Vaccinated at Higher Risk of COVID-19 Infection: Studies

A health care worker prepares a dose of Pfizer BioNTech COVID-19 vaccine in a file image. (Ezra Acayan/Getty Images)

People who have received COVID-19 vaccines are more likely to get infected than those who are unvaccinated, according to two new studies.

In one paper (pdf), from Cleveland Clinic researchers, each successive dose heightened the incidence of infection. The lowest incidence was among the unvaccinated.

In the other study, researchers in Indiana found that vaccinated people had a higher incidence of infection when compared to unvaccinated people who have natural immunity, or protection from surviving an initial infection.

The studies are the latest to find low or even negative effectiveness against infection among the vaccinated. A growing number of experts are pointing to immune imprinting, or suggesting it could be a cause. The term refers to how an immune system can be locked in by exposure to an early version of a virus, thus hindering its response to mutated versions. The COVID-19 vaccines target only the original virus strain apart from the updated boosters, which target both that strain and the BA.4/BA.5 subvariants of the Omicron variant.

Old vaccines “may have trained the immune response to expect a specific narrow pre-omicron challenge; thus, the response was inferior when the actual challenge was an immune-evasive omicron subvariant,” Qatari researchers wrote in a recent paper (pdf), which found a booster dose lowered the protection against infection.

Cleveland Clinic Paper

In their paper, a preprint published by medRxiv, Cleveland Clinic researchers analyzed data from clinic employees to arrive at estimates of vaccine effectiveness. The retrospective cohort study looked at data from Sept. 12, when the new boosters became available, through Dec. 12.

Researchers not only found the updated vaccines provide poor protection, but the “unexpected” result that people who received more doses of either version of the shots had an increased risk of infection.

“A simplistic explanation might be that those who received more doses were more likely to be individuals at higher risk of COVID-19. A small proportion of individuals may have fit this description. However, the majority of subjects in this study were generally young individuals and all were eligible to have received at least 3 doses of vaccine by the study start date, and which they had every opportunity to do,” wrote the researchers, including Dr. Nabin Shrestha.

“Therefore, those who received fewer than 3 doses (>45% of individuals in the study) were not those ineligible to receive the vaccine, but those who chose not to follow the CDC’s recommendations on remaining updated with COVID-19 vaccination, and one could reasonably expect these individuals to have been more likely to have exhibited higher risk-taking behavior. Despite this, their risk of acquiring COVID-19 was lower than those who received a larger number of prior vaccine doses.”

The researchers noted that multiple other studies, including the Qatari paper, have offered similar results.

“We still have a lot to learn about protection from COVID-19 vaccination, and in addition to a vaccine’s effectiveness it is important to examine whether multiple vaccine doses given over time may not be having the beneficial effect that is generally assumed,” they said.

Researchers did not look at the effectiveness against severe illness or hospitalization.

No funding sources for the study were listed. