How to eradicate a virus

January 18, 2022

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At the beginning of 2020, our entire world got shocked by the new coronavirus SARS-CoV-2.  Now almost two years later we have realised that we will never get rid of this coronavirus and that we have to learn to live with the virus. However, at the beginning of the pandemic, most governments communicated another approach. They were convinced that by the use of measures, such as lockdowns and vaccination, we would get rid of this virus. But is it even possible to get completely rid of a virus? And if it is possible, how should we approach this and what can we learn from the past?

Smallpox

Before any measures or vaccination, every person who contracted the coronavirus would spread the virus to approximately two or three people. On average, 1 out of every 200 people who got the virus died because of it [1]. Now two years later this has resulted in over 300 million cases of which more than 5,5 million had a fatal ending [2]. Now imagine what the impact would have been if this virus was two to three times as contagious and more than 50 times as deadly, this virus is called smallpox.

Smallpox has been around for at least 3000 years and has even been found on Egyptian mummies [3]. When a person contracts smallpox it will experience symptoms like vomiting, fever, and a skin rash which turn into fluid-filled blisters in a matter of days [4]. An infected person would on average spread the virus to 6 people and an infected person would have a 30% probability of dying. This is even higher for babies [5]. As one can expect, this virus tormented humanity for thousands of years, leading to an estimated 300 million casualties in the 20th century alone [6].  Luckily for us, we no longer have to worry about this virus because in 1980 the virus had been completely eradicated from the entire globe [3].

Eradication

When attempting to eradicate a virus, many disciplines and people have to work together in perfect harmony, because just one infected person could lead to an entire new outbreak. There are many factors that can tell you something about whether a virus is eradicable or not, these can be summarized in the following three pillars:

  • Vaccination
  • Transmission
  • Global cooperation

Vaccination

For a virus to be eradicated there has to occur some form of group immunisation, to stop the virus from spreading. This can happen through contagion, making you immune for some time after infection, or through vaccination, making you less susceptible or completely immune for some time after vaccination. Since natural immunisation through infection takes too long, vaccines have to be used to eradicate a virus.

The first vaccine ever was created in 1796 by the English doctor Edward Jenner. He noticed that milkmaids that had contracted the cowpox virus, a virus not dangerous for humans, became immune from smallpox. He then used this cowpox vaccine to create a vaccine for smallpox.  In the second half of the 20th century, this vaccine had been improved such that it would give full immunity for at least 3 to 5 years [3]. This full immunity for multiple years is one of the key conditions that have to be met for a virus to be eradicable, if this condition is not met then there will be vaccinated people that still contract the virus, causing it to keep spreading under the population.

Transmission

Many viruses that we know are able to spread through animals. For example, the malaria virus is mainly transported by mosquitos and Ebola can spread to humans from bats and other animals. To fully eradicate these viruses, even vaccinating every person on the globe might not be enough, as this virus can continue to live in other animals and can re-enter the human population once the immunity of the vaccination wears of. The smallpox virus, however, is only transmissible from one human to another, hence vaccination eliminates the only way this virus can spread [1].

Another advantage that smallpox has, for eradication, over other viruses is that a person infected with smallpox is only contagious when this person is experiencing symptoms. This makes it easier to isolate a contagious individual or to vaccinate the people around the contagious person before this person infects too many others [1]. The fact that the symptoms caused by smallpox are very early and easily observable also helps in isolating and/or vaccinating early, to stop further spreading [4].

Global cooperation

Once it has been established that the existing vaccines are good enough to fully stop the transmission of a virus, there is a very well-communicated global vaccination campaign necessary to make sure people in every corner of the globe can be vaccinated. At the start of the 20th century most western countries had nearly wiped out smallpox, but countries with fewer resources, worse healthcare and infrastructure, and civil unrest were still tormented by smallpox [1].

In 1967 the World Health Organisation (WHO) started the Intensified Eradication Program, with the main goal to fully eradicate smallpox [3]. This program funded many laboratories in countries where smallpox occurred regularly, such that these countries could produce their own vaccines and also greatly invested in the equipment needed to vaccinate people in very remote regions [3]. The initial tactic of this program was to just vaccinate everyone, but in denser populated it was harder to track outbreaks, causing the virus to still spread quickly. This caused the WHO to switch to a more targeted approach, called ring-vaccination. Instead of randomly vaccinating all people in a region, priority was given to anyone who had been in contact with or lived nearby an infected person. This way the vaccinated people formed a barrier between the infected person and the rest of the population limiting further spreading of the virus [1]. This change in tactic was the final push needed and on May 8th, 1980 the WHO declared smallpox eradicated [3].

Coronavirus

Up until now, smallpox has been the only virus that has ever been eradicated by humans, but there are some other candidate viruses that theoretically could be eradicated, like polio or the Guinea worm disease [1]. Unfortunately, this is not the case for the current coronavirus SARS-CoV-2.

When the new mRNA vaccines were made they showed extremely high effectiveness of around 98% [7]. Unfortunately, new variants arose leading to a decrease in effectiveness, being just 37% for the currently dominant Omicron variant [8]. The immunity provided by vaccines or through infection also seems to last for less than a year [9]. When looking at transmission, we know infected people can already be contagious before they show any sign of symptoms, making it very hard to isolate people in time to prevent the virus from spreading [10]. This combination of the quality of the vaccines and the way the virus spreads cause the current coronavirus to not be suitable for eradication and thus we have to learn to live with the virus.

Sources

[1] https://www.vox.com/future-perfect/21493812/smallpox-eradication-vaccines-infectious-disease-covid-19

[2] https://www.worldometers.info/coronavirus/

[3] https://www.cdc.gov/smallpox/history/history.html

[4] https://www.cdc.gov/smallpox/symptoms/index.html

[5] https://www.cdc.gov/smallpox/about/index.html

[6] Koprowski H, Oldstone MB (1996). Microbe hunters, then and now. Medi-Ed Press. p. 23.

[7] Bruxvoort K. J. et al. (2021). Effectiveness of mRNA-1273 against delta, mu, and other merging variants of SARS-CoV-2: test negative case-control study

[8] Sarah A. Buchan, et al. (2022). Effectiveness of COVID-19 vaccines against Omicron or Delta infection.

[9] https://www.yalemedicine.org/news/how-long-will-coronavirus-vaccine-last#:~:text=Pfizer%20and%20Moderna%20have%20been,at%20the%20six%2Dmonth%20mark.

[10] https://www.health.harvard.edu/diseases-and-conditions/if-youve-been-exposed-to-the-coronavirus


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