Covid-19: Does Sweden have herd immunity?

At the beginning of August I wrote an article about my experiences working as an emergency physician in Stockholm, Sweden during the covid pandemic. For those who are unaware, Sweden never went in to full lockdown. Instead, the country imposed a partial lockdown that was almost entirely voluntary. People with office jobs were recommended to work from home, and people in general were recommended to avoid public transport unless necessary. Those who were over 70 years old, or who had serious underlying conditions, were recommended to limit social contacts.

The only forcible restriction imposed by the government from the start was a requirement that people not gather in groups of more than 50 at a time. After it became clear that covid was above all dangerous to people in nursing homes, an additional restriction was placed on nursing home visits. At no time has there been any requirement on people to wear face masks in public. Restaurants, cafés, hairdressers, and shops have stayed open throughout the pandemic. Pre-schools and schools for children up to the age of 16 have stayed open, while schools for children ages 16-19 switched to distance learning.

My personal experience is that people followed the voluntary restrictions pretty well at the beginning, but that they have become increasingly lax as time has gone on. As a personal example, my mother and my parents-in-law stayed locked up in their homes for the first six weeks or so of the pandemic. After that they couldn’t bear to be away from their grandchildren any longer.

In my earlier article in August, I mentioned that after an initial peak that lasted for a month or so, from March to April, visits to the Emergency Room due to covid had been declining continuously, and deaths in Sweden had dropped from over 100 a day at the peak in April, to around five per day in August.

At the point in August when I wrote that article, I hadn’t seen a single covid patient in over a month. I speculated that Sweden had developed herd immunity, since the huge and continuous drop was happening in spite of the fact that Sweden wasn’t really taking any serious measures to prevent spread of the infection.

So, how have things developed in the six weeks since that first article?

Well, as things stand now, I haven’t seen a single covid patient in the Emergency Room in over two and a half months. People have continued to become ever more relaxed in their behaviour, which is noticeable in increasing volumes in the Emergency Room. At the peak of the pandemic in April, I was seeing about half as many patients per shift as usual, probably because lots of people were afraid to go the ER for fear of catching covid. Now volumes are back to normal.

When I sit in the tube on the way to and from work, it is packed with people. Maybe one in a hundred people is choosing to wear a face mask in public. In Stockholm, life is largely back to normal. If you look at the front pages of the tabloids, on many days there isn’t a single mention of covid anywhere. As I write this (19th September 2020) the front pages of the two main tabloids have big spreads about arthritis and pensions. Apparently arthritis and pensions are currently more exciting than covid-19 in Sweden.

In spite of this relaxed attitude, the death rate has continued to drop. When I wrote the first article, I wrote that covid had killed under 6,000 people. How many people have died now, six weeks later? Actually, we’re still at under 6,000 deaths. On average, one to two people per day are dying of covid in Sweden at present, and that number continues to drop.

In the hospital where I work, there isn’t a single person currently being treated for covid. In fact, in the whole of Stockholm, a county with 2,4 million inhabitants, there are currently only 28 people being treated for covid in all the hospitals combined. At the peak, in April, that number was over 1,000. If 28 people are currently in hospital, out of 2,4 million who live in Stockholm, that means the odds of having a case of covid so severe that it requires in-hospital treatment are at the moment about one in 86,000.

Since March, the Emergency Room where I work has been divided in to a “covid” section and a “non-covid” section. Anyone with a fever, cough, or sore throat has ended up in the covid section, and we’ve been required to wear full personal protective equipment when interacting with patients in that section. Last Wednesday the hospital shut down the covid section. So few true cases of covid are coming through the Emergency Room that it no longer makes sense to have a separate section for covid.

What about the few formal restrictions that were imposed early in the pandemic? The restriction on visits to nursing homes is going to be lifted from October 1st. The older children, ages 16-19, who were engaging in distance learning during part of the spring, are now back in school, seeing each other and their teachers face to face. The Swedish public health authority has recommended that the government lift the restriction on gatherings from 50 people to 500 people.

