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Update on Global Immunity to Covid-19: Retrospective Review of Sweden’s Approach to the Pandemic

Posted on: July 12, 2022

Back in June 2020, FlowMetric published a blog outlining the path to global herd immunity against Covid-19. At the time there were no vaccines available other than within clinical trials, and most of the world was taking a lock-down approach to tackle the spread of the virus. The exception was Sweden, whose government took the tactic of warning their population of the risks of the virus but allowing schools and businesses to remain open and life to continue near normal without any mandates. Experts debated whether this approach, led by Sweden’s Chief Epidemiologist, Anders Tegnell, was genius or a disaster in the making. Although never expressed publicly, Tegnell’s goal was to achieve herd immunity within the Swedish population as soon as possible- and in the absence of a vaccine, to him and many in Sweden who agreed with this alternative narrative, this was a risk worth taking. Now, with the perspective of hindsight and serological testing to assess immunity, many in the scientific community are asking, was Sweden’s approach the right one after all? It’s a more complicated question than it seems at first since there are several factors and considerations contributing to perceived success or failure. In this blog, we review some of the key decisions that shaped Sweden’s pandemic response, and emerging data on the impact of Covid-19 in Sweden compared to other European countries.

The Goal of Herd Immunity

It was clear early in 2020, that Sweden’s Covid-19 infection and death rates were the highest in Europe, and while the rest of the world went into some form of lockdown, life in Sweden continued relatively unphased by the emerging Covid-19 pandemic. No mandates were put in place, and the onus was on individuals to determine their risk and act accordingly. Many neighboring countries were outraged by Sweden’s approach, but if establishing herd immunity was the goal, it was to come at a great price to Sweden’s most vulnerable populations.

Herd immunity, otherwise known as population immunity, represents the indirect protection from an infectious disease when a certain percentage of the population is immune through either infection or vaccination. By Fall, 2020, the WHO announced that herd immunity to Covid-19 should be achieved by protecting populations through vaccination and not by exposing them to the pathogen that causes the disease, quote ‘Never in the history of public health has herd immunity been used as a strategy for responding to an outbreak, let alone a pandemic. (ref. WHO Director-General’s opening remarks, media briefing Oct. 12th, 2020).

Use of Face Masks

One major factor contributing to the high numbers of infections within the Swedish population during the early months of the pandemic was the lax approach to the use of face masks and social distancing. In fact, the wearing of facemasks was actively discouraged to help mitigate fear within the general population (Bjorklund and Ewing, 2020), and their use was recommended only in hospitals by June 2020 after more than 5000 deaths (Sörensen, 2020). It was a strange decision based on the data supporting the airborne nature of the virus, but the Swedish government saw this as another personal decision for its population. This most likely contributed heavily to the initial wave of infections represented in Fig 1. showing Sweden’s high death rates by June 2020, compared with neighboring countries.

June 2020

June 2021

Figure 1. Map of Infection Rates and Deaths per million- Comparisons with neighboring countries including Norway and Denmark who took very different approaches to lockdown and restrictions to manage the pandemic. By June 2020, Sweden’s rates of infection were the highest in Europe. By the following year, the reverse is observed, with higher infection rates reported across most of Europe.

Figure 2. Cumulative confirmed Covid-19 deaths per million people. Due to varying protocols and challenges in the attraction of the cause of death, the number of confirmed deaths may not accurately represent the true number of deaths caused by Covid-19. If Sweden’s death rate was the same as neighboring Denmark, then then it would have suffered only 4,429 deaths from Covid-19, compared with >18,500 currently reported. In contrast, the USA and UK death rates were the highest in the developed world, even with severe lockdowns.

Social Distancing

Although social distancing was encouraged even early on during the pandemic, there were no strict travel mandates and many Swedish families traveled to neighboring countries to go skiing during the February 2020 school break; on March 7th, 2020, more than 30,000 Swedes traveled to Stockholm to attend the final of the European Song Contest. Both activities likely triggered so-called ‘super-spreader’ events contributing to the first wave of infection across Sweden and sadly also to its’ neighboring countries. Sweden only eventually banned public gatherings of greater than 500 once the death toll was over 5000, and then to less than 50 by the end of the year. The exception was for those over 70 years of age, who were encouraged to remain socially distant and visitations to retirement homes banned by the end of March 2020 (Tegnell 2021). However, by this point, Covid-19 was rampant within retirement homes, leading to high infection rates in the residents and the staff who were caring for them.

ICU and Healthcare Resources

Sweden has a relatively low number of hospital beds and intensive care unit beds per capita (2.2 per 1000; and 5.8 per 100,000 people) respectively compared with other EU countries. This most likely contributed to the policies crafted by the Swedish government which prioritized resources based on patient age and overall health based on BMI. However, even within hospitals, insufficient PPE was available, and testing took a significant time to ramp up to meet requirements (Regioner med färre sjuka bör "stoppa smittan". Västerbottens–Kuriren (in Swedish). 2 June 2020). Field hospitals were established in Gothenburg and Helsingborg to expand ICU and hospital resources across the country, but the Gothenburg ICU site soon closed due to a lack of protective standards for both patients and healthcare workers.


