File images of Chinese health workers in hazmat suits -- referred to as "big whites" in China -- disinfecting a residential compound in Shanghai. A top city official earlier this month lauded disinfectant spraying as a key part of a "grand assault" on the virus, as China continues to pursue a zero-Covid strategy. But experts say the measure is futile against Covid-19, which spreads through droplets expelled in coughs and sneezes into the air. FILE IMAGES of workers disinfecting Shanghai compound