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A new letter in Science intensifies the controversy about the transmission of the coronavirus: the “evidence is overwhelming”, but they are unable to agree

Harry Watson

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“There is overwhelming evidence that inhalation of SARS-CoV-2 represents a major route of transmission for COVID-19 .” For this reason, “there is an urgent need to harmonize the debates on the modes of virus transmission” and “to guarantee the most effective control strategies and provide a clear and consistent guide to the public opinion.” With these words, the letter that Kimberly Prather and five other colleagues have just published in the prestigious journal Science begins .

For months now, the toughest scientific controversy in the pandemic has been over how the virus is transmitted and the implications this has on our efforts to combat it. Scientists who believe that aerosols are the priority route and those who think that this is not yet confirmed have been in the middle of an all-out war for weeks through academic journals, media and social networks.

Prather’s letter may seem like one more installment in this battle and, in many ways, it is; But it is something more: a wake-up call to make an effort on both sides and find a ‘framework’ that allows an agreement on the issue to be reached .

What does the letter say?

In the text, the authors, experts in the field of aerosols, emphasize the need to clarify the terminology to distinguish between aerosols and droplets using a new threshold adapted to the available evidence. In other words, change the reference size from the traditional five micrometers to 100. As they explain , “this size is more effective in understanding aerodynamic behavior, inhaled capacity and the effectiveness of interventions.”

Why? Mainly, because while virus droplets larger than 100 microns generally fall to the ground in seconds, so physical distancing reduces exposure to them, viruses capable of being transmitted in aerosols (less than 100 microns) can remain suspended in the air for much longer .

That is, they can travel much more than two meters of the safety distance. “You are much more likely to inhale aerosols than a drop, ” the authors explain , calling for more attention to be paid to protection against airborne transmission. This entails influencing the need to move as many activities as possible to the open air, improve the air in the enclosing spaces through ventilation and increase the quality of the masks in high-risk workers.

A battle that leads nowhere

Even before the letter was made public, the noise around it has been enormous. Each side has interpreted it as their own victory. However, there is a message in the text that we must not ignore. It is time to “harmonize the terms of the debate” and defuse the controversy using the available data. Having dozens of top-level scientists facing off helps no one, especially in the middle of a pandemic.