An October 2021 Israeli study showed the vaccinated were 9X more likely to be hospitalized than those who had natural immunity from prior infection.[i]
Weeks later the CDC released a contradictory study claiming those with natural immunity were more likely than the vaccinated to be hospitalized. As Martin Kulldorf, an epidemiological biostatistician from Harvard Medical School who analyzed the CDC study said, “Both studies cannot be right.”[ii]
More than 100 studies now show the effectiveness and longevity of prior COVID infections in preventing illness and hospitalization.[iii]
With the government’s push for vaccination mandates, the pressure was on the CDC to prove they worked better than natural immunity.
Their new study claims the Covid-recovered were 5X more likely than the vaccinated to contract Covid. Was everyone else wrong?[iv]
The study tells a different story.
First some background. The most accurate way to conduct a comparative study is to create two matched groups, one vaccinated and the other Covid-recovered and not vaccinated. Members in each group should be similar in age, lifestyle, and comorbidities, and adjustments made to match groups as closely as possible. Finally, with controls in place, study which group has the most Covid hospitalizations.
That is not what the CDC did.
Instead, they selected people hospitalized with Covid-like symptoms and accounted for age, but never properly adjusted for a broader range of covariates. When tested the CDC found 5% of the vaccinated and 9% of Covid-recovered were positive.
This appeared to be proof the government was right all along. Vaccines work better than natural immunity at preventing future Covid.
The media headlined the results and medical publications like MedPage, announced, “CDC: Prior Infection Won’t Protect You From COVID Hospitalization — Study shows importance of vaccination to prevent severe disease, even among previously infected.”
Sorry MedPage, the study only evaluated non-Covid hospitalizations and never addressed the previously infected.[v]
Here’s what the CDC did not say.
While fewer of the vaccinated in the study tested positive for Covid, it was not because the vaccine worked better, but because the two groups were so dissimilar.
- The vaccinated group contained older people with more Covid-like respiratory illnesses and more likely to be vaccinated.
- Conversely, the unvaccinated group consisted of younger patients, generally with fewer Covid-like illnesses and when hospitalized most likely had Covid. They were less likely to be vaccinated.
Since so many in the first group were prone to illnesses that appeared Covid-like, but not the actual disease, and were more likely to be vaccinated, it stood to reason they would have fewer actual Covid cases.
The CDC study never adjusts for older patients being frail with more Covid-like symptoms and more likely to be vaccinated; nor for younger active patients being more likely to be Covid recovered and unvaccinated. Even though the study’s’ own data shows this is a major contributing factor. 78% of the vaccinated are over age 65 and 55% of the Covid recovered are younger than 65.
Adjusting for these covariates would create radically different results.
Despite what the CDC implies, the study does not reveal if the vaccine provides better protection against future Covid than natural immunity. Rather, it tells whether vaccination or Covid-recovery is more related to actual Covid hospitalizations; or which of the two is more related to Covid-like hospitalizations.
The study never addresses whether the Covid recovered will benefit from the vaccine.
There are other shortcomings.
- The authors engaged 6004 vaccinated and 931 Covid-recovered patients for the study who tested negative, then adjusted these figures to arrive at the 5-fold increased risk for hospitalizations among the Covid recovered. “The paper does not report how many vaccinated and Covid-recovered people there are in the population at risk for hospitalization with Covid-like symptoms,” explains Kulldorff. Without these baseline numbers, it is impossible to know how widely, if at all the 931 to 6004 risk ratio applies.
- According to Kulldorff, another major discrepancy was that “96% of the vaccinated were hospitalized during the summer months of June to August, while 69% of the COVID recovered were hospitalized in the winter and spring months from January to May. Such unbalanced covariates are usually best adjusted for using matching as in them Israeli study.”
The CDC and media float figures from the study with little background or context. Yet any of the disclosures and matching adjustments the CDC study failed to make would dramatically affect the study’s results, perhaps bringing it more in line with the overwhelming number of studies proving the efficacy of natural immunity.
As for mandates, to date, there is no conclusive evidence that when considering the effectiveness of natural immunity and the benefits/risks of the vaccines, there is any legitimacy for requiring vaccines beyond the highest at-risk categories.