Sweden’s government eventually acknowledged that it had misread the Covid-19 risk to the elderly and as a result had experienced huge losses within retirement homes. There was also a questionable approach to the care of elderly patients, with very few of these patients admitted to a hospital. Instead, many elderly Covid-19 patients were administered morphine (rather than potentially life-saving oxygen) in place of hospitalization, and in most instances, this took place without family notification. The mindset was that these patients were unlikely to recover, and therefore minimal resources should be applied to this segment of the population (Vogel, 2020). By November 2020 the Swedish Health and Social Care Inspectorate, the government agency responsible for supervising resources within healthcare and social services was forced to acknowledge widespread, systemic failures in the care of the elderly population, however even today, no one agency has been held responsible (Bjorklund and Ewing, 2020).

Children and Young Adults

Early on during the pandemic, the Swedish government incorrectly claimed that children could not become sick with Covid-19 and that they played a negligible role in transmission. Initially, all schools and daycare centers were kept open with minimal to no disruption, but by March 2020 upper secondary schools and universities transferred to online classes. However, with little to no Covid-19 testing available to children, the real impact of this strategy on the spread of Covid-19 within the population may never be fully understood. Retrospective studies have identified more than 100 cases of multisystem inflammatory syndrome (MIS-C) after contracting Covid-19 in Swedish children (published in Xinhuanet, Editor Huaxia, May 2022; Editor’s note NEJM Jan. 2021). This is a markedly higher number than all neighboring Scandinavian countries who have identified on average <10 cases each (Vogel, 2020b), indicating that Covid-19 cases in Swedish children were several-fold higher than in neighboring countries that imposed more rigorous lockdown strategies for their younger populations.

In October 2021, a first-of-its-kind study was published by Bjorkander et. al. outlining a population-based study of humoral and cellular immunity to SARS-CoV-2 in young, unvaccinated Swedish adults. This study provided strong evidence that this population should be considered major spreaders of Covid-19. The study’s seroconversion data is summarized in Figure 3. One in four participants were SARS-CoV-2 seropositive, and typically associated with a household reporting Covid-19 disease and correlating with memory B- and T-cell responses. Tracking over time, revealed that seropositive numbers remained stable from October to December 2020, then increased to over 30% in January 2021, and by the summer of 2021, these rates had peaked at 40% but were predominantly associated with IgM+ and therefore the result of more recent infections. Since then, Sweden has become one of the few countries that are offering T-cell testing of immunity to its population to assess protection from (re)infection. This type of testing may be critical in the long run to understanding the value of vaccination and the timing of boosters (Ameratunga et. al. 2021).

So, with such high seroconversion rates, why isn’t the Swedish population immunoprotected from Covid-19? The Bjorkander study and other similar serology studies have outlined the surprisingly rapid decay of anti-SARS-CoV2 antibodies associated with mild Covid-19 symptoms, highlighting the need for vaccines in the long run (Ibarrondo et. al. 2020). But in addition to this, a study by Juliette Pulliam’s team based in South Africa, a country with one of the highest seroconversion rates globally, has shown high reinfection rates within the population coinciding with the emergence of new variants of SARS-CoV-2. Some individuals were found to have been reinfected up to 4 times within a 12-month period, as new the Delta and Omicron variants emerged within the population. This reinforced an earlier study in the UK, that had identified that the Delta variant has a higher risk of reinfection compared with the alpha (Public Health England, “SARS-CoV-2 variants of concern and variants under investigation - Technical briefing 19, 2021, p. 55). These findings are surprising since laboratory-based neutralization assays indicate significant immune protection based on infection with an earlier variant (Alpha- Beta-, Delta-, to Omicron). Therefore, epidemiological surveillance such as the UK and South African studies are going to be critical in understanding how SARS-CoV-2 is transmitted in the real world.

Figure 3. SARS-CoV-2 anti-RBD IgM, IgA, and IgG prevalence and titers. (A) The proportions of SARS-CoV-2 seropositive and seronegative subjects. (B) The titers of SARS-CoV-2 anti-RBD IgM, IgA, and IgG in samples from historical controls collected before the pandemic (n = 108) and BAMSE participants (n = 980), expressed in arbitrary units, and the prevalence of IgM, IgA, and IgG displayed as pie charts for the BAMSE participants. (C) Venn diagram showing the overlap of IgM, IgA, and IgG seropositivity. (D) The percentages of IgM+, IgA+, and IgG+ subjects for each study month. The chi-square test was used for statistical analysis. Red lines indicate median values; green lines, assay cutoff values.

