Disclaimer: I am not a medical doctor and this is not medical advice. My goal is to empower you with information. I will not take a position on whether you should or should not get vaccinated. Please make this decision yourself, consulting sources you trust, including a caring health care professional. 

What provides better protection against COVID, natural immunity, or vaccination?

When asking this question, we should step back and ask why we are asking it.

I am not posing the question to ask whether we should go out and deliberately contract COVID. I believe, instead, we should protect ourselves from COVID.

The main reason we ask this question is because we want to know whether people who have already gotten COVID need to get vaccinated in order to obtain a similar level of immunity obtained by people who have gotten vaccinated but have never gotten infected. Stepping further back, there are two reasons we could be asking this:

  • If I've had COVID, can I make myself more immune than I already am by getting vaccinated?
  • If we assume that anyone who gets infected can spread COVID, do we need to force everyone who has had COVID already to get vaccinated so they can enter a public place, keep their job, or otherwise participate in society, to stop them from spreading it?

If we are asking this question for the first reason, then we want high-quality, well-controlled, cause-and-effect data. We want to have a strong idea of what the vaccine would do within us to boost our own immunity if we take it. We are after the biological fact of what it is doing.

If we are asking this question for the second reason, as in evaluating the rationale for vaccine mandates, we do not want highly controlled data. We want fully confounded data. We want to know if we take random people off the street, are those who have had COVID but haven't gotten vaccinated any more or less dangerous to be around than those who haven't had COVID but have gotten vaccinated? The bouncer at the restaurant isn't going to use some sophisticated statistical analysis and has no need to understand biology. The bouncer is trying to filter out the safe people from the dangerous people.

Let's try to tackle this from both perspectives.

How I Selected the Data

I searched pubmed, biorxiv, medrxiv, and SSRN for peer-reviewed papers and preprints* that compared the infection risk of unvaccinated people who have had COVID to vaccinated people who haven't had COVID. I excluded studies that looked just at antibodies, T cells, or other markers of immunity. Since none of these have been validated as predictors of infection risk across the populations we are concerned with (everyone who has or hasn't had COVID and everyone who has or hasn't been vaccinated), these can only help us explain what we observe in infection risk, or help us hypothesize something about infection risk. They don't actually tell us the infection risk. So I focused exlcusively on studies that tell us the difference in infection risk, and I found nine of them.

The Clinical Trials (Pre-Delta)

Although randomized controlled trials (RCTs) are the gold standard of cause-and-effect evidence, for our question even the RCTs are just observational studies. This is because the vaccine trials randomized vaccination, but didn't randomize previous COVID infection.

The two trials that reported infection risk for vaccination and previous infection separately were the Pfizer trial and the Astrazeneca trials. Both of them were done before the delta variant took hold, and both of them appear to have defined previous infection based simply on a baseline blood sample that tested positive for nucleocapsid antibodies. These are antibodies that you make to natural infection, but not to vaccination. In both cases, people only got PCR tests if they had COVID symptoms. So we can't separate out getting infected from becoming a symptomatic case.

In both cases, we have no idea how long before the trial the previous infections were. We just know that previously infected people were infected at some point during the pandemic. Many of the natural infections could have been 9-12 months old by the time people experienced subsequent infections. We also don't know how many of the natural infections were even strong enough for the people to notice they had them. We just know they tested positive for antibodies. In other words, these people may never have been sick.

In the Astrazeneca trials, where people were followed for an average of 3.4 months, the unvaccinated, never-infected placebo participants had a 1.7% risk of developing symptomatic COVID, while the risk was 0.8% in unvaccinated people with previous infection, and was 0.5% in those who were never infected but got vaccinated.

In the Pfizer trial, where a slight majority of people were followed for 4-6 months and most of the others were followed for less, the never-infected placebo participants had a 4.7% chance of becoming a symptomatic COVID case, the naturally infected had a 1.3% chance, and the never-infected vaccinated had a 0.5% chance. Those who had both natural infection and vaccination had a 0.4% chance.

These studies were not done to compare the relative effects of natural infection and vaccination. They were just done to test the effect of vaccination. Those who had evidence of previous infection were tracked primarily to exclude them from the main analysis. As such, they didn't perform stats on the protective effect of natural infection. The Pfizer trial did, however, do stats on the effect of vaccination within people who had evidence of natural infection, and it wasn't statistically significant.

