SAN SALVADOR, Sept 24 (Reuters) - El Salvador will begin administering a third dose of COVID-19 vaccine to various groups including the elderly, healthworkers and people with underlying health conditions, President Nayib Bukele said on Friday. The Central American nation of roughly 6.4 million people has obtained some 12 million vaccines since February. Third shots would be given to people including those aged over 60, frontline health staff, teachers, the armed forces, police and firefighters, as well as Salvadorans with pre-existing health problems, Bukele said on Twitter. "Considering the success of the third dose in Israel, we have decided to start with a third dose in El Salvador," the president said, noting the government would enable people to start making appointments for the jabs from Sunday. El Salvador joins a growing group of Latin American nations that are giving booster shots to certain groups of at-risk people, including Panama, Ecuador and Chile. read more