In parts one and two of this series on pandemics, I took you on a journey into the world of zoonotic diseases, from the 14th century Black Death to modern day pandemics caused by zoonotic viruses. In the last part of this series, I will attempt to shed light on how pandemics come to an end. Just to offer a little light at the end of this long and dark Covid- 19 tunnel. 

Herd immunity

As a concept, herd immunity is incredibly controversial. In theory, it sounds appealing as it is a rapid way to end a pandemic. If the disease is allowed to spread uncontrolled and infect at least 60- 85% of a population, it can fizzle out as those people are now immune and the virus effectively runs out of people to infect. However, the human cost of such a strategy is humungous. In a country like India for example, nearly 800 million people would need to be infected. Considering India’s current death rate of 1.64 per 100 cases, this would translate to roughly 13 million deaths by the time herd immunity is reached. COVID- 19 is also a disease that is still being studied. There is no concrete evidence to indicate a sustained immune response, so there is no guarantee that herd immunity will result in a permanent eradication of COVID-19. Sweden was indirectly working towards herd immunity with their COVID-19 strategy. The jury is still out as to whether it was a success, or a moral and scientific failure.  


At the outset of a disease outbreak, the primary strategy is containment. This involves well developed public health measures such as isolating infected people, tracing their contacts, quarantining said contacts and extensive testing. These measures were brilliantly implemented by Taiwan, which did not need to enforce an economically debilitating lockdown. Instead, it shut its borders, hoarded personal protective equipment (PPE) and enacted the robust epidemiological methods mentioned above. Since the beginning of the pandemic, Taiwan has only registered 535 cases and 7 deaths (as of October 16th). It helps that Taiwan is a small country, whose vice president is the epidemiologist who effectively handled the SARS outbreak in 2003. On the contrary, countries that poorly executed containment measures due to a lack of preparation and rampant misinformation have suffered economic devastation from harsh lockdowns. Some like India allowed the pandemic to get out of control in spite of buying preparation time with one of the longest and most restrictive lockdowns in the world. Although, it should be noted that the case load and death toll in India would have been exponentially higher without the lockdown due to its large, densely packed population and poor rural healthcare facilities. 

SARS- CoV2 becomes endemic

Imagine a worst- case scenario wherein we do not find an effective vaccine against SARS-CoV2. What then? The answer can be found in the trajectory of the 1918 H1N1 influenza. Early 20th century doctors did not have access to modern medicine and virology. In the absence of therapeutics and vaccines, the disease spread like wildfire, infecting 500 million and killing 50-100 million people. Its march was only halted when enough people developed immunity. Once this occurred, the virus became endemic. It continued to circulate for the next 40 years as a seasonal flu, before being kicked out by the onset of the H2N2 influenza pandemic in 1957. To this day, we don’t know why one virus was able to effectively eliminate the other.  Unless there is extensive vaccination, it is likely that SARS-CoV2 will also become endemic. It might circulate seasonally like other endemic coronaviruses, but a combination of vaccination and natural immunity through infection will downgrade it from pandemic status. 


This is the most effective way out of a pandemic. This strategy worked brilliantly during the 2009 novel H1N1 avian influenza pandemic. Admittedly the virus was not as infectious as initially thought, but 6 months into the pandemic, scientists developed a vaccine. This slowed the spread and this version of H1N1 now simply circulates seasonally as the flu. Flu shots are given annually to reduce the number of infections from endemic influenza viruses. Unlike vaccines against diseases like small pox, which granted life- long immunity and helped eradicate the disease, the flu vaccine only offers temporary protection. This is because the virus, in a bid to survive, mutates rapidly and is able to evade the protection bestowed by vaccination. The hope is for a vaccine against SARS-CoV2 to behave more like the small pox vaccine rather than the flu vaccine, although the latter is more likely. Currently, there are 180 vaccines in development. Russia has authorised the use of its Sputnik V vaccine, but having skipped crucial phase three clinical trials before approval, it is being viewed with extreme scepticism. Their phase three trials are currently ongoing. The most high profile vaccine in phase three clinical trials (meaning that it is very close to the end of the testing phase) is being developed by the University of Oxford and AstraZeneca. This uses a weakened chimpanzee common cold virus that produces the same spike protein that is on the surface of the SARS- CoV2 virus. This has shown promising results in ongoing trials and the hope is for it to be rolled out to the public early next year. Although a safe and effective vaccine may be delivered within a staggeringly rapid timeframe, there are several questions that need answering. Firstly, it is unknown how many doses may be required. It is probable that at least two doses may be needed, which means a demand of 16 billion doses to vaccinate the entire world population. This raises questions about how many doses can be realistically produced immediately. AstraZeneca says it has the capacity to produce 3 billion doses and has signed an agreement with the Serum Institute in Pune, India to produce a further 100 million doses. There is also uncertainty around vaccine rollout. This encompasses questions such as: Who gets it first? Will poorer countries be able to buy approved vaccines? How affordable will it be for an average person? Hopefully world governments and the WHO can come up with answers and we can be vaccinated next year so that this nightmare can finally end. 

Featured image: The Conversation. https://www.inverse.com/mind-body/how-do-pandemics-end

Published by The Very Curious Biochemist

I am a protein biochemist by training, with a keen interest in new and fascinating science. I am passionate about communicating and discussing science and life as a scientist. As I belong to the rare species that actually enjoys writing, I thought I'd start this blog. I'm currently a postdoctoral scientist, so this really offers me an excellent distraction from the rigours of research. I hope you lovely visitors enjoy the material on offer!


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