New Study Comparing Natural Immunity to the Vaccine

There was an interesting study out of Israel comparing natural immunity to vaccine-induced immunity for SARS-Cov-2. Generally it finds that natural immunity is more robust than vaccination, though the vaccine does still seem to yield some benefit to people with natural immunity. And it's not a small effect, we're talking seven-fold or thirteen-fold, depending on how you do the analysis. Note the three different comparisons:

Model 1 – previously infected vs. vaccinated individuals, with matching for time of first event

In model 1, we matched 16,215 persons in each group. Overall, demographic characteristics were similar between the groups, with some differences in their comorbidity profile (Table 1a).

During the follow-up period, 257 cases of SARS-CoV-2 infection were recorded, of which 238 occurred in the vaccinated group (breakthrough infections) and 19 in the previously infected group (reinfections). After adjusting for comorbidities, we found a statistically significant 13.06-fold (95% CI, 8.08 to 21.11) increased risk for breakthrough infection as opposed to reinfection (P<0.001).

Also:

Model 2 –previously infected vs. vaccinated individuals, without matching for time of first event

In model 2, we matched 46,035 persons in each of the groups (previously infected vs. vaccinated). Baseline characteristics of the groups are presented in Table 1a. Figure 1 demonstrates the timely distribution of the first infection in reinfected individuals.

When comparing the vaccinated individuals to those previously infected at any time (including during 2020), we found that throughout the follow-up period, 748 cases of SARS-CoV-2 infection were recorded, 640 of which were in the vaccinated group (breakthrough infections) and 108 in the previously infected group (reinfections). After adjusting for comorbidities, a 5.96-fold increased risk (95% CI, 4.85 to 7.33) increased risk for breakthrough infection as opposed to reinfection could be observed (P<0.001) (Table 3a).

Overall, 552 symptomatic cases of SARS-CoV-2 were recorded, 484 in the vaccinated group and 68 in the previously infected group. There was a 7.13-fold (95% CI, 5.51 to 9.21) increased risk for symptomatic breakthrough infection than symptomatic reinfection (Table 3b). COVID-19 related hospitalizations occurred in 4 and 21 of the reinfection and breakthrough infection groups, respectively. Vaccinated individuals had a 6.7-fold (95% CI, 1.99 to 22.56) increased to be admitted compared to recovered individuals.

 Finally, they compare vaccinated plus naturally immune to natural immunity only. 

Model 3 - previously infected vs. vaccinated and previously infected individuals

In model 3, we matched 14,029 persons. Baseline characteristics of the groups are presented in Table 1b. Examining previously infected individuals to those who were both previously infected and received a single dose of the vaccine, we found that the latter group had a significant 0.53-fold (95% CI, 0.3 to 0.92) (Table 4a) decreased risk for reinfection, as 20 had a positive RT-PCR test, compared to 37 in the previously infected and unvaccinated group. Symptomatic disease was present in 16 single dose vaccinees and in 23 of their unvaccinated counterparts.

I don't quite understand why they do the matching. Shouldn't they be able to use the full sample and do some statistical comparisons in terms of rates? Is the matching just a clever way to avoid doing fancy statistics? (And why not, assuming you have enough data anyway?)

This really piqued my interest, because I've been hearing quite a lot of nonsense dismissing natural immunity to covid. What I've heard ranges from wild speculation to non sequiturs to unscientific rejection of what we all know about the immune system.  (It tends to sound like, "Meh, we just don't know yet!" As if we couldn't analogize from other respiratory viruses, even other coronaviruses.) A lot of people have been playing the role of naïve empiricists this past year and a half, pretending we can't know anything without direct observation of the specific question at hand. We actually have some powerful general scientific principles that can be applied here. Some are from the logic of evolutionary theory (we all still believe in that, right?). Others are from a basic, high school level understanding of how the immune system functions (and a basic understanding of how the mRNA vaccines work). 

