Anyone who has overcome Covid-19, the disease caused by SARS-Cov-2, is protected from a Second Covid-19 reinfection? If yes, how long does immunological protection last? / SARS-Cov-2病毒引起的COVID-19的痊愈患者中，有没有人已获得抵抗二次感染的能力?如果有的话，这种免疫能力会持续多久?