The meaning of elimination of Covid-19

Critical to the success of New Zealand’s elimination strategy of Covid-19 community transmission has been the quality of expert advice of the country’s epidemiologists. They haven’t been the only medical specialists or other scientists to provide this expert advice but they have been at the forefront.

Before Covid-19 emerged as a pandemic many New Zealanders would have had little idea what an epidemiologist was compared with other specialist branches of medicine such as surgery, psychiatry, paediatrics and radiology.

As a cornerstone of the specialist branch of medicine called ‘public health’, epidemiology doesn’t involve the treatment of patients. Public health is about the health of populations rather than the treatment of individual patients.

Within public health, epidemiology studies and analyses the distribution, patterns and determinants of health and disease conditions in defined populations. Epidemiology shapes policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive healthcare.

Epidemiology influence

After initial but understandable uncertainty, epidemiologists quickly became central to the New Zealand government grasping the important of adopting the elimination strategy. At a time when government was looking to Europe, which was adopting various forms of mitigation, our epidemiologists were looking to Asia, particularly China, where the virus had hit earliest and where encouraging developments were emerging as a result of adopting the elimination.

The effect of their advice being accepted and adopted by government was the difference between having only twenty-six instead of thousands of Covid deaths (it was a narrow escape). There are several indicators to assess the effectiveness of the elimination strategy but, for me, humanness means that mortality rates trump the totality of the others.

Elimination isn’t eradication

Now two of our leading epidemiologists, Emeritus Professor David Skegg and Professor Philip Hill, (both at the University of Otago), have had published an article in the prestigious British Medical Journal This considered piece of writing discusses why elimination of community transmission of Covid-19 is achievable but emphasises that it should not be confused with eradication.

They note that many people confuse elimination with eradication. Giving small pox as an example, they clarify that eradication normally means permanent reduction to zero of the worldwide incidence of an infection. In contrast, elimination is the “maximum action” necessary to control the virus and stop community transmission “as quickly as possible.” It is acknowledged that some community transmission will occur after importation but steps would be taken to extinguish it.

The difficulty is that confusing eradication and elimination helps make the idea of eliminating Covid-19 community transmission seems impossible and therefore not worth pursuing.

Skegg and Hill acknowledge that elimination of an infection is often interpreted as the reduction of incidence to zero in a defined geographical area. This is wrong. Instead, using tuberculosis and measles as examples, elimination should be defined as reduction of case transmission to a predetermined very low level. So far, unlike tuberculosis and measles, there is no internationally agreed specific numeric definition for the elimination of Covid-19. This is unsurprising given the uniqueness of the pandemic.

They warn of the serious risks to populations, health systems and economies of not aiming for elimination, including driving the emergence of new variants that are resistant to current vaccines (even where there are higher vaccination rates).

Skegg and Hill also debunk the false dichotomy alleged between elimination and economic performance. They observe that countries pursuing an elimination strategy have experienced less disruption and economic damage than those that have focused on mitigation as confirmed by a comparative study by the Organisation for Economic Cooperation and Development. New Zealand and China are prime examples of successful elimination countries although they are not singled out in their article.

Advancing elimination globally

The authors make a good call for ambition and leadership from political leaders noting that the emergence of more transmissible variants presents challenges for controlling the virus by conventional public health measures. But, when reinforced by highly effective vaccines (current problems of global scarcity and inequitable distribution are recognised) it is feasible. But this requires that an “unduly strict interpretation of elimination” does not “discourage countries from adopting this ambitious approach.”

To advance this direction the epidemiologists recommend that the World Health Organisation accept the advice of the Independent Panel for Pandemic Preparedness and Response to develop a road map to guide efforts to promote a realistic definition of elimination. In their words this would “…encourage ambition, rather than defeatism, in confronting the coronavirus causing such havoc around the globe.”

The luck of Aotearoa

Professors Skegg and Hill are advocating a much needed global strategy to ensure the elimination of community transmission of Covid-19. To begin with it will require WHO to step up rather than be ambivalent.

New Zealand is fortunate that its government has had the wisdom to appoint both professors to an expert committee established to advise on our own road map looking ahead (with Skegg as its chair). For much of last year epidemiologists and other experts were restricted to a frustrating reactive role in their relationship with the Ministry of Health.

This committee has a direct report line to the Minister of Health. It represents an important shift to a proactive role which hopefully is going to be recognised in its report expected later this week.

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