Extending the quarantine to 10 days is equivalent to 1 highly infectious case being released into the community every 100 days on average.

Scenario 4 Model

A 5-day quarantine period detects as many cases as the full 14-day period but is not as effective in preventing highly infectious cases reaching the community. A 5-day quarantine leads to 6.8% of arrivals who are highly contagious being inappropriately released. This is equivalent to 1 case reaching the community every 9 days. 

Scenario 3 Model

Testing only upon arrival and departure detects 64% of arriving infected cases.

Scenario 2 Model

Testing only upon arrival only detects 53% of arriving infected cases. 

Scenario 1 Model

Extending the quarantine to 14 days (which is the current policy) equated to 1 highly infectious COVID-19 case being released into the community every 600 days. If interpersonal contact is allowed within the quarantining facilities, this risk can rise to 1 every 27 days, which is why separating people during quarantine is essential.

Scenario 5 Model

Exemptions do pose a small risk, especially early exemptions lowing for early exemptions which may release highly contagious cases into the community. Therefore reducing interpersonal contact within the government quarantine facility is essential.

Scenario 6 Model

Late exemptions (in the second week only) pose less of a risk since the individual has been quarantined for a significant amount of days already. 

Scenario 7 Model

Graph of impact of different quarantine lengths

Graph of impact of exemptions on 10 and 14 day quarantine

7 scenarios were mathematically modeled in order to predict what the pandemic will look like New Zealand once border reopen.
- Scenario 1: Test on Arrival Only
- Scenario 2: Test on Arrival and Departure
- Scenario 3: Five Day Quarantine 
- Scenario 4: 10 Day Quarantine 
- Scenario 5: 14 Day Quarantine (Currently being employed)
- Scenario 6: Exemptions Allowed
- Scenario 7: Late Exemptions Allowed

Northwestern University

This study investigates the effectiveness of New Zealand's travel restrictions- specifically the closing of the border to everyone except citizens and residents. It then analyzes 7 different extremes in terms of travel restrictions and models what their effects would be on the amount of re-incursion from international arrivals. 
- Background information
- Results from Observed Data
- Future: 7 scenarios
- Discussion

The effect of border controls on the risk of COVID-19 reincursion from international arrivals

Steyn N., Binny R., et al. The effect of border controls on the risk of COVID-19 reincursion from international arrivals. 22 July 2020. BioRxiv. https://doi.org/10.1101/2020.07.15.20154955

7 Scenarios

From 9th June 2020, arrivals in New Zealand MIQ facilities have been tested twice, once around day 3 and once around day 12 (Ministry of Health, 2020). We consider the two-week period between 23rd June and 6th July, during which all individuals have been subject to these requirements for their entire stay. 

Results from Observed Data

A mathematical modeling study evaluating border controls for COVID-19 reincursion risk found that a period of $$ 14 $$ days of managed isolation or quarantine (MIQ) reduces the risk of releasing an infectious case into the community to a very low level. Combined with testing on day $$ 3 $$ and day $$ 12 $$, daily symptom checks, and complete isolation of confirmed cases, the risk is approximately $$ 0.1 \% $$ per arriving case. The greatest reduction to risk involves minimizing interaction among arrivals.

Impact of Managed Isolation and Quarantine on COVID-19 Reincursion Risk

New Zealand imposed strong border restrictions, forbidding all non-residents since March $$ 20 $$. All arrivals have a $$ 14 $$-day imposed quarantine in government facilities where they are monitored and tested for COVID-19 on days $$ 3 $$ and $$ 12 $$. Now that restrictions have been lifted, it is critical to consider the impact that overseas cases may have, as a rapid outbreak may occur. This study utilized mathematical models to predict several outcomes.

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