SHANGHAI (Reuters) -Shanghai said on Friday it has brought China’s worst outbreak of COVID-19 under effective control following a month-long lockdown of nearly 25 million people, with authorities vowing to stand by their zero-COVID strategy despite mounting economic costs. The number of new COVID infections in China’s financial hub had been on a “continuous downward trend” since April 22, the city’s vice major Wu Qing said. “Currently, our city’s epidemic prevention and control situation is steadily improving, and the epidemic has come under effective control,” he told a news conference. Many …