The protests against police brutality and racism that have spread across the US have spurred fears that they could result in a resurgence of the virus. Concerns have forced people sympathetic to the movement to weigh the risks of attending demonstrations, where there is often little social distancing. Health experts know that the virus is far less likely to be spread outdoors than indoors. And masks reduce the chances of respiratory droplets containing the virus being transmitted. But yelling, shouting and singing can increase how far those droplets are projected. Crowds also increase the risk of transmission.