Ankara, July 6 : The phase-2 trials of Turkey's locally developed vaccine against Covid-19 have started in the country's largest city of Istanbul, local media reported. Volunteers aged between 18 and 59, who do not have serious chronic diseases, are included in the trial which began on Monday, Xinhua news agency quoted the local Sabah newspaper as saying. The newspaper report said that the phase-2 trials include 330 volunteers, while experts plan to increase this number to approximately 15,000 in phase-3. The vaccine is reportedly expected to be used in the fall in case of successful results obtained in all the phases. Last week, Turkey started to inoculate healthcare workers and people aged 50 and above with the third dose of Covid-19 jabs as part of the ongoing nationwide vaccination campaign. So far, the number of citizens who received at least one dose of the Covid-19 vaccine reached 53.6 million across the country with a population of 83 million, according to the Health Ministry. /IANS