This lack of clarity about the risks of fomites — compared with the much bigger risk posed by transmission through the air — has serious implications. People and organizations continue to prioritize costly disinfection efforts, when they could be putting more resources into emphasizing the importance of masks, and investigating measures to improve ventilation. The latter will be more complex but could make more of a difference.

The New York City Metropolitan Transit Authority alone estimates that its annual COVID-related sanitation costs will be close to US$380 million between now and 2023. Late last year, the authority asked the US federal government for advice on whether to focus solely on aerosols. It was told to concentrate on fomites, too, and has so far directed more resources towards cleaning surfaces than tackling aerosols.

Now that it is agreed that the virus transmits through the air, in both large and small droplets, efforts to prevent spread should focus on improving ventilation or installing rigorously tested air purifiers. People must also be reminded to wear masks and maintain a safe distance. At the same time, agencies such as the WHO and the CDC need to update their guidance on the basis of current knowledge. Research on the virus and on COVID-19 moves quickly, so public-health agencies have a responsibility to present clear, up-to-date information that provides what people need to keep themselves and others safe.