Abstract
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.
Highlights
The COVID-19 outbreak originated in Wuhan, China, in late 2019 before spreading globally to become a pandemic in March 2020 [1]
We run the model in the two scenarios described in Methods: (i) within a quarantine facility to estimate the probability an individual will leave the facility while still infectious and (ii) in the community external to quarantine facilities to estimate the size of an outbreak initiated by an infected frontline worker
We investigate the risk of an infectious individual being released into the community under this regime and under alternative quarantine and testing regimes: scheduled testing of travellers only on departure from their country of origin and arrival in the destination country with no quarantine; 5-day quarantine with testing on day 3; 14-day quarantine with no scheduled testing
Summary
The COVID-19 outbreak originated in Wuhan, China, in late 2019 before spreading globally to become a pandemic in March 2020 [1]. New Zealand experienced an outbreak of COVID-19 between March and May 2020, but successfully controlled the epidemic and eliminated community transmission of the virus for over 100 days [2,3] During this time, the country’s border remained closed to everyone except citizens and residents, with a mandatory 14-day period of government-managed quarantine for all international arrivals. The country’s border remained closed to everyone except citizens and residents, with a mandatory 14-day period of government-managed quarantine for all international arrivals Countries such as Iceland, Taiwan, Vietnam and some states of Australia have reduced cases to very low numbers and are managing the virus with a combination of border controls and domestic restrictions. Other countries managing ongoing epidemics, including several European countries, use border controls including quarantine to reduce the number of imported cases
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