Nevertheless, in these trials run by the vaccine manufacturers themselves, done prior to the delta variant taking hold, using nothing more than a blood test for antibodies as evidence of natural infection, where natural infections could have been 9-12 months old, natural immunity looks 53-72% effective at protecting against becoming a symptomatic COVID case, and being vaccinated on average 3-4 months ago looks 70-90% effective.

Pre-Delta Observational Studies

A number of observational studies were done prior to the delta variant taking hold:

  • Among staff in publicly funded hospitals within the UK when the alpha variant was dominant, the rollout of the Pfizer vaccine was studied for two months. Everyone got PCR tests every two weeks and previous infection status was taken from medical records based on a previous PCR or antibody test. The age of the natural immunity was unknown or unreported, but  the vaccinations were only up to two months old. For every 100,000 person-days,  the chance of a positive test was 20 with no immunity, 5 with Pfizer, 3 with natural immunity, and 2 with hybrid immunity (Pfizer and natural).  This suggests that a very recent Pfizer vaccine is 75% effective, an older case of natural immunity is 85% effective, and combining the two adds a little extra boost — at least over a two-month period.
  • In long-term care facilities in the UK during the alpha variant, where everyone was over 65 and the median age was 86, the rollout of Pfizer and Astrazeneca was observed over 3 months. People got tested every month, and were also tested if they got sick or if there was an outbreak. A positive PCR or antibody test was used to define natural infections. The age of the natural infections were unknown or unreported, but the vaccinations were no more than 3 months old. The vaccines reduced the risk of testing positive by 64%, while natural immunity reduced the risk by 88%. Adding a vaccine to natural immunity had no benefit, not even a trend toward a benefit. In this population, older natural immunity was almost 40% more effective than more recent vaccination.
  • In long-term care facilities within Spain, where everyone was over 65 and the mean age was 86, the rollout of Pfizer and Moderna (almost entirely, 99.8%, Pfizer) was studied over 2.5 months. Testing was done whenever anyone had symptoms, was considered at risk of exposure, or was new to the facility. In this study they wanted to separate the effect of natural immunity from the indirect effect of widespread vaccination, so they compared two different time periods: the protective effect of natural infection in mostly 2020 was compared to the protective effect of vaccination in 2021. The natural infections were on average 6 months old, while the vaccinations were only up to 2.5 months old. Per 100,000 person-days, the risk without immunity was 12.8, with vaccination was 5.4, and with natural immunity was 1.8. Combining vaccination and natural immunity brought this down to 1.13. While this shows a slight boost of the combination, the natural immunity alone is three times better than the vaccine.
  • In a preprint* covering the four-month rollout of Pfizer and Astrazeneca among the staff of a cancer center in Milan, Italy, the protective effect of the vaccine over the rollout was compared to the protective effect of natural infection over a previous 8-month period. During both periods, PCR testing was done at the beginning and end of the period, upon development of symptoms or a positive antibody test, after holidays, and, for doctors, every two weeks. The natural infections were up to 8 months old while the vaccinations were on average two months old. The infection rate among those with no immunity was 9.5%, and among vaccinated was 1.5%. Natural immunity looked better or worse than vaccination depending on what method of PCR testing was used. If they tested a single gene, the reinfection rate was 3%. But if they tested multiple genes, which is more reliable, the reinfection rate was less than 1%. Overall this study is not very good for forming conclusions, but older natural infection looks comparable to more recent vaccination.

These studies have the advantage of being done in real-world scenarios outside the control of the vaccine manufacturers. They all suggest that an older case of natural immunity is equal to or substantially better than a more recent vaccination, and they conflict as to whether adding a vaccination will make natural immunity even better.

A Study Covering the Whole of Israel

By far the largest study is a preprint* covering the entire country of Israel from June 1, 2020 to March 20, 2021. This covers the period when the alpha variant was dominant, when Pfizer was the exclusive vaccine used. PCR testing was free and generally ordered because someone was sick or was exposed to someone who was sick. Previous infections were 2-10 months old, and vaccinations were 0-3 months old. The more recent vaccination was 93% effective against infection, 94% against hospitalization, 94% against severe illness, and 94% against death. Older cases of natural immunity were 95% effective against infection, 94% against hospitalization, and 96% against severe illness.

Since only one single person in the entire country died of a second infection, the stats couldn't be done on natural immunity and death.

In by far the largest study, old natural immunity is shown to be equivalent to recent vaccination.