When I wrote my first article, I engaged in speculation that the reason Sweden seemed to be developing herd immunity, in spite of the fact that only a minority had antibodies, was due to T-cells. Since I wrote that article, studies have appeared which support that argument. This is good, because T-cells tend to last longer than antibodies. In fact, studies of people who were infected with SARS-CoV-1 back in 2003 have found that they still have T-cells seventeen years after being infected. This suggests that immunity is long lasting, and probably explains why there have only been a handful of reported cases of re-infection with covid, even though the virus has spent the last nine months bouncing around the planet infecting many millions of people.

As to the handful of people who have been reported to have been re-infected. Almost all those cases have been completely asymptomatic. That is not a sign of waning immunity, as some claim. In fact it is the opposite. It shows that people develop a functioning immunity after the first infection, which allows them to fight off the second infection without ever developing any symptoms.

So, if Sweden already has herd immunity, what about other countries? How close are they to herd immunity? The places that have experienced a lot of covid infections, like England and Italy, have mortality curves that are very similar to Sweden’s, in spite of the fact that they went in to lockdown. My interpretation is that they went in to lockdown too late for it to have any noticeable impact on the spread of the disease. If that is the case, then they have likely also developed herd immunity by now. Which would make the ongoing lockdowns in those countries bizarre.

What about the vaccine? Will it arrive in time to make a difference? As I mentioned in my first article, lockdown only makes sense if you are willing to stay in lockdown until there is an effective vaccine. Otherwise you are merely postponing the inevitable. At the earliest, a vaccine will be widely available at some point in the middle of next year. How many governments are willing to keep their populations in lockdown until then? And what if the vaccine is only 30% effective? Or 50%? Will governments decide that is good enough for them to end lockdown? Or will they want to stay in lockdown until there is a vaccine that is at least 90% effective? How many years will that take?

So, to conclude: Covid is over in Sweden. We have herd immunity. Most likely, many other parts of the world do too, including England, Italy, and parts of the US, like New York. And the countries that have successfully contained the spread of the disease, like Germany, Denmark, New Zealand, and Australia, are going to have to stay in lockdown for at least another year, and possibly several years, if they don’t want to develop herd immunity the natural way.

You might also be interested in watching the interview I did with Sky News about covid-19 or reading my article about the role of vitamin D in treating covid-19.

I am rolling out a ton of new science-backed content over the coming months, including:

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Author: Sebastian Rushworth, M.D.

I am a practicing physician in Stockholm, Sweden. I studied medicine at Karolinska Institutet (home of the Nobel prize in medicine). My main interests are evidence based medicine, medical ethics, and medical history. Every day I get asked questions by my patients about health, diet, exercise, supplements, and medications. The purpose of this blog is to try to understand what the science says and to translate the science in to a format that non-scientists can understand.

106 thoughts on “Covid-19: Does Sweden have herd immunity?”

  1. The rise in cases is too great to be explained by testing. For example in the UK, since August 1, cases are up 730% while testing is up 178%, suggesting an actual rise in cases of 410%.

    Regarding T-cells, is it possible that some countries have higher pre-existing immunity because they have in the past experienced an immunity-inducing coronavirus?

    1. Hi JJ,
      I guess that is theoretically possible, but considering how infectious coronaviruses are, it seems unlikely that one would be constrained to a single country or a few countries. I think covid shows pretty well how quickly a reasonably infectious virus spreads to every country on the planet.

  2. Pig Latin: You don’t seem to have read or understood Dr. Rushworth’s explanation of innate immunity, which involves, in the main, a T-cell response. The majority of people, upon exposure to coronaviruses, show no antibody response because their innate immunity have neutralized the invader. The vaccination religion relies upon the development of antibodies (the adaptive immune system) in the vaccinated to determine efficacy. This is a major flaw. At 71 I have never had a cold of any consequence or flu at all in my adult life. I take good care of myself; thus my immune system is robust. One of my guiding principles is when the government says something about health or nutrition, I generally do the opposite.

  3. Hi Sebastian, You seems to be so far the most reasonable doctor I know. You may have some points where you might be false but over 80%, I consider right.
    We all agree that it is a pre-existing immunity in the population. But this not explain the big differences across man vs women and elderly vs children.
    We may assume that all those categories have been exposed in the past equally on coronaviruses. Not women more than men and not children more than the elderly.
    So, I consider that it is not just this pre-immunity, it’s something more.

