Spinning the Science, CDC-Style

The minimum that should be expected from CDC is accurate and apolitical reporting on its COVID studies. When the CDC headlines a press release “New CDC Study: Vaccination Offers Higher Protection than Previous COVID-19 Infection”, one would expect that the study at least shows some evidence, even limited evidence, in support of the headline. But that would be expecting too much.

The argument for mandatory vaccination of people previously infected with COVID (giving them so-called natural immunity) would be a lot stronger if the best direct comparative evidence suggested that vaccine immunity provided significantly better protection than natural immunity, rather than the reverse. As of now, the best comparison of natural immunity vs vaccine-derived immunity is a large retrospective study out of Israel which matched the time period when immunity was obtained, and found that natural immunity appeared to be significantly stronger than vaccine-derived immunity. Numerous other studies, not matched for the timing of onset of immunity, have demonstrated that natural immunity appears to be at least as protective as the best of the vaccines.

Unfortunately, the lack of any solid evidence showing that natural immunity is worse than vaccine-provided immunity, particularly in working-age population, does not mean that the CDC hasn’t proclaimed that result from its position as the national authority on infectious disease. On August 6, 2021, the CDC issued a press release along with publication of a retrospective study which concluded that for a somewhat ambiguously matched group of hundreds of people in Kentucky, being unvaccinated was associated with 2.34 times the odds of reinfection compared with being fully vaccinated.

While the CDC headline (“Vaccination Offers Higher Protection than Previous COVID-19 Infection”) clearly presented the study as showing that vaccines provide greater protection against COVID than natural immunity, is that what the study really demonstrated? Apparently so, if you ask the Hospital Association, whose website declared: “CDC study confirms vaccination’s greater protection against COVID-19 compared to prior infection and natural immunity”. Quite clearly, the unbiased, objective, scientifically literate staff of the CDC and AHA are convinced that this study demonstrates that vaccines unambiguously provide better protection than natural immunity. That claim continues to be used without examination or skepticism by reporters, politicians, pundits, and policymakers. Let’s examine that claim, because it’s a whopper.

First, let me state that I don’t fault the authors of this particular study. They are not the ones who twisted the data and headlines. Their conclusions, which I’ll go into later, are reasonable.

Here’s how the study was conducted. The authors identified 246 people who were previously infected with COVID in Kentucky in 2020, and then were re-infected during a two-month period in 2021. The authors assessed the vaccine status of those individuals (based only on Kentucky vaccine records). They also identified two “controls” for each re-infected person from among the larger group of previously infected individuals who were not re-infected in 2021, and assessed the vaccine status of those individuals. Then they computed the percentage of re-infected people who had been vaccinated and compared it to the percentage of non-re-infected “controls” who had been vaccinated, leading to the conclusion that previously infected people who did not receive a vaccination were 2.34 times more likely to be re-infected.

In other words, if you had recovered from a COVID infection, and subsequently chose to get vaccinated rather than stay unvaccinated, you were more than twice as likely to avoid re-infection.

Now that sounds like a fairly impressive result: 2.34 times less likely to be infected with COVID. One could always quibble with the exact number (e.g., some of the “unvaccinated” may actually have been vaccinated outside of Kentucky, people who were vaccinated may have been less likely to go get tested for COVID), and the authors themselves discuss some of the limitations, but it is generally consistent with other studies. So let’s assume that 2.34x number is accurate. What does it mean?

Does that mean that vaccine immunity is greater than natural immunity? Does it confirm “vaccination’s greater protection against COVID-19 compared to prior infection and natural immunity”, as proclaimed by the AHA? No, not even close.

The study does not compare immunity from vaccination vs. natural immunity. The study did not look at a comparison group of vaccinated subjects who had not been previously infected with COVID. The PR staffs of the AHA and CDC might want that to be the conclusion, and that may be what they “concluded”, but it is not a conclusion based on the data.

Assuming the data are accurate, the conclusion that could be drawn is: if someone has natural immunity, then subsequent vaccination can provide enhanced protection. Which makes sense. In fact, the 2.34x figure is close to the roughly 2x boost observed by Gazit et al. in the Israeli study that I previously mentioned. In that study, people with natural immunity were 13 times less likely to be infected with COVID as people who received the Pfizer vaccine when time-matched. That said, the protection from natural immunity could be even further improved, by a factor of about two, by being vaccinated.

Vaccination clearly enhances the protection from COVID afforded by natural immunity. By the same token, if someone already has vaccine-derived immunity, subsequent vaccination (i.e., a booster shot) will also provide enhanced protection. That certainly is what policymakers and vaccine manufacturers are saying right now (get your third shot!), and early data overwhelmingly supports that claim.

