New Zealand’s COVID-19 elimination strategy

On 23 March 2020, New Zealand committed to an elimination strategy in response to the COVID-19 pandemic. That was the day Prime Minister Jacinda Ardern announced that on 26 March New Zealand would commence an intense lockdown of the country (the highest level of a 4-level response framework¹). At the time, New Zealand had just over 100 COVID-19 cases and no deaths, so this ‘go early go hard’ approach surprised many. However, there were compelling reasons  for New Zealand to pursue elimination².

In this perspective article we describe why an elimination strategy made sense for New Zealand, the distinguishing features of this approach, some of the challenges and how they can be overcome, and where to from here.

Elimination and other strategic choices

Until early March 2020, New Zealand’s response to COVID-19 followed its existing pandemic plan,  based on a mitigation approach for managing pandemic influenza³. The plan includes steps designed to slow entry of the pandemic (keep it out), prevent initial spread (stamp it out), and then apply physical distancing measures progressively to ‘flatten the curve’ and avoid overwhelming health services (manage it). Because pandemic influenza cannot be contained (except by extreme measures such as total border closure), there was a presumption that case and contact based management would fail and the country would inevitably progress to having widespread community transmission of the pandemic virus Sars-CoV-2.

Most western countries across Europe and North America were following the mitigation approach.  However, it was performing poorly, with COVID-19 cases overwhelming health services. Most countries were then switching to a suppression strategy ⁴. This strategy involved intense physical distancing and travel restrictions (lockdowns) to suppress virus transmission.  A few countries were continuing with a version of mitigation labelled ‘herd immunity’ where they planned to manage the rate of infection in such a way as to avoid overwhelming the health care system and build up enough recovered and likely immune people in the population to ultimately interrupt virus transmission. This approach proved difficult to manage and was largely abandoned (except perhaps by Sweden).

Most low and middle-income countries could do very little to manage the pandemic except apply limited mitigation measures.  Vietnam was a notable exception, implementing stringent control measures including quarantine, contact tracing, border controls, school closures, and traffic restrictions while case numbers were still low. A small number of island states, such as Samoa, Tonga and the Cook Islands, adopted an exclusion approach by largely closing their borders to incoming travellers.

By early March, the evidence base for elimination was growing, with the increasing realisation that COVID-19 is not pandemic influenza ⁵. A watershed moment was the report of the WHO joint mission to China, which confirmed that the pandemic there had been contained even after widespread community transmission had commenced ⁶. There was also strong evidence for the success of the elimination approach in Taiwan ⁷, Hong Kong, Singapore, and South Korea.

The concept of elimination is well-known to infectious disease epidemiologists ⁸. It refers to the absence of an infection in a country or region. While absence of disease is the ultimate goal, elimination criteria for highly infectious diseases such as measles allow for occasional outbreaks or imported cases provided they are stamped out within a defined time period ⁹. By contrast, eradication means that a disease has become extinct at the global level, at least outside laboratories.

There is no established definition for COVID-19 elimination.  Preliminary thinking suggests that such a definition would need to include a defined period of absence of new cases (perhaps 28 days, which is twice the maximum 14 day incubation period)¹⁰. This criterion would require a high-performing surveillance system and would exclude cases detected in arriving visitors while under quarantine ¹⁰.  At the time of writing in mid-May 2020, New Zealand had passed the acute phase of the pandemic response, and could be considered to be in a pre-elimination stage.  Case numbers were at low levels, with several days without new reports. Elimination status may take weeks or even months to achieve, and countries could potentially move in and out of this state depending on their success with containing the pandemic.

Benefits and costs of elimination

At the time New Zealand chose an elimination strategy, the exact nature of this response and its full justification had not been articulated². The health impact of a poorly contained pandemic had been modelled using a range of scenarios ¹¹,  demonstrating clear health gains if a widespread pandemic could be prevented in NZ. There was also a concern to avoid repeating the catastrophic impact of previous influenza pandemics on Māori and to protect neighbouring Pacific Islands ¹². 

The net economic benefits of an elimination strategy were uncertain and extremely difficult to estimate. An additional challenge was that both the pandemic and its response were likely to have a disproportionate impact on disadvantaged populations. While an elimination strategy had huge economic and social costs, the alternatives (counterfactuals) were almost certainly far more damaging. One advantage of an elimination strategy was that it provides a medium-term exit path for return to domestic economic activity without the constraints of circulating Sars-CoV-2 virus. Neither mitigation nor suppression provided a certain exit strategy, particularly given major uncertainties about coronavirus immunity and the potential for ongoing epidemic transmission for months to years under some scenarios ¹³. As with all COVID-19 strategies, the ultimate exit path will depend on developing effective vaccines and/or therapeutics.

Components of elimination and their implementation

Elimination requires an array of control measures tailored to local needs and to the transmission characteristics of the organism concerned. For COVID-19, the major components are similar to those used for pandemic control more generally. The main difference is the intensity and timing with which they are applied (see table). 

COVID-19 elimination requires a very strong emphasis on border management to keep the virus out.  That intervention would usually be combined with case and contact management to stamp out transmission, along with highly developed surveillance and testing to rapidly identify cases and outbreaks. If started early these measures may be sufficient for elimination without the need for lockdowns, as was achieved in Taiwan.

An elimination strategy requires highly functioning public health infrastructure. Increasingly, traditional approaches are supported by newer tools such as the use of digital technology to speed up contact tracing ¹⁴. Additional surveillance approaches can be used to provide increased assurance of elimination (eg, sentinel surveillance, sewage testing). However, even in the presence of a highly sophisticated surveillance system, transmission will continue to occur if isolation and quarantine adherence is suboptimal.