Here's my reaction: The paper's conclusion is exactly what we should have expected, at least directionally even if we can't predict the magnitude. The vaccines are scientific wonders, but the ones that are most common (the Pfizer and Moderna mRNA vaccines) are incredibly narrowly tailored. None of the live virus is present in the vaccine. It's just a strand of mRNA, basically some biological instructions that tell your cells to "make me some spike protein." This teaches your immune system to build antibodies for when the real thing comes along. I don't know exactly how pure the RNA sequence is in the vaccine, but I would guess that every strand of mRNA in a given formulation is making exactly the same spike protein. Don't get me wrong, this is great. It means when you do encounter the "novel coronavirus," it's not completely novel. Your immune system has some familiarity with what it's encountering and can fight it off, often without any hint of illness (though obviously we're now seeing a lot of breakthrough infections). But compare that to having a live virus replicating inside of you for weeks. In this latter case, your immune system isn't going to be narrowly tailored to one particular version of the spike protein. It's going to cue in on other pieces of the virus. If the spike protein mutates and you encounter this new strain of the coronavirus, that's okay, your immune system can recognize other signals that your body is being invaded and ramp up production of antibodies. Also, given the amount of exposure you have to the virus and its various proteins in the case of a live infection, you should expect that your body would spend more time and energy building up antibodies. I'm at the limits of my understanding of the immune system here, but I would suspect someone who just spent two weeks fighting off a live virus would have built up more antibodies than someone who's had two quick jabs of mRNA. 

See this Nature article explaining why the Delta variant is so much more transmissible:

Shi’s team and other groups have zeroed in on a mutation that alters a single amino acid in the SARS-CoV-2 spike protein — the viral molecule responsible for recognizing and invading cells. The change, which is called P681R and transforms a proline residue into an arginine, falls within an intensely studied region of the spike protein called the furin cleavage site.

Sometimes people forget, or pretend to forget, that evolution is a thing. Evolution isn't like organic chemistry or knowledge of the immune system, where you have to know how actual, specific biological systems work (T-cells and such). Evolution has its own simple, mathematical logic, absent of any specific details. (Though certainly the details enrich one's appreciation of the concept.) Given that there are replicators trying to pass their genes into the future, and given that those replicators vary from each other in ways that modify their probability of success, we should expect some versions of those replicators to proliferate and others to die off. If there is a mutant form of covid that is good at evading the mRNA vaccines (say, by having a mutant version of the spike protein), we should expect that mutant to proliferate. Maybe someone who knows more about this can contradict me. Perhaps the Delta variant's spike protein is no more likely to evade vaccine-induced immunity than the Alpha variants, it's just that the mutation makes it more infectious in general? But it does seem like we're creating a world that would select for mutant spike proteins. Biologists should be standing up and declaring that what's happening with the Delta variant isn't a surprise. 

All of this has me thinking, Why in the hell are we talking about a booster shot of the same vaccine that was developed in January of 2020? Given that someone was able to develop a working vaccine based on first principles basically on their first try, where is the vaccine that's tailored specifically to the Delta variant? The lesson coming out of this past year-and-a-half is that it's relatively easy to tailor an mRNA vaccine to a new virus. So let's have that lesson inform vaccination policy (including the approval process for new vaccines and vaccine recommendations from the CDC). If we're seeing evolution in the direction of altered spike proteins, let's have a more robust ecosystem of vaccines. How about, if you've already had the mRNA double-jab, the recommendation should be to get the Johnson & Johnson vaccine (which is not an mRNA vaccine). Or how about variolation? Let's see a proliferation of attenuated virus vaccines. The mRNA vaccines were a great way to buy some time and protect the most vulnerable individuals (at least temporarily), but we should expect a rapidly evolving virus to outfox it. I'd also like to see population-level serology sampling to determine the prevalence of antibodies, and furthermore to determine what kind of antibodies people are getting. Which proteins are our immune systems zeroing in on? And can we use this study of natural immunity to inform the development of vaccines? Can an mRNA vaccine hold the instructions for multiple proteins? Perhaps for multiple variants of multiple proteins? You know, so 180 million Americans (many times that number worldwide) are not all susceptible to a single mutation on a single protein. Even if you're still a total covid-hawk who viscerally rejects the notion of letting the virus run its course, the Israeli paper should be informing your opinion of what kinds of vaccines to pursue.

(By the way, it seems that Geert Vanden Bossche alerted us to this possibility. See his interview with Bret Weinstein here. I can't quite buy his conclusion that we shouldn't engage in a vaccination campaign during a pandemic, at least I think that's what he's saying. It's like saying "We shouldn't use this life-saving medicine because there's a finite supply that will eventually run out." I think the correct take-away is that we'll have to keep adjusting the mRNA vaccines to new variants, or eventually switch to attenuated virus vaccines.)