While vaccination provides enhanced protection to people with natural immunity, that does not mean that vaccination therefore provides superior immunity. Here’s a simplified example - let’s consider sunburns and sunscreen.

Assume I want to compare two brands of SPF 50 sunscreen to see which one provides better protection, Coppertone or Neutrogena. Immunity protection with vaccines fades over time. The same is true for sunscreens. We’re all aware that sunscreen protection fades over the course of a day, or after immersion in water, so it probably wouldn’t surprise anyone to see that re-application (with any sunscreen) will probably reduce the likelihood of sunburn.

The CDC’s Kentucky study is analogous to looking at a group of 246 individuals who reported sunburns (that’s the same number as in the case group in the Kentucky study – I’ll use the exact same numbers all the way through to make this point). Assume all of these sunbathers initially used the Coppertone sunscreen. A total of 67 (27.2%) of the sunburn victims also applied Neutrogena later in the day. A control group of 492 individuals who did not get sunburns was also identified. All of them initially applied Coppertone, but 208 individuals from that group (42.3%) also applied Neutrogena at some point later in the day. Since more of the individuals who did not get sunburns applied supplemental Neutrogena, apparently that would be sufficient for the AHA and CDC to conclude that Neutrogena provides better protection than Coppertone.

Unfortunately, I am not making this up.

Somehow I think the good folks at Coppertone (and your average third grader) might point out the absurdity of that conclusion. They would justifiably argue that if you simply switched the order of Coppertone and Neutrogena in the study, the same logic (if that’s the right word) would then suggest that Coppertone is better.

Obviously, the study does not compare Coppertone and Neutrogena at all. Instead, it compares one administration of a protective treatment with two such administrations. Is there anyone out there who doesn’t think that reapplying sunscreen would provide at least some additional protection against sunburn?

So the conclusion drawn by our supposedly objective experts is wrong. But what are the right conclusions?

Let’s examine that 2.34x figure in another way. Assume it is correct, and that previously infected individuals are 2.34 times more likely to be re-infected with COVID if they did not supplement their natural immunity from previous infection with a vaccine. This study was conducted in the spring of 2021 before the Delta variant became the predominant variant of COVID, so it’s safe to assume that the effectiveness of the vaccine was close to the originally published 95% mark. So if the vaccine provide 95% relative protection against infection, what is 2.34 multiplied by the unprotected 5%? It’s about 12%, suggesting natural immunity alone would provide about 88% protection.

Now, to an objective observer, 88% protection against COVID seems like excellent protection! It’s obviously not as good as 95%, but it is much higher than is typically provided by vaccines such as the flu vaccine, and well above the COVID protection figures for the AstraZeneca, J&J, and Sinovac vaccines. Score one for natural immunity - shouldn’t that be the headline for the AHA and CDC?

Actually, it’s even better than that. Remember, the unvaccinated, previously infected individuals were 2.34 times more likely to get COVID than the group that was BOTH vaccinated and previously infected. That group is highly likely to have greater protection than the group of people on which clinical trials were performed, which comprised people who had no prior history of COVID. What if the “double protection” provides another factor of two of relative protection, which would bring 95% effectiveness up to 97.5% effectiveness? That would imply that natural immunity, while 2.34 times more susceptible to COVID than double protection, still would still provide roughly 93% relative protection vs. controls. Unfortunately, we don’t know the actual numbers, but I suspect this estimate would not have been far off the mark at the time of the study, which predated the widespread emergence of the Delta variant.

Accordingly, upon closer examination, it’s likely that this paper, which has been widely touted to show the insufficiency of natural immunity, actually demonstrates that the protection afforded by natural immunity appears to be extremely strong.

Note that the authors identified 246 subjects in Kentucky who were re-infected with COVID during these months in 2021 after having survived COVID infection in 2020, and there were over a quarter of a million people in Kentucky who were infected with COVID in 2020. Perhaps that puts these numbers in perspective. Not many people were reinfected.

The proper conclusion from this paper is: “Natural immunity provides excellent protection from re-infection, and that protection can be enhanced with vaccination”.

How did that simple conclusion somehow get distorted into the CDC and AHA headlines trumpeting the superiority of vaccines over natural immunity? Perhaps those organizations can provide the answer – I’m not sure whether propaganda or ineptitude is a better look for leading health organizations. Pravda or a Trabant.

Again, I’m not faulting the authors of the paper at all. They actually made a narrow and reasonable conclusion that: “To reduce their likelihood for future infection, all eligible persons should be offered COVID-19 vaccine, even those with previous SARS-CoV-2 infection.”

“Should be offered vaccine” is a world different than “must get vaccine”. One might restate the authors’ conclusion as: “Since vaccination offers increased protection from COVID even among people with natural immunity, it would be wrong to prevent previously infected people from being vaccinated. They should have the choice.”

That’s right. They should have the choice.