A pandemic is a new outbreak of an infectious disease that affects a significant number of people in most countries around the world. There are several different possibilities for what happens afterwards.


If we could stop all COVID-19 infections around the world then the virus would be eradicated. Unfortunately, eradication is incredibly difficult, and historically we have only successfully eradicated two diseases, smallpox and the cattle disease, rinderpest.

If, however, all COVID-19 infections were stopped at a local level (a country or even a community) then we would say the disease in those regions was eliminated. The virus would still be present globally, but there would no longer be any cases within the region. If eradication or elimination are not achieved, but cases are dramatically reduced, then the virus could become sporadic, with occasional infections occurring at low levels.

But what happens if virus transmission continues as it currently is in the UK (with 88,376 new cases as of 16 December 2021)? At some indeterminate point the pandemic would no longer be a new outbreak but would instead become an endemic, where there are regular high rates of the disease that may even be comparable in number to the rates seen during the pandemic phase.

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While there is no defined point in time whereby a pandemic becomes an endemic, it tends to occur when case numbers stabilise over an extended period of time. One example of a virus that caused a pandemic and now is responsible for a global endemic is HIV, the virus that causes AIDS. Thus, the term we use for describing the current state of COVID-19 infections in a country is guided by the number of cases, the duration the disease has been circulating and the stability of case numbers over time.

The level of cases we see in the UK will be driven by our public health choices. As we have seen from countries like New Zealand, eliminating COVID-19 transmission is possible and would allow the removal of most mitigation measures; however, the risk of resurgence of the virus from other countries requires continual surveillance and public health readiness.

In contrast, other countries have removed most or all of their mitigation measures with the aim of living with the virus. This continued virus circulation risks overburdening health systems (perhaps necessitating new mitigation measures) while causing significant health impacts to those infected. There are also additional long-term impacts, as it’s estimated that nearly 14 per cent of COVID-19 infections result in symptoms lasting three months or longer, known as long COVID.

In between these two extremes are low-level endemicity or sporadic infections. Some viruses that we regularly hear about fall into this category (for example, the measles virus causes sporadic infections in the UK). With COVID-19 at a low endemic or sporadic level, and with high vaccination rates, mitigation measures would not be needed for most of the population. Instead, public health teams would need to investigate and contain any outbreaks at a local level, just as is done with measles.

We have made significant progress in reducing COVID-19 hospitalisations and fatalities; however, case numbers are still high in the UK and in many areas around the world. In addition, many people in the UK remain at risk of COVID-19 disease due to being unvaccinated, being ineligible to be vaccinated (too young to receive the vaccine), or being clinical vulnerable. Because of this, there are significant risks
of allowing for high-level endemic COVID-19 disease.

Our actions over the coming months can help drive down new infections while increasing coronavirus vaccine coverage, potentially enabling the elimination of COVID-19 or the transition to a sporadic or low-level endemic disease, reducing the long-term burden on the NHS. This would protect health and wellbeing while minimising long-term need for population-level mitigation measures.

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Jeremy Rossman is a Senior Lecturer in Virology and President of Research-Aid Networks, University of Kent. His research focuses on the process of infectious disease outbreaks, and he has contributed to studies published in journals including PLoS Pathogens, Bioinformatics and Cell.