Table 5 Scenario analyses covering different source countries, SARS-CoV-2 infection burdens and flight volumes (with the base case for comparison).

From: Estimating the impact of control measures to prevent outbreaks of COVID-19 associated with air travel into a COVID-19-free country

Scenario/country setting

Intervention

Annual risk of outbreak in NZ

Median waiting time until next outbreak occurs (95% range)****

Mean number of flights to create one outbreak#

Australia to NZ (base case) with the historical prevalence in Australia of 48/million (Table 1), 1 flight per day

3 h flight time

None

96.4%

76 d (3 d–407 d)

110

2 PCR in NZ*

42.8%

1.2 y (17 d–6.6 y)

652

3 PCR in NZ**

36.6%

1.5 y (20 d–8.1 y)

800

Quarantine***

13.1%

4.9 y (66 d–26.2 y)

2593

Australia to NZ, as per the historical base case above but with 20 flights per day (slightly more than the pre-pandemic level)

None

100%

4 d (1 d–22 d)

110

2 PCR in NZ*

100%

23 d (1 d–122 d)

652

3 PCR in NZ**

100%

28 d (1 d–150 d)

800

Quarantine***

100%

90 d (3 d–480 d)

2593

Australia to NZ, as per base case but with 1/10 of the historical base case prevalence in Australia: 4.8 / million; (equivalent to a small outbreak from a border failure averaging 7.4 new cases per day)

None

28.3%

2.1 y (28 d–11.1 y)

1099

2 PCR in NZ*

5.4%

12.4 y (165 d–65.9 y)

6520

3 PCR in NZ**

4.5%

15.2 y (203 d–80.9 y)

8005

Quarantine***

1.4%

49.2 y (1.8–262 y)

25,928

Australia to NZ, as per the base case but with the prevalence in Australia closer to March 2021 settings and a border failure generating 2 new cases per week; prevalence 0.18 / million##

None

1.2%

56 y (2–297 y)

29,420

2 PCR in NZ*

0.2%

331 y (12–1760 y)

174,114

3 PCR in NZ**

0.2%

406 y (15–2161 y)

213,809

Quarantine***

0.1%

1,314 y (48–6991 y)

691,710

Japan to NZ, with a prevalence of 163 / million in Japan (Table 1). 1 flight per day, 10.6 h flight time

None

100%

23 d (1–124 d)

34

2 PCR in NZ*

83.0%

143 d (5 d–2.1 y)

206

3 PCR in NZ**

77.0%

173 d (6 d–2.5 y)

249

Quarantine***

34.3%

1.7 y (22 d–8.8 y)

870

US to NZ, with a prevalence of 5,115 / million in the US (Table 1). 1 flight per day, 13 h flight time

None

100%

1 d (1–6 d)

2

2 PCR in NZ*

100%

5 d (1–27 d)

7

3 PCR in NZ**

100%

6 d (1–32 d)

9

Quarantine***

100%

20 d (1–109 d)

29

  1. For each intervention strategy, 1 billion stochastic simulations were run for “Australia base case”, “Australia 20 flights/day” and “Australia 1/10 prevalence”; 100 million simulations for all other country settings.
  2. *Pre-flight saliva test; 2 PCR tests in NZ (on days 1 and 3); until second PCR, passengers wear masks in NZ and self-report symptoms (contacts are traced and quarantined).
  3. **Pre-flight saliva test; 3 PCR tests in NZ (on days 1, 3 and 12); until third PCR, passengers wear masks in NZ and self-report symptoms (contacts are traced and quarantined).
  4. ***Pre-flight saliva test; quarantine of all passengers in NZ for 7 days.
  5. #The median waiting time until an outbreak occurs only refers to the time until a plane lands which will cause an outbreak in NZ; further days are needed until a passenger infects somebody, until the infection spreads in NZ to many others, and until an outbreak is officially declared. Passengers who are found positive during one of the NZ based PCR tests or traced and detected secondary cases do not trigger the declaration of an outbreak. Here, an outbreak is assumed to be the out-of-control spread of SARS-CoV-2 which will reach many cases if not prevented by major interventions.
  6. ##Due to the very low prevalence, no additional simulations were run for this scenario, but the outbreak probabilities per flight were linearly extrapolated from the corresponding base case simulations (based on 1 billion flights each); the reported output was calculated from the obtained probability per flight as detailed in the Supplementary Information.
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