    I suspect that it can be due to thymus capacity to stimulate T cell and those with a high degree of thymus atrophy are on higher risk on complications in COVID-19.
    We know that thymus atrophy occurs with age and after 60 years thymus works at 40% capacity and also WE KNOW male thymuses atrophying more rapidly than those of females and this would explain why men die twice than women in Covid-19. If will look on reports we see that man deaths on group age 50-59 is equal with women deaths from 60-69 age…and so.on.
    Furthermore, all comorbidity conditions listed in Covid-19 coexists with thymus atrophy. Only two examples: Atrophy of the thymus is one of the consequences of severe insulin deficiency and so on.;

    “Thymulin, a zinc-dependent enzyme that stimulates the development of T cells within the thymus, may be involved. Production of cytokines by mononuclear cells is also reduced by zinc deficiency. These effects can be of clinical significance.”
    The main symptom in Zinc deficiency – loss of or diminished smell and taste.

    I think that vitamin D has also a huge role in Thymus atrophy.
    What do you think?

  4. As I read some info herd immunity slowly grows about 4% per year for infection diseases. How in Sweden scientists calculated that population has achieved herd immunity? Give some scientific evidence, thank you!

    1. Hi Peter, I’ve never heard this claim before that herd immunity grows by 4% per year. Please provide a link so I can see what evidence it is based on. Herd immunity happens when a sufficient proportion of the population is immune, and happens at different rates for different infections.

  5. Two points:

    There is no dispute that SARS-CoV-2 was first carried into Europe from travellers out of Wuhan. It’s irrelevant if it was European travellers or Chinese travellers. If the strategy were to detect every single infected person in a country, to isolate and treat them – what is the endgame? Close the borders forever? Impose mandatory quarantines for arrivals forever? Yes, there are supposedly rapid antibody tests, but those, too, have false negatives, and as most international business hubs across Europe see hundreds of thousands of arrivals every single day even a 99.9% sensitivity in those rapid tests means that hundreds or thousands of new cases will be imported every day when considering the fact that the vast majority of the planet’s population is insufficiently vaccinated against pathogens that were eradicated in Europe decades ago and that it’s unreasonable to assume that all 8+ billion people on Earth would be vaccinated against COVID-19 at once.

    There is also the mathematical model of “Six degrees of separation” that’s disproving the notion, mostly peddled by politicians of which the vast majority has no meaningful background in engineering or mathematical fields, that somehow you could interrupt transmission chains without closing borders and cutting off whole regions. Further reading:

    To us in the field of mathematics and CS this has been a very frustrating time, seeing how naive politicians, journalists and assorted water carriers believe that somehow, without closing borders, you could force whole societies into locking down to such a degree that no path can be established anymore between an infection cluster and people who were never exposed to the SARS-CoV-2 pathogen before.

    From this also follows that the assumption that, somehow, the virus emerged in November or December 2019 in the population of Wuhan, then, somehow, made its host carriers not interact with their peers, and that, somehow, in January 2020, the virus made the hosts release the brakes and made them flood Europe and the American continent at once, is wrong and naive.

    A much sounder, scientific assumption would be that the virus was already spreading across the globe at the end of 2019, and that the “spike in cases” in mid-March was not the beginning of the pandemic but rather the end but that it appeared to be a spike because mass-testing was rolled out, and that the RT-PCR screening tests were rather detecting the tail of the pandemic and that the subsequent increase in testing was just amplifying the noise floor of the false-positive rate in the test system itself. This is not disproven by an increase of hospitalizations due to COVID-19 – even today people are hospitalized across Europe with severe diseases because they were not vaccinated and because an infected person was travelling to Europe spreading a pathogen that was thought to be eradicated in Europe. But the vast majority of Europeans is already immune against measles etc, and therefore won’t fall ill.

    As exemplified by the vast majority of SARS-CoV-2 “cases” who are asymptomatic – they are asymptomatic because the hosts are already immune, which doesn’t stop the RT-PCR screening kits from detecting harmless levels of live or dead virus RNA strands.