The Two Time-Matched Delta Studies

Two preprints* cover the time period when delta became dominant, which is important because delta may evade immunity from spike protein-based vaccines more effectively than natural immunity. These are also the only two studies in the entire batch that compare vaccinations and natural infections that happened at the same time. This is critical, because immunity of any type can wane over time, so we only appreciate the relative strength of each when they are equally fresh.

One was done in Israel, and the other in the United States. On the whole, the US study was designed to replicate the Israeli study by covering the same time period, focusing on the delta variant, and matching people according to their demographics, risk factors, and when they got infected or vaccinated. In both cases, previous infections were drawn from electronic medical records. In Israel, it was from the second-largest HMO. In the US, it was from the Veterans Health Administration. The main differences between the two studies is that the patients in the US study were older (on average 62 instead of 33-36), and that Israel used Pfizer whereas the US study used a combination of Pfizer and Moderna.

In the Israeli study, natural infection offered 13-fold better protection against infection, 27-fold better protection against developing symptoms, and 8-fold better protection against hospitalization.

When the Israeli study used a group that was twice as big but not matched for the time of vaccination or infection, natural immunity was 6-fold more protective against infection and 6.7-fold more protective against hospitalization. No one in the Israeli study died.

At first glance, the US study appears to suggest the vaccines work better than natural immunity for people over 65, but not for younger people. For seniors, they offered 66% lower risk of infection and hospitalization and 95% lower risk of death. However, the study covered June through August of 2021, and delta didn't reach close to 100% of infections until July and August. By August, natural immunity had become equivalent to Moderna and superior to Pfizer.

Their figures are not well explained, but they appear to represent, first, the data adjusted for time of natural infection or vaccination, demographics and risk factors, and then the unadjusted data. In the first figure, natural immunity (green) becomes equivalent to Moderna (red) and superior to Pfizer (blue) by August. In the second figure with the unadjusted data, natural immunity becomes superior to both by mid-July, and widens its superiority by August.

Vaccination vs Natural Immunity Delta

Hybrid Immunity

Studies conflict on whether vaccination and natural immunity combined offer some superior advantage. The Israeli delta study suggested that the combination might cut the risk of infection in half compared to having just natural immunity alone (as if 27-fold better protection against being a symptomatic case wasn't enough!)

When they looked at people vaccinated after previous infection, which is most relevant to the question of whether someone who has been infected already should get vaccinated, this additional benefit was not statistically significant, but it looked like a 40% lower risk.

Similarly, in the Pfizer trial, adding vaccination on top of natural infection looked like it provided a 60% further drop in infection risk, but wasn't statistically significant.

A CDC study (in MMWR, which is not peer-reviewed) done in Kentucky from May to June of this year found a statistically significant 43% lower risk of infection when vaccination was thrown on top of natural infection.

Conversely, a preprint* covering health care workers in India found that those with natural immunity prior to vaccination had an additional 74% reduction in risk of infection compared to those who were vaccinated and never infected.

Nevertheless, at least one study contradicts the hybrid immunity concept. As I noted above, in long-term care facilities in the UK there was no benefit of adding vaccination to natural infection. It's not just that it's not statistically significant. Supplementary table 5 shows that, with time from adding the vaccination, the relative risk compared to natural immunity alone swings up and down all over the place.

I also wonder about other types of hybrid immunity. For example, if we could know we have a certain amount of established immunity already, would relaxing our guard just a little get us more exposure to dead viral fragments on surfaces and to mini-boosts of exposure to the live virus that are below the minimum infectious dose? I realize that we need to learn a lot before we can define what is safe and what is dangerous here, but there seems to be a broad spectrum of hybrid immunity concepts that should be explored.

I also wonder whether vaccination after natural infection wouldn't narrow the immunity from a broader spectrum of targets more resilient to a rapidly changing variant landscape toward the original spike protein that is becoming less and less relevant to the COVID we face here and now as time goes on.

I can say nothing more except that hybrid immunity deserves much more study.

Conclusions

The only studies that make the vaccines look better than natural immunity are the vaccine trials, and a surface reading of the US delta study. Reading the US delta study carefully makes natural immunity begin to show its superiority as delta fully takes over. Every other study clearly shows that older natural immunity is equal to or superior to more recent vaccination. When natural infections and vaccinations occur at the same time in a fully delta-dominant environment, natural immunity appears to be superior. In the younger population of Israel it seems to be wildly superior to the Pfizer vaccine. In by far the largest study covering the entirety of Israel, old natural infection is every bit as good as recent vaccination against infection, symptomatic illness, and hospitalization.

