It's an issue that's been argued about for months: Can people who don't feel sick spread the coronavirus, and if so should we all be wearing masks to stop it? Even the [WHO] can't seem to get it straight. On Tuesday the U.N. health agency scrambled to explain seemingly contradictory comments it has made in recent days. On Friday, WHO changed its mask advice, recommending that people wear fabric masks if they could not maintain social distancing, if they were over age 60 or had underlying medical conditions. Part of the reasoning, WHO officials said, was to account for the possibility that transmission could occur from people who had the disease but weren't yet symptomatic. But when Maria Van Kerkhove, WHO's technical lead on COVID-19 was asked about the frequency of this kind of transmission this week, she said It still appears to be rare that asymptomatic individuals actually transmit onward." The details on how well the coronavirus spreads in different circumstances is not well understood. Can people who don't feel sick spread the disease? We don't know. WHO has maintained for months that the vast majority of COVID-19 spread is from people with symptoms like a fever or cough, and that transmission from people who don't feel sick is not thought to be a major driver of the disease. Does wearing a mask help? Probably. Why don't we know for sure? It's complicated. Truly asymptomatic people are likely not responsible for significant virus spread. Detailed studies ... are needed. Although numerous studies have suggested people can spread the virus before they show symptoms, WHO has largely dismissed those as anecdotal or pointed out that they were based on modelling.