In the early months of the pandemic, I repeatedly heard commentators (covid hawks all) dismiss the idea that naturally occurring immunity could lead to herd immunity. The same people would often insist that we could only get there through vaccination. (See this incredibly bad-faith piece in the Atlantic, and my commentary on it here. ) It was thoroughly confusing. Say you had a society of people with enough vaccination coverage that it had herd immunity. These commentators were apparently saying that if you swapped out the vaccinated people for people with natural immunity, the virus would come back and start spreading again? Or perhaps they were simply saying that the concept of herd immunity arose in the context of a vaccination campaign. This is a historical claim about the origins of an idea, but it's completely irrelevant to the claim about whether herd immunity from natural infection would work. Or perhaps if asked directly they would have conceded that, yes, a sufficient level of natural immunity would provide herd immunity, but it would come at too great a cost along the way? Or as a matter of historical fact, it had never happened? (Though wouldn't it happen in this case, with covid being so infectious? And wouldn't it be fine if the non-vulnerable, who basically experience it as a mild flu or cold or as nothing at all, all got the virus while the vulnerable were being isolated and protected?) No version of the "herd-immunity-from-natural-immunity-wouldn't-work" claim actually makes much sense. I think these people were actually so confused that they themselves didn't even have a clear idea what they were claiming. They had so little patience for the notion of simply tolerating the virus that they shut off and began lobbing whatever rhetorical fodder was within reach. They were jack-knifing from one idea to another without acknowledging the change in direction. 

I can't help but feel a little vindicated by the study linked to at top (I'll happily retract that statement if the result doesn't hold up, though). A lot of people were suggesting that natural immunity to covid didn't exist at all, or was very short lived, or at any rate we couldn't count on it for protection. I knew this was nonsense at the time. If there were no natural immunity at all then sick individuals would simply never recover, they'd just keep getting re-infected by the virus circulating in their body. (Like, what model of the immune system did these people have? You will eventually fight off the viruses that are inside your body, as I think they would have conceded. But then you'd promptly be reinfected if new particles of exactly the same virus entered your body from the outside?) This was the dog that didn't bark, as in they would have been shouting from the rooftops if they found substantial numbers of reinfections. But reinfections were exceedingly rare. If the result of this study holds up, I'd like to hear some kind of correction from this crowd. A big, fat, blubbering apology to the Great Barrington Declaration crew would be in order. The greater robustness of natural immunity means their prescription is even more attractive. 

All those people who are saying they don't need the vaccine because they've already had covid aren't wrong. The Israeli study suggests they'd cut reinfection risk in half by getting vaccinated, but that's on top of immunity that's extremely robust. Most people would probably think it's sufficient and see no need to dredge the depths for tiny incremental amounts of covid protection. There is some finite risk of undiscovered dangers with the mRNA vaccines, which I discussed in my previous post. I personally don't care for this "unknown unknown" type of argument, and I don't think the VAERS data on reported vaccine side-effects is showing a real signal. But I can respect someone who has a different cost-benefit calculation than mine or who reads the evidence differently from me. I have far less respect for the condescending attitude of the vaccine scolds. "Just get the jab, you backwards rube! Learn about the science!" Clearly the cost-benefit calculus differs for different people. It depends on their risk factors; if you're in a high-infection-fatality-rate demographic you should get vaccinated. If not, it may not be worth it. I have just enough reservations that I'm not super-thrilled about my young children getting the jab. (BTW, it is the official position of the U.S. public health establishment that very young children shouldn't be vaccinated. According to the CDC, as of this writing the vaccines are only recommended for children above the age of 12. Even if that changes tomorrow, the current recommendation is completely defensible.) Given that vaccine-induced immunity is going to wane anyway, given that they're not going to get very sick from the virus, and given that they're likely to encounter the it eventually, it's probably best that they encounter the real bug and acquire robust immunity while young. It's unlikely that the vaccine is "protecting" them in that sense, just delaying their development of a truly robust immunity. 

The Israeli study is just one paper, so I don't want to put too much stake in it until someone replicates it. If it fails to hold up, maybe I'll leave the post up but just strike through a bunch of the above text. That being said some of the points I made above are independent of this particular study's results. There is no question that natural immunity is real and at least comparable to vaccine-induced immunity. That's a substantial update compared to what people were saying last year. 

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A further note on the matching, from the body of the paper. Here's regarding model 1:

These groups were matched in a 1:1 ratio by age, sex, GSA and time of first event. The first event (the preliminary exposure) was either the time of administration of the second dose of the vaccine or the time of documented  infection with SARS-CoV-2 (a positive RT-PCR test result), both occurring between January 1, 2021 and February 28, 2021.

And model 2:

Therefore, matching was done in a 1:1 ratio based on age, sex and GSA alone. Similar to the model 1, either event (vaccination or infection) had to occur by February 28, to allow for the 90-day interval.

