely on the agency for guidance policy, may also have to adjust public health measures aimed at curbing the spread of the virus.

Van Kerkhove said the WHO would publish a scientific brief summarising the state of knowledge on modes of transmission of the virus in the coming days.

‘‘A comprehensive package of interventions is required to be able to stop transmission,’’ she said.

‘‘This includes not only physical distancing, it includes the use of masks where appropriate in certain settings, specifically where you can’t do physical distancing and especially for healthcare workers.’’