As China steps up efforts in the global campaign to develop a coronavirus vaccine, the National Bio-tec Group and Sinovac say four more countries have agreed to run late-stage trials of their vaccine candidates. Serbia and Pakistan will take on Phase 3 trials of the CNBG vaccines. While Sinovac's vaccine candidate will be trialed in Brazil and Indonesia. CNBG says Phase 3 trials have begun in about 10 countries including the UAE, Bahrain, Peru and Argentina. They are expected to involve 50,000 people. Phase 3 clinical trials usually require thousands of people to verify the safety and effectiveness of vaccines. They are key to their market approval.