HONG KONG, June 21 (Reuters) - Hong Kong said on Monday it would shorten the quarantine period for vaccinated people arriving in the city to seven days from 14, provided travellers show sufficient antibodies against the novel coronavirus. City government leader Carrie Lam told a media briefing the shorter period of quarantine would only be for people who had a second vaccination does at least 14 days before their arrival. The new rule is due to come into effect from the end of the month, she said. The Chinese-ruled city has some of the toughest quarantine rules globally with residents ordered to stay for up to 21 days in quarantine hotels after arriving. The decision to reduce the time in quarantine comes as the city tries to encourage more of its 7.5 million people to get COVID-19 vaccinations. Only about 17% of residents have been fully vaccinated since February. The government said the new rule would apply to Hong Kong residents from June 30 and to non-residents some time in July. For those arriving from countries deemed "very high risk", the quarantine period remains unchanged at 21 days. Health Secretary Sophia Chan told the briefing some social distancing measures, including limits on numbers in restaurants and bars, would be eased from June 24 for vaccinated residents. Hong Kong authorities have over the past month urged businesses and financial institutions to encourage their staff to get vaccinated and urged them to give employees a day off for their shots. Many companies offer staff rewards for vaccinations while some have threatened to deny pay rises or even to lay off workers if they don"t get the shots. nL2N2NL0FB] The former British colony has largely controlled the virus with about 11,800 infections and 210 deaths. The city has a surplus of unused vaccines and some of the shots are about to expire, the government said.