The Impact of Herd Immunity v.s. Suppression on the Spread of COVID-19

By Rachel Kienle, Biochemistry Major. 2023

The novel coronavirus first emerged in late 2019 from the Wuhan Province of China and was declared a global pandemic by the World Health Organization on March 11, 2020.1

Suddenly, across the globe, countries were faced with the task of creating plans to protect both the citizens and economies of their countries. Most countries chose either an infection-derived herd immunity approach (rather than vaccination-derived herd immunity) or suppression of the virus by using social distancing and prevention strategies. Many details about the virus, such as the duration, nature, and effectiveness of any immunity resulting from COVID-19 infection, are still unknown today. This causes uncertainty in the effectiveness of protecting the lives of citizens for both strategies.2 As time has gone on since the initial spread of the virus, it has been shown that the national governments of the countries using the suppression strategy have lowered the numbers of cases and casualties in their countries compared to those using relatively controlled infection to gain herd immunity.

Herd immunity occurs when enough people obtain antibodies through natural exposure to the virus or vaccination in order to provide protection against the virus. Approximately 60-70% of the world’s population would have to develop immunity to achieve herd immunity.5 The United Kingdom’s first COVID-19 plan was to create an infection-derived herd immunity by permitting the infection of a large proportion of their population without exceeding health care capacity.2 However, a study published in October 2020 simulated how achieving an infection-derived herd immunity without overwhelming hospitals with huge amounts of infected citizens would be challenging, leaving a small margin for error.4 If preventative measures were not taken and natural infection continued, then 77% of the United Kingdom’s population would be infected. The graphs D, F, and E from Figure 1 show that the total population exposed and the number of deaths decline with social distancing measures. For the United Kingdom to effectively create an infectionderived herd immunity the hospital capacities would have to be exponentially increased.4 Finally, on March 16, 2020, the British government changed its initial strategy and went into a preliminary lockdown following suppression strategies.5

Figure 1. An age-structured Susceptible Exposed Infectious Recovered (SEIR) model to demonstrate stimulated examples of SARS-CoV-2 spread in the United Kingdom.

Adapted directly from Brett and Rohani 2020.

Similarly, Sweden used an infection-derived herd immunity since COVID-19 first reached the nation. The approach aimed to protect the elderly and those with preexisting conditions while the rest of the country lives a semi-normal life.5 However, approximately “three times more people died from COVID-19 in Sweden (2,679 deaths per 10 million inhabitants) compared to Germany (6,848 deaths per 80 million inhabitants)”5 .

Although Sweden has a higher amount of single households and sparser populations outside the metropolitan area and thus a higher advantage to fight the virus compared to Germany, the statistics showed that Germany had a higher success rate because the country used suppression strategies.5 Even with a higher chance of success at herd immunity compared to other countries, the strategy faces other challenges as well. It is unclear how long antibodies provide immunity and combined with the long-term impacts of having the disease, makes infection-derived herd immunity a risky endeavor.5 As shown by the greater rate of deaths in Sweden compared to countries that used suppression, it has not shown to be the best strategy to save the maximum amount of lives.

Figure 2. Graphs depicting prospects of achieving herd immunity.

Adapted directly from Brett and Rohani 2020.

Suppression is the other main strategy used by countries to manage and contain the spread of COVID-19. The goal of suppression through nonpharmaceutical methods is to reduce the transmission of the virus so that it is no longer considered a threat. After suppression is accomplished, countries can move their efforts towards stopping the reintroduction of the virus back into the population.4

An example of a country that has so far been able to successfully use suppression techniques to reach a near-zero percent incidence rate of COVID-19 is New Zealand. Non-pharmaceutical methods such as restriction of movement, physical distancing, enhanced hygiene practices, and governmental case tracking and thereafter management have given New Zealand the ability to maintain near-zero COVID-19 cases. These methods are similar to those that have been used in Asian countries such as China, Singapore, and South Korea. With its island setting and citizens’ high income, New Zealand has been able to better contain the spread of the virus.6

Countries such as Sweden that have used herd immunity as their strategy to combat COVID-19 have not been able to save as much of their population as countries that use suppression strategies like New Zealand. Although it can negatively impact the economy and the everyday life of a country’s citizens is upturned in a complete shutdown, nearzero cases in New Zealand have shown that it is the most effective way to stop the spread of the virus. approximately “three times more people died from COVID-19 in Sweden (2,679 deaths per 10 million inhabitants) compared to Germany (6,848 deaths per 80 million inhabitants)”.5

Figure 3. Cumulative deaths of SARS COV-2 infected patients in Germany, Sweden (blue line), Germany (black line) and Taiwan.

Adapted from Jung et al, 2020.

[1] The Visual and Data Journalism Team. (2021, January 11). COVID-19 pandemic: Tracking the global coronavirus outbreak. BBC News.https://www.bbc.com/news/ world-51235105.

[2] Herd immunity is an impractical COVID-19 mitigation strategy, says study. (2020, September 23). European Pharmaceutical Review. https://www.europeanpharmaceuticalreview.com/ news/129061 herd-immunity-is an-impractical-COVID-19mitigation-strategy-says-study/

[3] Herd immunity is an impractical COVID-19 mitigation strategy, says study. (2020, September 23). European Pharmaceutical Review. https://www.europeanpharmaceuticalreview.com/ news/129061/herd-immunity-is an-impractical-COVID-19mitigation-strategy-says-study/.

[4] Brett, T. S., & Rohani, P. (2020). Transmission dynamics reveal the impracticality of COVID-19 herd immunity strategies. Proceedings of the National Academy of Sciences, 117(41), 25897–25903. https://doi.org/10.1073/pnas.2008087117.

[5] Jung, F., Krieger, V., Hufert, F. T., & Küpper, J.-H. (2020). Herd immunity or suppression strategy to combat COVID-19. Clinical Hemorheology and Microcirculation, 75(1), 13–17. https://doi.org/10.3233/ch-209006.

[6] Jefferies, S., French, N., Gilkison, C., Graham, G., Hope, V., Marshall, J., McElnay, C., McNeill, A., Muellner, P., Paine, S., Prasad, N., Scott, J., Sherwood, J., Yang, L., & Priest, P. (2020). COVID-19 in New Zealand and the impact of the national response: a descriptive epidemiological study. The Lancet Public Health, 5(11), e612–e623. https://doi. org/10.1016/s2468-2667(20)30225-5.