Does Prior Infection Convey More Immunity Than a COVID Vaccine?

A CDC study suggesting as much was pre-omicron and didn’t account for boosters.

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Recent viral social media posts from popular right-wing figures and websites have suggested that a recent Centers for Disease Control and Prevention study determined previous coronavirus infections offered greater protection against coronavirus than vaccination.

The CDC published a study on January 19, 2022, which examined COVID-19 cases and hospitalizations in California and New York from May to November 2021. It found that unvaccinated individuals with no previous COVID infection were at highest risk of catching coronavirus, and that while receiving the vaccine initially offered greater protection than having previously been infected by coronavirus, when the Delta variant became the predominant variant “persons who survived a previous infection had lower case rates than persons who were vaccinated alone.”

Contrary to what some of the posts suggest, however, the study does not contradict CDC guidance that vaccinations offered greater protection against the virus: It was only once the Delta variant became the most common strain in the United States that those with a previous COVID infection saw greater protection than the vaccinated. Past strains of COVID saw lower rates of infection among the vaccinated population than the previously infected population. The CDC has also cautioned against applying the findings of this study to the current Omicron variant, which scientists are still researching: It’s not yet clear how natural immunity and vaccine-induced immunity compare. Kristen Nordlund, a CDC public affairs officer, told The Dispatch Fact Check that “those findings only applied to the time of Delta.” 

A statement from the CDC notes that the study was also conducted before booster shots became widespread “and does not reflect the immunologic benefit of additional vaccine doses.” Comparing Delta immunity to Omicron immunity “would be like comparing apples and oranges,” a CDC epidemiologist told the Wall Street Journal.

If you have a claim you would like to see us fact check, please send us an email at factcheck@thedispatch.com. If you would like to suggest a correction to this piece or any other Dispatch article, please email corrections@thedispatch.com.

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  6. Avatar photo
    Jon Holmlund

    The argument for vaccination for most people is strong but it is deeply regrettable that NO attempt to account for natural immunity is included in policy making. Natural immunity matters, and the point is not to "go have a COVID party," but to pose questions about a mandate to get vaccinated on top of a prior infection.

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    Ben Connelly

    Omicron definitely threw a wrench in that. Lots of second-timers getting Omicron.

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  8. Philip Howard

    why does so much effort go into comparing vaccine and acquired immunity? It seems from the CDC graph that they are roughly similar and both much better than unvaccinated/unexposed. To me was a big “we’re almost out of the woods!” moment.

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    Ian Fillmore

    Complex and nuanced scientific questions like this do not lend themselves to fact checks. Let's keep the fact checks focused on things that are actually fact-checkable.

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    Xsearnold

    I'm looking over the actual study write-up on the CDC website and it appears from Table 1 that they have absolutely no data for New York hospitalizations during this period (unless they're trying to say there were no hospitalizations due to Covid in New York over this period). With regard to the CA data, the problem I see is with the relative sample sizes for each cohort.
    There were 10,737 hospitalizations among the 15,484,235 subjects who were vaccinated and had no previous diagnosis (0.07% or 0.7 per 1000 ppl). There were just 378 hospitalizations among the 1,370,782 subjects who were unvaccinated and had a previous diagnosis (0.03% or 0.3 per 1000 ppl). The problem here is two-fold:

    1. The vaccinated/no diagnosis cohort is over 11 times larger than the unvaccinated/prior diagnosis cohort. To make meaningful comparisons between these cohorts, one has to assume a linear project, i.e., that enlarging the second cohort by a factor of 11 would yield 11 times as many hospitalizations, and this is a dubious assumption.

    2. There's a significant "chunk" of people missing from that second cohort, namely, the number of people who were unvaccinated and had a previous diagnosis of Covid-19 but could not "participate" in this epidemiological study - because they had died from Covid!

    So, sure, maybe you have a slightly better chance of not being hospitalized with Covid if you're unvaccinated and have had a previous infection but studies have already shown that this immunity wanes over time (which is why we have boosters) and it's clear that the risk of severe infection - and death - is far higher for the unvaccinated.

    It should also be noted (as mentioned in the fact-check) that conducting a study over such a relatively short time period is not likely to produce conclusive results.

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