In The Age of COVID-19: How Do Pandemics End?

By Chloe Teng

As we exceed the seven-month anniversary mark of the declaration of COVID-19 as a pandemic by the World Health Organisation (WHO), it is now increasingly confusing to understand what defines the “end” of such a global health crisis. On one hand, certain countries such as Brunei and Greenland have barely reported any new COVID-19 cases since March. They join a select group of 20 other nations who are currently categorised as very low risk, of which the Centres of Disease Control and Prevention (CDC) recommends no travel health notice for (CDC, 2020). Certainly, the perspective of their residents regarding the state of the pandemic would vary wildly from those in the United Kingdom and United States right now. If so, when, and most importantly, how do we reach a consensus defining the end of the COVID-19 pandemic?

The WHO, although responsible for determining the status of a disease, does not at the moment have a published set of criteria for how a pandemic could be considered to come to an end. One might therefore consider working backwards from the formal definition of a pandemic, which startlingly is not present as well. Instead, only descriptions of what constitutes a pandemic, along with definitions of pandemic phases exist. The WHO has long been criticised for this void in information, particularly regarding the declaration of the H1N1 influenza as a pandemic. The decision was also reflective only of the global dissemination of the H1N1 virus, and not of the severity of the disease. Ultimately, consequences for H1N1 were less serious than predicted, and public health responses to the 2009 pandemic were considered disproportionately aggressive in hindsight (Doshi, 2011). Even so, the issue remains contested in a sort of “chicken or the egg” paradox – Did the H1N1 pandemic resolve relatively peacefully due to the WHO’s classifications, or despite it? 

Seeing as there is a lack of official information to define the end of a pandemic, it seems logical to look to past outbreaks for an answer. One way that a pandemic could end is that the virus simply has no remaining hosts to infect. The Black Death of the 14th century, caused by the bacterium Yersinia pestis, was the deadliest pandemic in human history. Although recurrences were dated until the 19th century, the primary decline of cases were results of a high death rate that eliminated the population to an extent whereby infection from one person to another was no longer possible. Survivors also most often possessed a resistant genotype to the disease. Alternatively, those who recover from an infection may develop immunity. Even if lifelong immunity cannot be procured, which seems to be the case for SARS-CoV-2 and its reinfections, the length of the immunity needs only to outlast the rate at which the pathogen can infect organisms to survive. This is one of the reasons why herd immunity presents as a flawed strategy for COVID-19. The frequency of reinfection has not yet been proven due to insufficient data, thus uncontrolled transmission risks recurrent epidemics, especially if SARS-CoV-2 infections do not result in lasting protective immunity (Alwan et al., 2020).

Another way in which a pandemic could conclude is through environmental changes that disrupt the transmission of the pathogen. As living conditions in Europe improved, populations increasingly moved away from carriers of disease such as rats and fleas. A more direct example would be that of cholera. The emphasis on water sterilisation and purification came with the discovery by one of the fathers of modern epidemiology, John Snow, that a contaminated water pump was the source of a deadly cholera outbreak in London in 1854. By removing access to the water source, the outbreak was successfully controlled (History, 2017). Modern day strategies to control cholera and similar pathogen transmissions especially in developing countries are largely of the same vein.

To a certain extent, an extremely deadly pathogen is counter-productive for its own survival. That is why pandemics can end not by the eradication of the disease, but through mutations in the organism that lead to a decrease in virulence. By increasing transmission rates instead of disease severity, the pathogen can continue to survive in greater populations. In the lens of the COVID-19 pandemic, current trends indicate an increase in infectivity, and yet mortality rates have not followed suit. In vitro studies have proven that this is due to the D614G mutation, which is now the most predominantly identified variant in many regions of the world. By analysis of COVID-19 deaths in various geographical locations, researchers have shown that the D614G strain has a 23% higher reproduction number than the original G614 strain (Leung et al., 2020). However, this should not be regarded as the most optimal ending to our current crisis. The long-term effects of SARS-CoV-2 have yet to be investigated, and each individual can present varying severities of symptoms despite being infected by a comparatively milder strain.  

Finally, and perhaps the most popular ending envisioned for the current pandemic, is the implementation of an effective vaccine or therapy. The eradication of smallpox famously stemmed from the invention of the first ever vaccine by Edward Jenning. However, the complete elimination of the Variola major virus required systematic collaborative efforts, only being declared as eradicated in 1980 by the WHO, nearly 230 years after the vaccine was conceived. At the moment, 11 vaccines for SARS-CoV-2 are undergoing Phase 3 trials (WHO, 2020). Even so, the rush to develop a vaccine for the current pandemic has raised many concerns. Although the WHO recommends a minimum of 50% efficacy, other organisations like the United States Food and Drug Administration (FDA) have expressed consideration to approve vaccines that decrease disease severity rather than provide protection (BMJ, 2020). These factors, combined with the difficulty in ensuring equal global levels of vaccinated individuals, result in many questioning whether this will be what spells the end for the COVID-19 pandemic.  

Even with the wealth of historical information to draw on as we face our generation’s largest pandemic, it is difficult for even the most experienced of scientific experts to predict what comes next. As mainstream media latches onto a new projected ending for COVID-19 every day, it is vital for us to deny our human nature of finding the simplest of solutions in everything, and to acknowledge that what we are facing is a far more complex challenge that requires us to tackle it from multiple angles. We must further be prepared to embrace a future whereby we live alongside the SARS-CoV-2 virus perhaps in an endemic form, and that the end of COVID-19 may solely be referring to its pandemic status, and not its existence.

References:

Alwan, N., Burgess, A. B., Ashworth, S., Beale, R., Bhadelia, N., Bogaert, D., Dowd, J., Eckerle, I., Goldman, L. R., Greenhalgh, T., Gurdasani, D., Hamdy, A., Hanage, W. P., Hodcroft, E. B., Hyde, Z., Kellam, P., Kelly-Irving, M., Krammer, F., Lipsitch, M., McNally, A., McKee, M., Nouri, A., Pimenta, D., Priesemann, V., Rutter, H., Silver, J., Sridhar, D., Swanton, C., Walensky, R. P., Yamey, G. & Ziauddeen, H. Scientific consensus on the COVID-19 pandemic: we need to act now. The Lancet. 2020. DOI: 10.1016/S0140-6736(20)32153-X

Centres for Disease Control and Prevention. 2020. COVID-19 Travel Recommendations by Destination. Available from: cdc.gov/coronavirus/2019-nov/travelers/map-and-travel-notices.html [Accessed 28th October 2020]

Doshi, P. The elusive definition of pandemic influenza. Bulletin of the World Health Organisation. 2011 Jul 1;89(7):532-8. DOI: 10.2471/BLT.11.086173

History. 2017. Cholera. Available from: www.history.com/topics/inventions/history-of-cholera [Accessed 28th October 2020]

Leung, K., Pei, Y., Leung, G. M., Lam, T. T. Y. & Wu, J. T. Empirical transmission advantage of the D614G mutant strain of SARS-CoV-2. medRxiv. 2020. DOI: 10.1101/2020.09.22.20199810

Torreele, E. The rush to create a covid-19 vaccine may do more harm than good. BMJ. 2020;370:m3209. DOI: 10.1136/bmj.m3209

World Health Organisation. 2020. Draft landscape of COVID-19 candidate vaccines. Available from: who.int/publications/m/item/draft-landscape-of-covid-19-candidate vaccines [Accessed 28th October 2020]

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