    I should note that the very definition of “immunity” in the clinical sense means that someone won’t fall ill from the pathogen, be it through previous exposure, vaccination, or because their immune system can fight off the pathogen on its own. Immunity means you won’t develop the disease, it doesn’t mean that the pathogen can’t enter your body. The alternate definition of immunity as peddled by politicians, journalists, and – sadly – quite a few virologists and epidemiologists is wrong, as are claims that nobody could be immune to SARS-CoV-2/COVID-19 because no vaccine exists.

    In other words, herd immunity has not only been reached in Sweden but across most societies. Claiming anything else is ignoring basic math.

    Bonus point:

    Think back to your school years, then try to think of all your school peers that went on to become politicians and journalists. How many excelled in math, or scientific classes in general? Fact is that across all OECD members, the vast majority of politicians and government members have a law degree or a degree in social “sciences”. I think it’s only fair to assume that 99% of political leaders across the OECD, and their hysterical amplifiers in the media, struggle with basic math and scientific methods.

  6. jj,your observation is incorrect. There is no public information (a) which RT-PCR screening kits were used for the tests, and (b) which amplification setting, in particular which cycle threshold (CT) was used. The positive rate can be easily increased, i.e. manipulated, by increasing the CT from 30 (the standard in most EU countries) to 40 or higher, which also happens to be the standard in the US, the country with the highest “spread of the killer virus”.

    A CT of 40 effectively means that a healthy, non-infected person who happens to pass through a room where a person was staying many hours earlier who was infected 4 weeks ago will have a “positive test result”. If we assume a constant factor of 2 in the exponential replication of the PCR, a CT of 40 means an amplification by 2 ** 40, i.e. a single dead virus that this person picked up from the air will be amplified by a factor of 1 trillion.

  7. Niko

    Your final comment about politicians and journalists is partially true. There has been an explosion of knowledge over the past fifty years. However, there has also been a dumbing down among students in various disciplines though perhaps less among engineers and physicists. The cleverest seem woeful deficient in logic and reasoning. This is even worse among political animals. Try to reason carefully with a politician or reporter and notice how often they pivot from the topic to a smokescreen or personal attack.

    While a mere language person, I understand what Douglas Altman, a professor of statistics in medicine at the University of Oxford, wrote in 1998
    “The majority of statistical analyses are performed by people with an inadequate understanding of statistical methods. They are then peer reviewed by people who are generally no more knowledgeable. Sadly, much research may benefit researchers rather more than patients, especially when it is carried out primarily as a ridiculous career necessity.”

    The late Professor Altman would, I think, be dismayed by the coronavirus statistical debacle today.

  8. Thanks Gary, so if i understand your argument it’s that you can have herd immunity despite having only a low percent of the population with antibodies (according to a pre-print only 6.8% of blood donors/pregnant women in Sweden have Covid-19 antibodies) because despite exposure, innate immunity has taken care of the virus.

    To me, this seems like an untestable hypothesis, one that contradicts what all infectious disease epidemiologists are saying.

  9. Igpay Atinlay, the same pattern has been observed in swine flu (2009) when first they was alarming and then discovered T-cell with strong response to swine flu. Herd immunity was reached very easily despite that many countries did not used vaccination.
    ” But by 2020 it seems that lesson had been forgotten.”

  10. Interesting hypothesis. The UK has low levels of zinc in our diet. Zinc is important for the thymus immune response. Could there be a link between zinc and the coronavirus in different countries? Does Spain and Italy also have low levels of zinc? I don’t know, it might be worth someone finding out.

  11. Philip, has been studied already but it is much silence over: “In conclusion, there is an urgent need to implement dietary recommendations for all populations at risk of zinc depletion. In addition, prompt implementation of zinc supplementation should be considered in high–risk groups for zinc deficiency. These preventive and nutritional intervention measures have the potential to improve antiviral immune response for COVID–19 as well as for any future viral outbreaks. Large–scale studies are urgently needed to investigate the role of micronutrients in antiviral immunity, particularly drug–micronutrient immunity interaction.”
    Here the entire article:

  12. Hi Sebastian, here is what says one of experts in my country;
    – How credible can this be, given that it has already been pointed out that COVID-19 has already mutated and its immunity to it is short-lived?

