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Eradication, elimination, suppression: let’s understand what they mean before debating our course

by Anita Heywood, Associate Professor, UNSW and C Raina MacIntyre, Professor of Global Biosecurity, NHMRC Principal Research Fellow, Head, Biosecurity Program, Kirby Institute, UNSW First published in The Conversation The current surge in community transmission of COVID-19 in Victoria has brought renewed discussion of whether Australia should maintain its current “suppression” strategy, or pursue an “elimination” strategy instead.

But what do these terms actually mean, and what are the differences between the two?

Read more: As restrictions ease, here are 5 crucial ways for Australia to stay safely on top of COVID-19

In theory

Disease eradication means a global absence of the pathogen (except in laboratories). We achieved this for smallpox in 1980. Diseases suitable for eradication are usually those where humans are the only host, and where there’s an effective vaccine or other prevention strategy.

Disease elimination relates to a country or a region, and is usually defined as the absence of ongoing community (endemic) transmission.

Elimination generally sits in the context of a global eradication goal. The World Health Organisation sets a goal for eradication, and countries play their part by first achieving country-wide elimination.

Cases and small outbreaks may still occur once a disease is eliminated — imported through travel — but these don’t lead to sustained community transmission.

Finally, disease control refers to deliberate efforts to reduce the number of cases to a locally acceptable level, but community transmission may still occur. Australia’s current suppression strategy, though seeking to quash community transmission, can be classified as disease control.

In practice

Elimination and suppression strategies employ the same control measures. For COVID-19, these include:

  • rapid identification and isolation of cases

  • timely and comprehensive contact tracing

  • testing and quarantining of contacts

  • varying degrees of social distancing (lockdown, banning mass gatherings, keeping 1.5m distance from others)

  • border controls: restricting entry through travel bans, and quarantine of returning international travellers

  • face masks to reduce transmission.

Read more: Grattan on Friday: Does Victoria's second wave suggest we should debate an elimination strategy?

The differences between a suppression strategy and an elimination strategy are the strictness, timing, and duration with which these measures are applied, especially travel restrictions.

For example, under a suppression strategy, physical distancing requirements might be lifted while there’s still a low level of community transmission. But under an elimination strategy, these measures would remain in place until there’s no detectable community transmission.

What’s realistic for COVID-19?

First, the prospect of eradicating COVID-19 is likely no longer feasible, even with a vaccine.

People without symptoms may be able to spread COVID-19, which makes it difficult to identify every infectious case (SARS, for example, was only spread by people with symptoms). And if the virus has an animal host, animal reservoirs would also need to be eradicated.

There are subtle differences between disease control, elimination, and suppression

So what about elimination?

For measles, elimination is defined as the absence of endemic measles transmission for more than 12 months. Countries must demonstrate low incidence, high quality surveillance and high population immunity.

Imported cases in unvaccinated returning travellers and occasional small outbreaks continue to occur, but a country will lose its elimination status if community spread lasts longer than one year.

The majority of the Australian population are immune to measles, which lowers the probability of sustained outbreaks. But most Australians remain susceptible to COVID-19.

So future sustained outbreaks, like the current Victorian outbreak, will remain possible until we can vaccinate the population — even under an elimination strategy.

Read more: Lockdown, relax, repeat: how cities across the globe are going back to coronavirus restrictions

Like we have with measles, for COVID-19, we need a definition of elimination with specific criteria that can be measured.

Declaring COVID-19 “eliminated” after the absence of community transmission for a few weeks means little during a pandemic, and may lead to complacency in the community. This period should be more like a few months.