Computer code to run the model from Vaccination and testing of the border workforce for COVID-19 and risk of community outbreaks: a modelling study

Throughout 2020 and the first part of 2021, Australia and New Zealand have followed a COVID-19 elimination strategy. Both countries require overseas arrivals to quarantine in government-managed facilities at the border. In both countries, community outbreaks of COVID-19 have been started via infection of a border worker. This workforce is rightly being prioritized for vaccination. However, although vaccines are highly effective in preventing disease, their effectiveness in preventing infection with and transmission of SARS-CoV-2 is less certain. There is a danger that vaccination could prevent symptoms of COVID-19 but not prevent transmission. Here, we use a stochastic model of SARS-CoV-2 transmission and testing to investigate the effect that vaccination of border workers has on the risk of an outbreak in an unvaccinated community. We simulate the model starting with a single infected border worker and measure the number of people who are infected before the first case is detected by testing. We show that if a vaccine reduces transmission by 50%, vaccination of border workers increases the risk of a major outbreak from around 7% per seed case to around 9% per seed case. The lower the vaccine effectiveness against transmission, the higher the risk. The increase in risk as a result of vaccination can be mitigated by increasing the frequency of routine testing for high-exposure vaccinated groups.

2020年至2021年上半年，澳大利亚与新西兰均实施了新冠病毒（COVID-19）消除策略。两国均要求境外入境人员在边境的政府管理设施内接受隔离检疫。两国的新冠社区暴发疫情均由边境工作人员感染引发，因此该群体理应优先接种疫苗。不过，尽管疫苗在预防发病方面效果显著，但其在阻断严重急性呼吸综合征冠状病毒2（SARS-CoV-2）感染与传播方面的有效性尚不明确。存在一种潜在风险：疫苗或可预防新冠相关症状，但无法阻断病毒传播。本研究采用新冠病毒传播与检测的随机模型，探究边境工作人员接种疫苗对未接种疫苗社区暴发疫情风险的影响。我们以单名感染的边境工作人员为初始感染条件开展模型模拟，统计首次通过检测发现病例前的感染人数。研究结果显示，若疫苗可使病毒传播风险降低50%，边境工作人员接种疫苗会使每例初始输入病例引发大规模暴发的概率从约7%升至约9%；疫苗针对病毒传播的防护效力越低，暴发风险越高。通过提高高暴露接种人群的常规检测频率，可缓解接种疫苗带来的风险升高问题。