How likely was it for Trump to have infected Biden during the first 2020 presidential debate?

Four days after 2020’s first presidential debate, President Donald Trump announced he and first lady Melania Trump had tested positive for the coronavirus. Because Donald Trump, Vice President Joe Biden, Chris Wallace, and Trump’s family and team were unmasked for the duration of the debate, Xiaoliang Shao and Xianting Li developed a numerical model of the scene to determine the probability of infection for debate attendees at different locations within the hall.

Although they found the probability to be quite low – about 1.66% for seats in front and 0.37% for seats to the right of Melania Trump, and only about 0.34% for Biden and Wallace – they note that, had the Trump family and team worn masks, these values could have been decreased down to 0.09%. They also emphasize that these low numbers are not indicative of typical indoor spaces, due to the excellent ventilation in the building and the lack of contact between attendees.

“If the ventilation rate is lower in the indoor space, the ventilation will be insufficient to dilute the virus content, and the infection risk could be greater than 30% through airborne transmission alone. The infection risk would thus be much greater than the case of the first presidential debate,” Li said. “Therefore, crowded indoor spaces should still be avoided.”

Shao and Li accounted for two potential scenarios in their model: one in which only Donald Trump was infected during the debate, and another assuming both he and the first lady were already infected. They also considered the setup of the space, including the air supply locations and distribution patterns.

Similar infection risk analyses can be extended to various types of confined ventilated indoor spaces.

Source: “COVID-19 transmission in the first presidential debate in 2020,” by Xiaoliang Shao and Xianting Li, Physics of Fluids (2020). The article can be accessed at https://doi.org/10.1063/5.0032847 .