The only reason we can't say that about death is because only one single person died of a second infection in the whole of Israel!

To answer the questions at the beginning:

  • Does someone with natural immunity need to get vaccinated to obtain equal immunity to the vaccinated around them?

Definitely not. Their immunity at worst is just as good.

  • Will they get even better immunity if they add vaccination?

They might, but the studies conflict.

  • Can I decide who to fire from their job, who to keep out of the gym, and who to keep out of the restaurant by considering people with natural immunity dangerous unless they've been vaccinated?

Definitely not! If anything is obvious pseudoscience, it is this.

These data show that simply having an antibody test or a previous PCR test is enough to show that, even when your infection is way older than someone else's vaccination, it is equal to or better in its protection. Not allowing a mere anti-nucleocapsid antibody test or any record of any positive PCR test to serve as equal proof of immunity to a vaccination card is scientifically unjustifiable.

Video With Q&A

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*Footnotes

*  The term “preprint” is often used in these articles. Preprints are studies destined for peer-reviewed journals that have yet to be peer-reviewed. Because COVID-19 is such a rapidly evolving disease and peer-review takes so long, most of the information circulating about the disease comes from preprints.

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23 Comments

  1. Chris, you mentioned the Kentucky study and sort of accepted it at face value. When I looked at it a few things stood out to me and I’m wondering if you see the same:

    1) The study was done while testing protocols for vaccinated and unvaccinated were different; both the cycle thresholds used in the PCR tests and the less unified but still (I suspect) impactful tendency for hospitals and doctors not to test vaccinated people for Covid as much as their unvaccinated counterparts. Both of those would have inflated the effectiveness of the naturally immune + vaccinated cohort vs the naturally immune + unvaccinated group when using “new Covid cases” as the endpoint.

    2) The study was done before Delta was established in the US.

    Also, and this isn’t just about the Kentucky study but…do all the natural immunity vs natural + vaccinated immunity studies use Covid Cases as the metric? I definitely can understand why they were doing that last spring but isn’t it kind of an outdated rubric at this point now that we’ve more-or-less given up on herd immunity?

    Finally, I wonder if it’s worth mentioning the studies that found a higher risk of adverse events in people who were infected with Covid-19 prior to vaccination for Covid-19. The two I know of aren’t great quality–both get their data from volunteers–but I also don’t see a reason why you’d see a difference in post-vaccine adverse events between infected then vaccinated vs just vaccinated folks if it wasn’t because the vaccine caused that difference. Here’s the larger and more official of the two studies, if you’re interested: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8078878/

    I’m truly curious if you see the same thing or not. I certainly haven’t read all there is to read on this topic.

  2. One of the best pieces I’ve read on this topic. As a person with natural immunity, I am closely following the studies with interest. Even though my COVID infection was a little more than a year ago, my SARS-CoV-2 Semi-Quant Total Ab just this month came back at 639.2 U/mL. I think my results are proof that protection through prior exposure is much more durable than originally speculated.

    I appreciate your summary of these findings and helping to put it in understandable terms.

  3. I DO appreciate your efforts on this.

    However, with all due respect, a perceptive 10 year old can see, and could see FROM THE START, that Covid-19 has nothing to do with real science (ie, it’s a crime against humanity political s c a m).

    We don’t need MORE and MORE clear obvious evidence of the clear obvious Covid SCAM of what has long been clear and obvious from the very start.

    The relentless focus on this new area of fraud or that new piece of information on the Covid scam going on every day in the alternative media is at this VERY LATE stage A COMPLETE WASTE OF TIME AND DISTRACTION from what everyone needs to immediately LEARN about to CONSTRUCTIVELY fight this obvious pseudoscientific Scamdemic, I mean how much MORE evidence do you need to see the obvious?  UNLESS people take it to the next level it’s just describing more in a slightly different way of the same obvious fraud….

    For people to GET to FIGHT against their destruction through Covid jabs they first need to have a proper grasp of the nature of the world they live in — they need to (want to) “see the light” first — because if they do they will be MOTIVATED to fight.

    The most vital urgent and DEEP understanding everyone needs to gain is that a network of psychopaths ARE governing big businesses (eg official medicine), nations and the world (the evidence is irrefutable) and that the Covid Scamdemic is a VERY DESTRUCTIVE WAR AGAINST NON-RULING PEOPLE EVERYWHERE — you and I. But that’s only ONE part of the equation that makes up the destructive human condition.

