Sinovac Biotech plans to start a clinical trial of its experimental coronavirus vaccine with children and adolescents later this month, widening its test on a shot that's already in the final stage of study with adults.Finding a vaccine that works for the entire population, including younger people, could be crucial to preventing outbreaks of the virus - that has led to over 930,000 deaths worldwide - through schools and kindergartens, potentially affecting also teachers and parents.A total of 552 healthy participants aged between three and 17 will take two doses of U.S.-listed Sinovac's CoronaVac or a placebo in a combined Phase 1 and Phase 2 trial estimated to begin on Sept.