On Tuesday, the World Health Organization (WHO) publicly acknowledged evidence that suggests the coronavirus (SARS-CoV-2) can spread through airborne transmission.

This comes after the agency received an open letter from 239 health experts urging the group to review its guidelines.

“We have been talking about the possibility of airborne transmission and aerosol transmission as one of the modes of transmission of COVID-19,” said technical lead on the COVID-19 pandemic at the WHO, Maria Van Kerkove at a news briefing.

Dr. Benedetta Allegranzi, head of the WHO’s committee on infection prevention and control echoed her statement, reiterating that the possibility of airborne transmission, particularly in “crowded, closed, poorly ventilated settings, cannot be ruled out.”

She also went on to say that scientists at the WHO are currently reviewing evidence on transmission of the virus and plan to release updated information in the coming days. For the time being, the agency recommends “appropriate and optimal ventilation” of indoor environments and adequate physical distancing.

The WHO had previously determined the coronavirus primarily travels through respiratory droplets expelled from the nose and mouth of an infected person that quickly fall to the floor.

However, the open letter that was officially published on Monday in the Clinical Infectious Diseases journal by the group of scientists across 32 countries, suggested “evidence emerging” that small and floating aerosols may cause virus particles to linger in the air and infect people who breathe them in.

“We are very glad that WHO has finally acknowledged the accumulating evidence, and will add aerosol transmission indoors to the likely modes of transmission,” said Jose-Luis Jiminez, co-signatory of the letter and professor of chemistry at the University of Colorado Boulder.

“This will allow the world to better protect themselves and fight the pandemic."

The letter urged the WHO to recommend the public to avoid overcrowding in confined spaces. They also called on public buildings, schools, companies and care homes to supply clean air, minimize recirculating air, consider using strong air filters and virus-killing ultraviolet lights.

“Public health agencies around the world take their cues from WHO, and hopefully this would lead to greater emphasis on wearing of face coverings and avoiding the three Cs: close contact, closed and poorly ventilated spaces and crowds,” said Linsey Marr, an aerosol expert at Virginia Tech.

Despite the health agency’s recent public acknowledgment of the suggestion, the WHO have reportedly had this letter for over a week. Furthermore, the agency has also been sitting on similar reports for the past few months.

This inaction has led to criticism by experts in the field, who have said that the WHO can be slow and risk-averse in adopting precautions as a result of their rigid attitudes.

“They’ll die defending their view,” said one WHO consultant, who added that the agency should relax their criteria for proof given the rapid spread of the virus.

“There is no incontrovertible proof that SARS-CoV-2 travels or is transmitted significantly by aerosols, but there is absolutely no evidence that it’s not. So at the moment we have to make a decision in the face of uncertainty, and my goodness, it’s going to be a disastrous decision if we get it wrong,” said Dr. Trish Greenhalgh, a primary care doctor at the University of Oxford.

Since then, the WHO has defended its delay in assessing the possibility of airborne transmission of the virus explaining that they review 500 new papers a day and ensure the quality of each paper before it is included in their official analysis.

“Any guidance we put out has implications for billions of people around the world. It has to be carefully done,” said Dr. Soumya Swaminathan, the WHOs chief scientist.

Dr. Allegranzi added that the evidence presented at the time had been 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.

Many experts also sympathized with the WHO, citing tricky political relationships and a shrinking budget all while serving as the global hub of virus information.

For the past several months, United States President Donald Trump has been threatening withdrawal from the WHO after accusing them of siding with the Chinese government and defending their early handling of the coronavirus outbreak.

“The world is now suffering as a result of the malfeasance of the Chinese government,” Trump said in May.

On Tuesday, the Trump administration formally gave notice of their departure from the WHO – a move that would put the agency’s budget back by around US$500 million.

“The United States’ notice of withdrawal, effective July 6, 2021, has been submitted to the U.N. secretary general, who is the depository for the WHO,” said a senior administration official.

This formal notification garnered fierce backlash, with many calling the move “disastrous” for national interests and the American influence on international health diplomacy amid a global outbreak.

“I think it’s an extraordinarily bad decision that will both harm global public health and harm the health of the American people,” said Dr. Ashish Jha, the director of the Harvard Global Health Institute.

“It’s unclear to me how the American people benefit by not being at the table and not being able to shape those policies.”

The president of the United Nations (UN) Foundation, Elizabeth Cousens, labeled the US’ move to formally withdraw from the WHO as “shortsighted, unnecessary, and unequivocally dangerous.”

However, the withdrawal will not take effect until next year, after the US presidential election.

As such, Democratic candidate Joe Biden tweeted that he would rejoin the WHO “on my first day as President.”

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