    – These statements are based on the antibodies that are detected. And the real immune response that lasts a long time is not the antibodies, but the so-called cellular immune response. This was also the reason when talking about the coronavirus, to hypothesize that the BCG vaccine affects how severely we suffer from COVID-19. This is almost completely confirmed because cellular immunity is stimulated in an appropriate way. Thus, it has a greater effect on viral stimulation. Here we have the same effect when in the past we have encountered a similar coronavirus circulating in our territories. Thus, it is likely that some people have developed immunity. If we take into account that we already have 4% group immunity, in general, in 10 years they are approximately 40%. But this is a bit speculative. In any case, we have a virus that is very similar to the current SARSCoV2, found in our country in 2008.

    Here is some articles:

    1. Hi Peter,
      Here’s a direct quote from the Atlantic article you link to:

      Effects like this—“selective depletion” of people who are more susceptible—can quickly decelerate a virus’s spread. When Gomes uses this sort of pattern to model the coronavirus’s spread, the compounding effects of heterogeneity seem to show that the onslaught of cases and deaths seen in initial spikes around the world are unlikely to happen a second time. Based on data from several countries in Europe, she said, her results show a herd-immunity threshold much lower than that of other models.

      “We just keep running the models, and it keeps coming back at less than 20 percent,” Gomes said. “It’s very striking.”

      What they say is that herd immunity is reached when 20% have antibodies. In Sweden 7% of the population had antibodies in June (compared with 0,5% in April. Most likely we’ve reached 20% by now (in Stockholm we definitely have), and we could easily be well beyond that by now. The most recent Swedish antibody data is at least three months old.

      I can’t find anything in either article about immunity developing at a fixed rate of 4% per year.

      As to the statement from one of the “experts” in your country, no-one knows how short lived immunity to covid is, but we definitely know it’s at least nine months, since large numbers of people aren’t getting re-infected yet.

  13. Dr. Rushworth: If you are correct, how come Sweden only needed under 600 deaths/million to achieve population (“herd’) immunity and yet England already has far more than that and the current death stats indicate that it’s nowhere near achieving it? Population density? Healthcare spare capacity? Diet? Alcohol consumption/smoking?

    1. Hi Arthur,
      Of course, as you point out, there are big differences between countries’ populations that could differences in the share of a population that needs to be immune for herd immunity to be reached. There are also differences between countries in terms of what is defined as a “covid” death, which can make the numbers seem bigger or smaller. Sweden currently has 575 deaths per million while the UK has 626, which isn’t a very big difference, and both countries have similar death curves, with deaths now having dropped to very low levels. The main risk factor for dying of covid, other than age, is obesity, so that might explain any difference.

  14. Ivan: not innate immunity, adaptive T-cell immunity which is not detected by antibody tests. It would be great if a test for T-cell immunity were developed.

  15. UK had 40 Covid-19 deaths yesterday, Sweden 0. That’s quite a big difference. Of course you can argue that the low absolute numbers make the current data unreliable.

    Thanks for suggesting obesity. I thought population density leading to higher mean initial viral loads might be the answer, as well as healthcare spare capacity – AFAIK no-one in Sweden was sent home, or left at home by ambulances, to die of Covid-19.

    1. UK population is seven times bigger than Sweden’s, so if it is at the same stage in the pandemic it should have seven times the number of deaths, which i think has roughly been the case if you look at average numbers for recent weeks.

  16. Hi Sebastian. Thanks for your information.I watch this VIDEO the other day and may be you would like to watch it. and may be you can share. People need to know the truth. Regards. Rosa.

  17. On the claim above that, allegedly, the number of positive test results in the UK had risen by 410%, here’s the official data:

    As of now the positive rate is at approx. 1.7%, i.e. at the noise floor level of the operational false-positive rate of the used RT-PCR tests. If there are any true COVID-19 infections in the UK at the moment then it’s, at most, countable by ICU admissions and clinical diagnoses of COVID-19. I highly doubt that there are actual COVID-19 patients being treated in the UK at the moment, considering that even Scotland has now closed their special Glasgow Nightingale Hospital.

