Vaccinated People Not More Susceptible to COVID-19 Than Unvaccinated

In any case, Fox said there’s no good evidence that vaccinated or boosted people would be at higher risk than the unvaccinated, as some have claimed.

“There is evidence in the sense that you can see some places where crude rates of infection in the unvaccinated are lower than in the vaccinated,” he said. But, he added, that “is unadjusted data, so you can’t rely on it.”

The vaccines, then, are likely still helping a person avoid infection with the omicron variant, even if only a little bit, and for a short period of time. (That limited protection is one reason why no one should rely solely on vaccination if they don’t want to get infected.) The primary purpose of vaccination, though, is to prevent serious illness — and on that front, the data are overwhelmingly clear that vaccination is still quite effective.

“The data generally suggest something like 20-30% efficacy against infection in the omicron era. Not high,” Johns Hopkins University epidemiologist Dr. David Dowdy said in an email. “But protection against severe disease remains strong.”

Indeed, numerous studies have found that there is a small decline relative to earlier variants, but the level of protection against the worst outcomes remains high. CDC analyses, for instance, show that two doses of an mRNA vaccine reduce the risk of hospitalization by 64% four to six months after the last dose, with protection rising to 84% with a booster after the same amount of time. Protection is even higher in the first months following a shot and against critical illness and death.

“We shouldn’t be expecting vaccination to provide long-lasting protection against infection,” Dowdy said, noting that protection against infection seems to last only a few months. “But the data are very clear that people who have been vaccinated and boosted are at much lower risk of hospitalization and death.”

Misconstruing Raw Data

The incorrect notion that vaccinated and boosted people are more susceptible to COVID-19 than the unvaccinated often comes from a misunderstanding of raw data, which cannot be used to reach conclusions about vaccine effectiveness.

The Walgreens data that our readers wondered about, for example, related to higher positivity rates in the vaccinated and boosted people who showed up to pharmacies to be tested for COVID-19, compared with those who were unvaccinated.

The Gateway Pundit shared a screenshot of a Walgreens “COVID-19 Index” dashboard with such figures and declared the numbers “shocking.” The site proceeded to inaccurately interpret the data as showing “the vaccines are not working as advertised.”

But as Walgreens had previously explained on its dashboard — and later said in a more detailed report — the positivity rates are unadjusted and can “lead to misinterpretation.”

In a May 11 update report, the company’s analysts, in partnership with scientists at Aegis Sciences Corporation, the firm performing Walgreens’ PCR tests, dug into the data to explore the differences between the vaccinated and unvaccinated groups that could affect the likelihood of someone testing positive for COVID-19 on either a PCR or rapid test (although the dashboard only showed results for PCR tests).

The analysis identified several differences that could explain the lower probability of unvaccinated people testing positive than the vaccinated groups, including being less likely to report having had close contact with someone with COVID-19, less likely to live in a county with a higher positivity rate, and more likely to report a previous COVID-19 infection. “These patients who survived were likely to benefit from natural immunity which provides some protection against future infections, further lowering the reported positivity rate in the unvaccinated group,” the report authors wrote.

Unvaccinated people were also more likely to be weekly repeat testers, who are more likely to test negative because individuals are not testing because of symptoms or an exposure.

And when the positivity rates were calculated just for those with a previous coronavirus infection, unvaccinated people were “significantly more likely” to test positive than vaccinated people, according to the report. “This supports previous findings regarding the ‘super immunity’ for patients who received the COVID-19 vaccination and had a previous COVID-19 infection,” the authors wrote. “While natural immunity does offer some protection for unvaccinated patients, previous infection and vaccination combined offers even more robust protection.”

Along similar lines, the analysis found that among older adults, a majority of whom reported testing for travel, “unvaccinated patients had significantly higher positivity compared to those vaccinated.”

A Walgreens spokesperson emphasized the limitations of the data on its dashboard, which is raw and unadjusted, unless otherwise noted. “This contributes to the overall picture of COVID-19 spread in a timely manner, but cannot be used to reach vaccine efficacy conclusions,” she said in an email. “As noted on the COVID-19 Index, in order to draw these important conclusions the data must be analyzed to control for factors including, age, repeat testing, recent or direct exposure to COVID-19 and pre-existing conditions among others.”