What is clear from all of this is that Sweden’s pandemic playbook was not followed. Sweden has a strong track record in pandemic preparedness, based largely on the World Health Organization guidelines 2017, and the Disease Prevention Act (2004:168). However, with the onset of the Covid-19 pandemic, no one agency or governing body, stepped up to make recommendations, but rather gathered data and passed almost all responsibility onto individual residents. This was coupled with deprioritized testing initiatives and the allocation of healthcare resources based on cost/risk benefits- i.e., rather than the precautionary approaches laid out in the pandemic playbook, there was a reliance on existing precedents, managed at arm’s length, in place of the rapid adoption of new policies.

This trend has continued over the past two years and in February 2022, the Swedish government halted all widespread testing for Covid-19, even among people displaying symptoms. "We have reached a point where the cost and relevance of the testing are no longer justifiable." Swedish Public Health Agency chief Karin Tegmark Wisell told the national broadcast SVT. All restrictions on gatherings were lifted and Swedes are seemingly accepting that the virus is endemic. In contrast, the UK is expanding access to home test kits, even offering free home delivery in the hope that personal responsibility will enable a return to normal social activities, and Greece is requiring teachers to test twice a week and requiring Covid-19 passports to enter restaurants.

Moving from Pandemic to Endemic

With the rollout of highly effective vaccines, there is a slowing in death rates and a significant decrease in the severity of Covid-19 symptoms associated with infection. However, there is little chance that vaccination will achieve the all-elusive herd immunity for Covid-19. Why? Well, herd immunity is a fluctuating and unsustainable target when it comes to viruses like SARS-CoV-2. It is based on the infectivity of the pathogen, its prevalence in the population, as well as the immunity of the population (from either infection or vaccination). Each emerging variant of the virus displays varying levels of virulence, higher than predicted reinfection rates, and different sectors of the population respond differently to infection or vaccination. We should therefore accept that Covid-19 is now endemic, and the responsible use of vaccines may be the only effective means of managing future outbreaks (Aschwanden, 2020).

Figure. 4. ECDC Covid-19 Vaccine tracker is available online at www.ecdc.europa.eu with monthly updates on vaccination rates across Europe.

Initial vaccination rates in Sweden have been one of the highest although booster vaccination rates are lagging behind other areas of Europe. Covid-19 infection rates in Sweden today are ~1% of the peak with ~18 infections per 100K people, which is one of the highest rates in Europe currently. Real-time updates are available on the Reuters Coronavirus Tracker.

Sweden: the latest coronavirus counts, charts and maps (reuters.com)

Final Thoughts

So, now in the third year of this pandemic, how does Sweden’s Covid-19 recovery compare to others? Well, it is complicated and there are many factors contributing to the effects of the pandemic within any given country. The first wave of infection was devastating, especially for the elderly population in Sweden (Olofsson, 2022). Neighboring countries such as Finland and Denmark instigated lockdowns and testing strategies with great effect to both flatten the curve of infection and protect the most vulnerable. This undoubtedly saved many lives and enabled precious healthcare resources to be more effectively implemented. In Sweden, healthcare resources were prioritized based on the perceived risk of a poor outcome, and this impacted the survival rates within the most vulnerable groups.

There were many factors influencing the progress of the infection, particularly within the first wave. Even with lockdowns, the UK suffered tremendous losses of life. In hindsight, the infection rates in both the UK and USA were already at a tipping point once the lockdowns were adopted, and therefore too late to have maximum impact on the spread of the virus. This coupled with the population dynamics of the UK (high average age, high percentage of multi-person versus single-person households, high population density within regions of poor socioeconomics) all contributed to the poor outcome and higher deaths per capita compared with much of the rest of Europe.

But for Sweden, many experts now believe that with the country’s population dynamics, lockdowns would have saved many lives, particularly the most susceptible. Sweden’s decentralized approach to the pandemic also inhibited many actions to mitigate the spread of the virus through the population, and a lax approach to testing means that even now the true cost of Covid-19 to the Swedish population is not fully understood. This is in stark contrast to France for example, with a centralized government and strong mobilization of military and healthcare resources early in the pandemic (Yan et. al. 2020).

There is no one-size-fits-all strategy to deal with pandemics. Responses are shaped through various cultural and institutional factors that are different within every country. Preparedness for the next pandemic can only be enhanced by a retrospective analysis of the varying responses taken, in conjunction with various indicators such as geopolitical considerations, national healthcare capacity, and economics. Back in 2019, the Global Health Security Index (GHSI) had developed mechanisms to assess the preparedness of countries for epidemics and pandemics. Under their model, the UK and USA scored the highest, but both performed spectacularly poorly in response to Covid-19. So, what can we learn from this all? Well, preparedness is multifaceted; preparedness in terms of a country’s political leadership’s willingness to accept and act on scientific advice, and the strength of its’ society to work towards the greater good for all. This pandemic certainly highlighted the need for cross-border cooperation and planning for future epidemics/pandemics in terms of shared resources and joint initiatives, coupled with a positive impact of a strong infrastructure to offer citizens both social and economic security (Baum, 2021).


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