PANDEMIC
The Impact of Herd Immunity v.s. Suppression on the Spread of COVID-19 By Rachel Kienle, Biochemistry Major. 2023
T
he 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 infection-
4
derived 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