I think this is a clever way to avoid having to run some kind of statistical model to adjust for different risks between groups. They could have done that, too, just for the sake of comparison. 

The experience of Sweden is instructive here. They eschewed strict lockdowns. We can infer that the virus was spreading through the population and a lot of people were developing natural immunity, and this all happened before the vaccine was widely available. They've mostly avoided this third wave of covid deaths. Some commentators have pointed out that Sweden compares unfavorably to its Nordic neighbors, but then again it compares quite favorably to Europe as a whole. 

Unknown Long Term Consequences

 I want to make a point about the topic everyone's worried about, but I don't want to unnecessarily freak anyone out. As in, if you've already gotten it and have suffered no lingering effects, you should probably not worry. But if you haven't gotten it yet, you might want to exercise additional caution due to the unknown long-term sequelae. Some have persisting complications, but most people appear to recover in fairly short order. Those appearances may be deceiving. There is simply no way to rule out severe long-term complications, because the long term hasn't arrived yet. The data needed to settle the question only exists in the future. 

I'm sure some of you see what I'm doing here. Re-read the above paragraph, but do a little Necker cube flip and pretend I'm talking about the vaccine instead of the virus (or vice versa if you read it the other way). I'm tuned in to media sources that are hyper-cautious about either the virus or the vaccine (yes, I consume media on both ends of the spectrum), often making this "unknown unknown" kind of argument. What surprises me is the symmetry. Evidence of harmful side-effects of the vaccine are pretty weak. Some people are making a big fuss about the VAERS (Vaccine Adverse Event Reporting System) dataset, which the CDC uses to collect information on adverse reactions to vaccines. Below is a screenshot. You can tell from the file sizes alone that there's something odd going on in 2021. We're getting an outsized number of reports, apparently due to the mass vaccination campaign.

Certainly someone should be looking into this. It's concerning, but it's easy to dismiss. In fact, I urge that we dismiss it by default until someone convinces us there's a real underlying signal in this noise. There are so many more people getting vaccines this year, and the age profile of those getting vaccinated skews older than what we've seen in typical years. There are simply far more opportunities for adverse health events to happen to someone who's recently gotten the poke (I should say, "to happen to happen to someone"), compared to previous years. This is naturally going to yield some spurious reports of vaccine reactions. I haven't done the analysis to say that this year's explosion in adverse vaccine events is plausibly attributable to spurious connections, but I think that it's safe to ignore this until a more thorough analysis suggests it's compelling. In other words, just as I don't think we should jump at every shadow, I don't think we should overreact to signals that are probably spurious.* We  should have some mechanism for dismissing such false alarms, not indulging costly counter-measures just because "they might be real."

That said, even if the "evidence" is convincingly explained away as noise, there will be people who cling to this "unknown unknown" alarmism. You technically can't disprove that there are unknown long term health effects. Even if negative outcomes don't manifest in the short term, they could show up later in life (say as a subtle but real increase in cancer or infertility or something). I think this is nuts. It's a Pascal's Mugging approach to risk management. "A problem exists because I claim it exists...oops it probably doesn't but let's entertain the very small risk that it does because it would be very bad if it does." Followed scrupulously, this leads us to spending all of the world's resources on mitigation for risks that aren't real. Let's have a real budget for mitigating tail risks, but let's keep that budget finite.

I would make the same argument for "long covid." When I first started hearing reports of long covid, they sounded like a vague smattering of very different symptoms that people can suffer from from a variety of reasons.** Brain fog (which I have often felt this past year and a half, but which I attribute to a dramatic change in my work environment and lifestyle). Lethargy (which I didn't experience, but which could likewise be caused by being home all day instead of going to the office...perhaps metabolic disorders from changes in physical activity and diet). Abnormal heart scans (which it turns out will show up in similar proportions in a random sample of people...that OSU study didn't even have a control group!). It reminded me of the observation that a doctor can look at an MRI for a back pain sufferer and attribute the pain to some abnormality (like a bulging disk), even though that abnormality is common in the healthy population not suffering any back problems. My reaction was to entertain the possibility, but to basically dismiss it as having any decision-weight. And I think that was the right call. (Here is a good piece on the topic by Adam Gaffney, which I riffed on here.) To be clear, there are people who have severe bouts of covid, who perhaps end up hospitalized, who survive but have some kind of permanent lingering effects from it. I've never doubted or denied that. But from early on I was calling bullshit on the notion that mild or asymptomatic infections were leading to serious long-term health problem. I'm not buying this "silent killer" view of long covid, that there is a huge amount of harm that's slipping under the radar, but poised to strike in the coming years and decades.***

Of course, someone could concede all the stuff from the Adam Gaffney piece. "Sure, most of those 'long haulers' didn't actually contract covid. Sure, there's a spurious signal, and a million ways to confuse noise for signal, so we should have been more cautious in raising the alarm. But...the long-term consequences are unknown! The long term isn't here yet!" 