    It is NOT just a matter of “draining the swamp” at the top and we’re back to our former sick “normal.”

    The true, WHOLE, but “politically inconvenient” and “culturally forbidden” reality is more encompassing because “the swamp that needs draining” on a psychological and behavioral level is over 90% of people anywhere. Study “The 2 Married Pink Elephants In The Historical Room –The Holocaustal Covid-19 Coronavirus Madness: A Sociological Perspective  & Historical Assessment Of The Covid “Phenomenon”” by Rolf Hefti at https://www.rolf-hefti.com/covid-19-coronavirus.html

    Without a proper understanding, and full acknowledgment, of the true WHOLE problem and reality, no real constructive LASTING change is possible for humanity.

    Then … SPREAD THOSE DEEP TRUTHS FAR AND WIDE… and DO the RIGHT THING.

  4. A most excellent job. I am going to use this as the basis of a tabulate-graphical something or other I am still thinking about. Amazing work. We need our own wikipedia.

  5. Excellent summary in plain speak! Thank you Chris, you are a ‘master’ in your ability to teach this subject matter. Now I understand what my own position is and how to back it up, as well as being confident in sharing this information with my loved ones, who look to me for guidance. Thank you for sharing your expertise. MUCH APPRECIATED! 🎯❣️👍

  6. Well done Chris! Thanks so much! It’s basically what I’ve been reading and hearing from doctors, another PhD in nutrition and public health, the host and her guest doctors and scientific researchers at the Whistle Blower Newsroom, and the host of the Progressive Commentary Hour and his doctor guests and research scientists, all of whom believe in vaccination, but not if a person already has had covid or any other disease that has a or some vaccine(s) for it. Plenty of front line in the trenches doctors who have already treated hundreds of patients unlike “Dr” Fauci, who as far as they know hasn’t treated even 1 case of covid, and scientific researchers have written and said that getting vaccinated after having had covid can potentially cause health problems, even serious ones.

    1. I’ve also read and heard the same from Dr. Peter Breggin, Psychiatrist. He has had a archived pod cast for I would guess about a decade — The Peter Breggin Hour.

  7. I appreciate the measured analysis. Since major vaccination only got underway in the spring (at least here in the US), none of the studies cited here can yet address the effect of waning vaccination protection; we’re starting to see that the vaccine is only good for a few months, where older natural infections provide longer-lasting immunity.

    From the very beginning it bothered me that natural immunity has not been recognized. Cynically, I figure a lot of it is logistical; it’s harder to show an antibody test than it is to wave an official vaccine card. And there is always the pressure from financial interests (Big Pharma!)

    You directly address the question of getting vaccinated after a natural infection. Speaking for purely selfish reasons (having reluctantly been vaccinated in the spring), what I’m looking forward to is information about getting an infection after vaccination and if that might improve immunity. There’s speculation floating around about how the vaccines might suppress natural immunity through multiple avenues, but only time will tell.

    The immune system is incredibly complex, and has been fine-tuned over millions of years. Thinking we can bend it to our will is incredibly hubristic. Peter at Hyperlipid (a vaccine critic) commented recently about how vaccine passports might actually be a good thing – in an unexpected way. https://high-fat-nutrition.blogspot.com/2021/10/are-covid-19-vaccines-useful.html

  8. How is a 40-74% lower risk of reinfection when combining natural immunity and immunization “statistically insignificant”?

    1. Your question doesn’t make sense. Statistical significance cannot be determined from the size of a relative risk reduction alone.

  9. Wow, this is an amazing report. People need to read it and give it out to their docs, etc. Thanks for all of your hard work.

    1. Indeed, Suzanne I shall be printing it and sharing with my doctor soon when we start to discuss this topic. Also my local elected parliamentary representative. We are so very lucky to have discovered Chris.

  10. A healthy, normal weight, 49 year old friend of mine who had had covid in the beginning, died a couple of weeks ago. He never got vaccinated, because he thought natural immunity was enough. Not sure if I trust your deductive skills after reading this post.

    1. I’m very sorry to hear that, but I never anywhere said it is impossible to die from a second infection. There are hoards of people dying from breakthrough infections in UK and Israel who thought vaccination was enough. In the Israel-wide study covering up to the pre-delta period cited here, there was one person in the whole country who died of a second infection. I’m deeply sorry for your loss, but it doesn’t contradict the conclusions here.

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