  18. I think there are a lot of anti-epidemic measures in Sweden, as in many countries. We will see how would going next waves there.
    … In my country one oracul says – corona will stay at about 4 years, she rarely misses prediction 🙂

  19. Good point Niko, I was assuming that the criteria for a positive test have not changed. However I doubt that this has changed in all of the countries with ‘second waves’. Do you have any sources for the actual CT threshold used in various countries? (I’ll be impressed if you do — this type of useful data is so hard to find)

  20. Arthur, a few months ago the UK government halted reporting of “COVID-19 deaths” because it became known – not through introspection within government but through an Oxford study – that basically Public Health England had tracked every single positive test result in a database, and when that person died at any point later the death was attributed to COVID-19 instead of the actual cause. Considering that the vast majority of these fatalities were in cohorts within the last stretch of their life expectancy, and with severe comorbidity, it’s more than reasonable to assume that these people did not die from COVID-19 at all.

    Government promised to make changes, but never did, and still continue to use the same reporting system. So when “40 people die in the UK from COVID-19” on a single day, what it really means is that at some point in the past they tested positive, i.e. with a very high probability they received a false-positive test result, and now they died from something entirely unrelated.

    It should be noted that recently Matt Hancock was asked what the number of people was who were under 60 and had no comorbidity and who died “from COVID-19” in the past 6 months. He couldn’t give an answer, so the interviewer revealed the number: around 300. That’s, on average, 10 per week.

    So less than 1% of the public number of COVID-19 deaths were under 60 and had no comorbidity.

  21. MD/PhD to MD, you really should probably wait a year before being so celebratory and proclamatory. I’m not an expert in infectious disease or epidemiology (and you don’t appear to be either), but I’ll defer to those that are experts who are not so convinced as you.

    1. Hi Christopher,

      I’m not an epidemiologist, nor am I an infectious disease specialist. But I am a thinking person who draws conclusions from the evidence I see in front of me, and I have a good understanding of human biology, physiology, and pathology, which I think helps me to draw reasonable conclusions.

      And I would say that the evidence is pretty conclusive at this point. I have not heard the so-called experts, like Anthony Fauci, for example, provide any reasonable alternative explanations to the ones I provide. And there do seem to be highly respected epidemiologists who agree with me, like Johan Giesecke for example.

      Apart from that, I think it’s my responsibility as a doctor to speak out when I see political decisions being made that are harmful to people’s health. So that is what I am doing. If we always only deferred to the so-called experts at the top of their respective hierarchies, we’d probably still be bloodletting patients.

  22. Wisdom learned is priceless. A Geneticist Methylation Report ordered by an Oncologist Naturopath Doctor identified trace minerals and nutrients deficiency provided quantitative science. Vitamin D3 and Zinc were not solely deficient; sulfate was deficient. The frequency of infections lessened, cancers in remission after 5 years, and twice daily meditations make any pandemic more bearable.

  23. Lawrence: Interesting. There is no RDA for sulfur in the U.S., but Dr. Stephanie Seneff thinks there should be. She has written at length about the role and importance of sulphate, such as its ability to render lipophilic molecules like cholesterol and vitamin D hydrophilic as well.

  24. Hi Sebastian. I’m in a clinical discussion group that only accepts journal articles and I’d like to forward your position. Have you, or will you submit a preprint?
    Kind regards

  25. Further to my comment above that the pandemic is already over in large parts of Europe, Dr Mike Yeadon has now proven it for the UK:

    I believe at this point medical measures to counter the acute psychosis in high-risk groups, i.e. politicians and journalists, who seem to believe that there’s a pandemic that can only be fought with lockdowns, should be intensified, starting with declaring a number of government heads incompetent in the clinical sense.

    I’m being serious.

  26. Coming back 3 weeks later and it appears I cannot find my comment asking about your null hypothesis and your response. You noted that reaching 2-5 deaths per day would invalidate your assumptions. However, the comment appear to be deleted. As the numbers continue to increase, are you still confident in your hypothesis? Why would you delete the comment?


  27. Sebastian, I’d recommend to link this somewhere prominent, the latest official data from Sweden (in Swedish, but easy to understand):

    ICU admissions are basically flat, as are deaths. And as in the UK, there’s a question if ICU admissions are because of COVID-19, or if admissions are because of something entirely else, and the patients test positive after admission.

    Fun fact I just learned: The European Center for Disease Control is headquartered in Stockholm.

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