On April 24, 2021, the Centers for Disease Control and Prevention issued new guidance on outdoor activities. In subsequent testimony before the US Senate, a number reported in our article, “Outdoor Transmission of SARS-CoV-2 and Other Respiratory Viruses: A Systematic Review,” was cited that the proportion of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission occurring in outside settings is less than 10%.

We are writing to clarify how we arrived at the less than 10% summary number. Our abstract and results sections state that “five identified studies found a low proportion of reported global SARS-CoV-2 infections occurred outdoors (<10%).” Because of the small number of heterogeneous studies we reviewed, as well as their methodological limitations, we could not provide a meta-analytically pooled estimate of the exact proportion of SARS-CoV-2 transmissions that have occurred outdoors or the associated risk.