August 12, 2020

expert reaction to a commentary on herd immunity in Sweden

A commentary piece, published in the Journal of the Royal Society of Medicine, discusses COVID-19 herd immunity in Sweden.

Dr Julian Tang, Honorary Associate Professor in Respiratory Sciences, University of Leicester, said:

“This is an interesting report though I note that no Swedish public health co-authors were involved.

“The data is a bit patchy, for example, no serology data is given from Finland and Norway in Table 2 – and the line for Denmark seems to have been included with the UK data – likely a formatting error.

“If we assume that what they show is what was available at the time of writing, and that it has been accurately mined from the references given, it appears that the seropositivity rate in Stockholm (17%, Sweden) with no drastic lockdown measures, is about the same as Gangelt (14%, Germany), London (17%, UK) and New York City/State (12.3-21.6%, USA) – during April-May.

“Unfortunately, it is difficult to completely contextualise this data in terms of interventions, as Table 3 does not show the interventions implemented for Gangelt, London or New York during this period, but from what we know from the contemporaneous media and other coverage, all these other locations had imposed some form of lockdown by end of March 2020.

“So, we might have expected that any increase in the number of infections and therefore herd immunity in Gangelt, London and New York would have been frozen during the lockdown, yet that for Stockholm would have continued to rise further. However, there are no additional serology results beyond April shown in this paper to compare and demonstrate this difference between the seropositivity rates between each of these locations into June/July 2020.

“So the data seems a bit disjointed, but maybe that was all that was available for data-mining at the time of writing this article.

“Yet, if we assume that the Norway and Finland seropositivity rates were similar at the time to that of Denmark (2%, April, Table 2), where similar levels of interventions had been implemented (Table 3), you may well end up with the COVID-19 mortality plots shown in Figure 1b. As these are shown up to the end of June 2020, these also imply that the seropositivity rates for Sweden would be much higher than Norway and Finland at that time, given the number of daily new COVID-19 deaths per million population shown (since the more severe infections are likely to produce seroconversion).

“Ideally, we would really need to see the SARS-CoV-2 IgG seropositivity rates for June/July 2020 to compare the current levels of herd immunity across all these locations.

“So the authors’ conclusion from their title: “Four months into the COVID-19 pandemic, Sweden’s prized herd immunity is nowhere in sight” may not be entirely accurate and a bit premature – because we have not seen and compared the updated seropositivity rates for June/July 2020 across these same locations – at least from what I can see presented in the paper.”

Dr Simon Clarke, Associate Professor of Cellular Microbiology at the University of Reading, said:

“Natural herd immunity, generated by letting Covid-19 sweep through a population, may have been an appealing notion to some because of the lack of a lockdown or curbs on people’s freedoms, but it was nothing more than an idea which lacked supporting data.  The Swedish experience of attempting to achieve this, compared to other Nordic countries responses, resulted in much higher numbers of infections and deaths per capita, in addition to a prolonged outbreak.  Moreover, far fewer Swedes than predicted generated antibodies to the coronavirus, suggesting the strategy failed to generate widespread protective immunity.  These findings should prove a salutary warning, that appealing concepts and theories require supporting data when people’s lives are at stake and should not be used to fit pre-conceived narratives.”

‘Four months into the COVID-19 pandemic, Sweden’s prized herd immunity is nowhere in sight’ by Worlowski et al was published in the Journal of the Royal Society of Medicine at 00:05 hrs (UK time) on Wednesday 12 August 2020.

All our previous output on this subject can be seen at this weblink: www.sciencemediacentre.org/tag/covid-19

Declared interests

None received.