Eight confirmed COVID-19 reinfections have been reported worldwide since the pandemic began, but experts say it is "not a surprise at all".
A 33-year-old man from Hong Kong was hospitalised with COVID-19 in March. Four months later, he tested positive again despite not showing any symptoms.
Dr Nikki Turner, director of the Immunisation Advisory Centre at the University of Auckland, told The Project it's not a surprise repeat infections occur.
"We know with other similar respiratory viruses that very occasionally, people don't mount an effective immune response and they can get reinfected," she said.
"There are always individuals out there who do not respond with a really vigorous immune response. There's a whole lot of reasons for that and we don't have enough cases to know why these ones got the case again."
Dr Turner says while the COVID-19 vaccine is developing, it is important to know that it is only one strategy that is going to help protect us against the virus.
"The early vaccines are looking promising. They do show that when you give them to individuals, that most people look like they mount a good response," she said.
"Vaccines are not 100 percent effective, they're not going to be the total magic bullet. They're just going to be part of our answer."