In an attempt to maintain the elimination of COVID-19 in New Zealand, all international arrivals are required to spend 14 days in government-managed quarantine and to return a negative test result before being released. We model the testing, isolation and transmission of COVID-19 within quarantine facilities to estimate the risk of community outbreaks being seeded at the border. We use a simple branching process model for COVID-19 transmission that includes a time-dependent probability of a false-negative test result. We show that the combination of 14-day quarantine with two tests is highly effective in preventing an infectious case entering the community, provided there is no transmission within quarantine facilities. Shorter quarantine periods, or reliance on testing only with no quarantine, substantially increases the risk of an infectious case being released. We calculate the fraction of cases detected in the second week of their two-week stay and show that this may be a useful indicator of the likelihood of transmission occurring within quarantine facilities. Frontline staff working at the border risk exposure to infected individuals and this has the potential to lead to a community outbreak. We use the model to test surveillance strategies and evaluate the likely size of the outbreak at the time it is first detected. We conclude with some recommendations for managing the risk of potential future outbreaks originating from the border.

为了继续消除新西兰的新冠病毒 (COVID-19)，所有国际入境者都必须接受政府管理的隔离 14 天，并在出院前提供阴性检测结果。我们对检疫设施内的 COVID-19 测试、隔离和传播进行建模，以估计在边境传播社区疫情的风险。我们对 COVID-19 传播使用简单的分支过程模型，其中包括假阴性测试结果的时间相关概率。我们证明，只要检疫设施内没有传播，14 天隔离与两次检测相结合对于防止传染病病例进入社区非常有效。较短的隔离期，或仅依赖检测而不隔离，大大增加了感染病例被释放的风险。我们计算了在两周逗留期间第二周发现的病例比例，并表明这可能是衡量检疫设施内发生传播可能性的有用指标。在边境工作的一线工作人员面临着接触感染者的风险，这有可能导致社区爆发。我们使用该模型来测试监测策略并评估首次发现时爆发的可能规模。最后，我们提出了一些管理未来可能源自边境的疫情爆发风险的建议。