COVID-19 pandemic were protected from reinfection for up to 28 days later, a Chinese study out Thursday in the journal Science said.While the monkeys displayed initial immunity, it's unclear how long such immunity will last in humans - it will be necessary to wait months, or even years, to know if the millions of people infected at the start of the pandemic are protected from re-infection.Scientists from Peking Union Medical College performed an experiment on rhesus macaques, often used because of their similarities to humans, to find out if they have a short-term immunity to the virus.Six rhesus macaques were infected in their trachea with a dose of the SARS-CoV-2 virus.