Table:  Components of pandemic control and features which distinguish the elimination strategy from mitigation and suppression

Barriers to successful elimination and how to overcome them

The COVID-19 pandemic was halted in China, demonstrating that there are no absolute biological barriers to its elimination ⁶. Having no important animal or environmental reservoirs is a necessary condition, and this appears to be the case for COVID-19 (though its actual origin in nature has not been determined so cases could in theory arise from this source). The combination of high infectiousness and presymptomatic transmission poses challenges for control¹⁵. Fortunately, its relatively long incubation period (about 5 days) makes contact tracing and quarantining effective, unlike influenza ⁵.

Changing human behaviour to reduce COVID-19 transmission is challenging for a virus that is as transmissible as COVID-19. That is why mandated extreme physical distancing and movement control (lockdown) may be needed. The intense lockdown carried out in New Zealand suppressed transmission and gave the country time to expand border controls, improve contact tracing, and undertake large-scale testing. Coming out of lockdown (which began progressively on 28 April) has to be managed carefully, as the goal is to emerge into a country that is free from community transmission (unlike the lockdowns in countries pursuing mitigation or suppression). Widespread use of face masks was not a feature of the New Zealand strategy but might in future reduce the need for this intervention ¹⁶.

Successful implementation of an elimination strategy requires early risk assessment, effective response planning, infrastructure, resources and political will. The global response to Sars-CoV-2 has been described as the ‘greatest science policy failure of our generation’ ¹⁷. An elimination strategy could potentially have been widely used to contain COVID-19 and protect populations in countries across the globe.

Conclusion and where to from here

New Zealand and Australia appear to have joined a small group of countries and jurisdictions pursuing an explicit, or implied, COVID-19 elimination goal, the others including mainland China, Hong Kong, Taiwan, Singapore, South Korea and a number of small island states and territories.  This set of countries is likely to expand in the future.  It is not hard to imagine travel between these countries being relaxed in the future once the risks are well understood and can be managed.  It may be time for these countries to actively share knowledge and evidence about the approaches that are supporting them to contain and eliminate COVID-19. 

There are multiple potential future scenarios. By pursuing and maintaining an elimination strategy, countries can prevent disease and death from COVID-19 and avoid further exacerbation of existing health inequities. They also move from having to manage ongoing pandemic transmission within their population to being able to make informed strategic choices about prevention and control options such as vaccines and antivirals as they become available.

References

1. New Zealand Government. New Zealand COVID-19 Alert Levels, 2020.
2. Baker M, Kvalsvig A, Verrall A, et al. New Zealand’s elimination strategy for the COVID-19 pandemic and what is required to make it work. New Zealand Medical Journal 2020;133(1512):10-14.
3. Ministry of Health. New Zealand Influenza Pandemic Plan. 2nd edition ed. Wellington: Ministry of Health, 2017.
4. Ferguson N, Laydon D, Nedjati Gilani G, et al. Report 9: Impact of non-pharmaceutical interventions (NPIs) to reduce COVID19 mortality and healthcare demand. 2020
5. Anderson RM, Heesterbeek H, Klinkenberg D, et al. How will country-based mitigation measures influence the course of the COVID-19 epidemic? Lancet 2020 doi: 10.1016/S0140-6736(20)30567-5
6. World Health Organization. Report of the WHO-China Joint Mission on Coronavirus Disease 2019 (COVID-19), 2020.
7. Wang CJ, Ng CY, Brook RH. Response to COVID-19 in Taiwan: Big Data Analytics, New Technology, and Proactive Testing. Jama 2020 doi: 10.1001/jama.2020.3151 [published Online First: 2020/03/04]
8. Dowdle WR. The principles of disease elimination and eradication. Bull World Health Organ 1998;76 Suppl 2:22-5.
9. Papania MJ, Orenstein WA. Defining and Assessing Measles Elimination Goals. The Journal of Infectious Diseases 2004;189(Supplement_1):S23-S26. doi: 10.1086/381556
10. Baker M, Wilson N, Hendy S, et al. The need for a robust scientific definition for the elimination of COVID-19 from New Zealand. Public Health Expert, 2020.
11. Wilson N, Telfar Barnard L, Kvalsvig A, et al. Potential Health Impacts from the COVID-19 Pandemic for New Zealand if Eradication Fails: Report to the NZ Ministry of Health. Wellington: University of Otago Wellington, 2020.
12. Wilson N, Barnard LT, Summers JA, et al. Differential mortality rates by ethnicity in 3 influenza pandemics over a century, New Zealand. Emerg Infect Dis 2012;18(1):71-77. doi: https://doi.org/10.3201/eid1801.110035
13. Kissler SM, Tedijanto C, Goldstein E, et al. Projecting the transmission dynamics of SARS-CoV-2 through the postpandemic period. Science (New York, NY) 2020 doi: 10.1126/science.abb5793 [published Online First: 2020/04/16]
14. Ferretti L, Wymant C, Kendall M, et al. Quantifying SARS-CoV-2 transmission suggests epidemic control with digital contact tracing. Science (New York, NY) 2020 doi: 10.1126/science.abb6936 [published Online First: 2020/04/03]
15. He X, Lau EHY, Wu P, et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. Nat Med 2020;26(5):672-75. doi: 10.1038/s41591-020-0869-5 [published Online First: 2020/04/17]
16. Goldstein G-P, Morgunov A, Nangalia V, et al. Universal Masking is Urgent in the COVID-19 Pandemic: SEIR and Agent Based Models, Empirical Validation, Policy Recommendations. 2020
17. Horton R. Coronavirus is the greatest global science policy failure in a generation. The Guardian 2020 9 April 2020.