Certainly, the ability of the omicron variant to evade immunity is one reason why the Walgreens positivity data changed over time and why more vaccinated people are getting infected than before. But again, it doesn’t mean that vaccinated people are actually more susceptible to infection than if they hadn’t been vaccinated.

“Over time, more people are getting vaccinated, but also more people who are unvaccinated have gotten sick – which provides some level of protection going forward. It’s also true that immunity from the vaccine (or infection) against repeat infection does not last for a long period of time,” Dowdy said. “So, since not that many people have been vaccinated in the last ~3 months, vaccinated people are, in many cases, getting infected at similar levels to those who have not been vaccinated. But looking at hospitalizations and deaths, it’s clear that vaccines are still highly effective.”

Experts we spoke with cautioned against overinterpreting raw data that compares the vaccinated with the unvaccinated without attempting to control for other differences between the populations.

“It is really important to remember that you can’t just look at trends of covid and vaccination and draw conclusions about the effect of the vaccine. The reason for this is that those who are vaccinated are not the same as those who are not,” Fox said.

One huge difference is age. The older you are, the more likely you are to be vaccinated — and older people are much more likely to get sick and get severely sick, Fox said. Behavior and prior infection are also different.

What we really want to know, Fox said, is “among 20 year olds, or among 50 year olds or among 80 year olds (and really within those, among those with the same levels of exposure to the virus – something very hard to adjust for), are you more likely to be infected (and hospitalized, etc.) if you are vaccinated or unvaccinated. And all the high quality studies show that the vaccinated have lower rates, not higher.”

Avnika Amin, an infectious disease epidemiologist and postdoctoral research fellow at Emory University, also said it was problematic to jump to conclusions when the unvaccinated and vaccinated groups “aren’t totally comparable.” There are differences in who might seek out a test, which has become even more complicated more recently with the rise of rapid tests, she said, which generally aren’t reported to public health authorities.

“We have a harder time getting accurate rates now than we did earlier in the pandemic,” she said in an interview.

Those who are vaccinated and boosted are more likely to be more vulnerable to the coronavirus to begin with, she noted, and a previously infected person could be less likely to get vaccinated, since they are more protected against another infection than someone who has neither been infected or vaccinated before.

The CDC has been posting rates of COVID-19 cases and deaths among the unvaccinated, vaccinated and boosted on its dashboard. The data is adjusted for age, but not for other factors.

For the month of March, the dashboard shows that for people 12 years and older, the unvaccinated were 1.9 times more likely to test positive and 17 times more likely to die than those who were vaccinated and boosted.

Amin, who doesn’t represent the CDC, but was co-first author on a Morbidity and Mortality Weekly Report publication reporting similar data when the omicron variant first emerged in the U.S., acknowledged that this data was “imperfect,” but said that age is “a pretty big thing to adjust for.”

“It’s not just that your risk, if you’re exposed, your risk of getting sick increases with age, it’s also that you’re more likely to have an immunocompromised condition as you get older, you’re more likely to have other things that can put you at risk for severe COVID,” she said.

But, she said, there’s a reason why the dashboard is plastered with footnotes warning visitors about the potential problems with the data. And instead of reading too much into little blips in the data, she recommended using the information as a surveillance tool.

“The better way to think about this is the early signal of whether or not we need to be concerned about vaccine protection and whether it’s changing over time, or if it’s waning, or if maybe a new variant is coming up,” she said of the dashboard. Then, she said, scientists can conduct well-designed studies to investigate further.

Editor’s note: SciCheck’s COVID-19/Vaccination Project is made possible by a grant from the Robert Wood Johnson Foundation. The foundation has no control over FactCheck.org’s editorial decisions, and the views expressed in our articles do not necessarily reflect the views of the foundation. The goal of the project is to increase exposure to accurate information about COVID-19 and vaccines, while decreasing the impact of misinformation.

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