Vaccine alarmists and long covid alarmists can both point to "evidence for" the thing they're worried about, and both can take refuge in this all-trumping appeal to unknown risks. I just want to point out the symmetry. I think the "long covid" alarmists are on slightly more solid ground in terms of the strength of their evidence. But the appeal to unknowable hazards is not dependent on and does not respond to evidence. 

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*Someone surely has a deep knowledge of the rates at which people experience adverse health events. It shouldn't be too hard to check the rates at which we're seeing adverse health events in the VAERS data. Who knows, maybe it's actually ten times as common as we'd expect. I heard someone give the anecdote of a man having a heart attack moments after getting his first shot of the covid vaccine. I'm sure that seems salient if it happens to you. But I'm just thinking, "Old people are having heart attacks all the time. Surely someone was going to have one in near proximity to getting their covid vaccine, and surely some alarmist is collecting these stories and broadcasting them."

**I feel a need to cite Scott Alexander's excellent recent piece on long covid. I think covid hawks could use his analysis to say, "See! Long covid is real!" And covid doves could use his analysis to say, "See! Long covid is way overblown! (Yes it's real, but that's not the point of contention.)" I think the long covid hawks are committing a logical fallacy that's a common advocacy technique: give a high-sounding number by using an inclusive definition that captures non-severe examples, then cite specific examples of the most severe cases. This is a way of insinuating that severe problems are more common than they really are. Alexander is overall more concerned about long covid than I am, but I want to applaud the very high quality of his approach. See this part commenting on a study of a large number of post-covid symptoms: "One flaw in this analysis is that it didn’t ask for premorbid functioning, so you can tell a story where unhealthy people are more likely to get COVID than healthy ones (maybe they’re stuck in crowded care homes? Maybe they put less effort into staying healthy in general?) But I don’t think this story is true - how come obviously plausibly COVID linked things (like smell problems) are significant, and obviously-not-COVID-linked things like diarrhea aren’t?" Emphasis mine. Also here: "An English team says there’s a Long COVID rate of 4.6% in kids. But there was a 1.7% rate of similar symptoms in the control group of kids who didn’t have COVID, so I think it would be fair to subtract that and end up with 2.9%. And even though the study started with 5000 children, so few of them got COVID, and so few of those got long COVID, that the 2.9% turns out to be about five kids. I don’t really want to update too much based on five kids, especially given the risk of recall bias..." Section 9, about post-viral symptoms for other common viruses, was particularly interesting. As in, "How common are mild carry-over syndromes in general?" Maybe these are just as common for typical cold and flu viruses, but we just don't notice them because they're less prevalent in normal times? Or we're inured to them because, like the viruses themselves, we've accepted them as part of the background risk of a normal life? We don't happen to associate them with a recent cold or flu because it doesn't occur to us that it might be the cause? 

***We've seen population level increases in death rates. What I haven't seen are population-level morbidity figures. I'd expect to see disease rates increasing for the population as a whole, with dramatic increases for younger populations. And the analysis should clearly separate out the effects of acute covid from long covid. The population-level spikes in mortality are noticeable. If long covid is real, and if it's as big a deal as some are claiming, the population-level spikes in morbidity should be out of this world. 

Mismeasuring Risk In Both Directions

Sometimes it's amusing to observe just how exaggerated are people's understanding of various problems. I once quizzed someone by asking them how much the earth has warmed since pre-industrial times. They said something like, "About 15 degrees." This is from an American context, so presumably they meant 15 degrees Fahrenheit. The real answer is more like 1.8 degrees. I don't know what kind of answer you'd get if you randomly polled people, but the subject of my non-random quiz is not alone in having an exaggerated sense of how much warming there has been. A literal "climate change denier" would be closer to the truth by saying zero. I've heard similar exaggerations for the amount of sea level rise that's expected in the coming century, citing a likely rise of several meters whereas it's likely to be in the tens of centimeters. (Larger projections exist in the literature, for sure, so you could cherry pick a large value and claim the mantle of "science." I've also heard outlandish projections of how soon Greenland's ice will be gone. Again, I don't know what a proper poll would show or how close it would be to the literature's best point estimate. But the catastrophic voices are louder than the moderates.) Again, someone saying "zero" would be closer to the truth than someone who says "six meters." 

