With the opening of a quarantine-free travel corridor between New Zealand and Australia this week, it’s easy to forget COVID-19 is still spreading globally, faster than ever, with more than three million deaths recorded worldwide.
Within a day of the travel bubble opening, a fully vaccinated border worker who cleans planes coming from countries with high rates of COVID-19, tested positive and was transferred to a quarantine facility.
Such cases show why it remains absolutely essential to maintain strict border measures to keep the virus out of the trans-Tasman bubble.
Since January 1 2021, 397 international arrivals in New Zealand have tested positive for the virus. Most have been contained in managed isolation and quarantine (MIQ) facilities.
But we have seen some cases leak out from the border. These fall into two main categories: returnees leaving managed isolation while still infectious and frontline border workers becoming infected with the virus.
To consider the effectiveness of various border policies, we pulled together data on transmission of COVID-19 and rates of false negative test results into a mathematical model. The research, published today, allowed us to quantify the risk of community outbreaks under different quarantine and testing regimes.
Managing risk from international arrivals
Our research shows that a 14-day stay in managed isolation, with tests on day three and day 12, is highly effective in stopping international arrivals from re-introducing COVID-19 into the community. Under this regime, most border cases are either detected and isolated until recovery, or are no longer infectious by the end of their 14-day stay.
By comparison, reducing the time spent in managed isolation would greatly increase the risk. We found that with a five-day stay, around 25% of cases would still be infectious when they entered the community.
Given recent arrival numbers, this would mean multiple border-related cases in the community every week. Sooner or later a major outbreak like Auckland’s August cluster would be inevitable.
Genome sequencing tells us the Auckland outbreak is a single cluster — except for one case
Managing risk from frontline border workers
The research also looked at various testing regimes for frontline border workers. We found that weekly routine testing roughly doubles the chance an infection will be detected while it still has a clear link to the border.
The recent case of a worker at the Grand Millenium MIQ facility was an example of this.
When we find a case with a clear link to the border, typically only a small number of people are infected. The outbreak can usually be contained through contact tracing without the need to raise the alert level.
On the other hand, if border workers are not tested regularly, it increases the chance the outbreak could spread into the community. This means a large number of