I see the same phenomenon in estimating the threat posed by covid-19. Particularly when it comes to the threat it poses to young people, some of us (and I am including myself here) have been pointing out that the risk is very small. See this chart (which actually comes from an alarmist page, and which I cited in a recent post):

One could be forgiven for rounding the IFR for the 0-34 group down to zero and commenting that the risk is something that blends imperceptibly into the background of other hazards (like auto accidents and suicide). If I'm reading this chart correctly (partially gated), when polled, people in the under 34 group estimate themselves to have a 2% (!?!) chance of death conditional on contracting covid. (Original paper here.) There's something wrong when your risk calibration is off by a factor of 500. (That's 2% over 0.004%, but I should probably apply some kind of adjustment for the consideration that 18 and younger weren't represented in the polls. Even if I did that, there's no way their assessment of risk is anywhere near what it really is.) The institutions of public health should be absolutely ashamed that they've so thoroughly misinformed the public. A young person walking around thinking s/he's not at risk, as in a true "covid denier", is actually more correct than the misinformed young people captured in these poll numbers. 

(Unfortunately, it looks like the elderly are being irrational about their risk of covid in the other direction, saying that the mortality risk is lower than it actually is. In fact they see themselves as less at risk than the young people do. That said, their self perception of risk is way closer to the ground truth than the young people's.)

There may be some attempt to defend the catastrophic worldview by saying the grossly exaggerated values are stand-ins for expected values considering tail risk. Maybe they point to the right policies and mitigation responses, even though they're wildly off in terms of quantifying the problem? In other words, a few inches of sea level rise could actually be catastrophic, so we're best off thinking that this measure is much higher than it really is. Maybe 3℃ of global warning is really terrible, even if it sounds pretty mild. Maybe it's actually as bad as 10℃ sounds to the average person. Maybe the two or three orders of magnitude difference between the perceived risk of covid and the actual risk is a stand-in for some larger truth? Like, "Of course I'm not actually at risk, but I should act as though I am, lest I transmit the virus unknowingly to someone who's vulnerable." Or, "Considering the long-term effects of covid, I'm best off treating it as if it has a much higher mortality rate than it actually does." 

I think it would be astonishing if this misperception of reality just happened to give the right answer to some other question. It would be quite a surprise if overstating the degree of global warming by a factor of seven or eight yielded the correct policy positions. It's far more likely that people who are objectively wrong about measurable quantities are also wrong about the appropriate policy fixes (and here I mean public and private policy, as in government promulgated mask mandates and personal hygiene policies). We should certainly entertain tail risk and "unknown unknowns" when it comes to global hazards like covid-19 and global warming. But we shouldn't be misstating averages or inflating known quantities. Sure, simulate a scenario where 10% of young covid victims suffer "long covid," spell out the long-term costs in dollars, lost productivity, lost year of life, etc. Then weight that scenario with some kind of plausible probability estimate, which some third party could audit and critique. Don't fudge it by exaggerating the mortality risk by a factor of 100 or more. Maybe in some cases the tail risk is so compelling that it's worth extreme mitigation measures, even though the "average" scenario is pretty ho hum. We should be able to make that argument without distorting known quantities and misleading the general public. These distortions, which are common in catastrophic rhetoric, cede the intellectual high ground to the so-called "deniers." Deniers may have a simpler, dumber model of reality, but their error is usually bounded at zero. Mistakes made by catastrophizers, by contrast, often have no ceiling. 

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Then again, maybe we're just bad about thinking about risks in the 1% range. Maybe the young people in the surveys were basically giving an answer that sounded like a small number and mentally rounding down to zero, not realizing that a 2% risk of death is a pretty big deal. I recall Maia Szalavitz reporting that young people, when asked about quantitative hazards of drug use, tended to exaggerate by some huge factor (I think this was in her book Unbroken Brain). And yet they engage in drug use at much higher rates than their elders. That seems consistent with the exaggerated risks captured in the paper above. Still, there is something very wrong going on here. The public health establishment, if it's doing its job, should be correcting such hugely distorted perceptions, not leveraging them to make people do the right things for the wrong reasons. It should be telling young people that they can venture out and comingle with other young people (while still being cautious around the elderly and vulnerable).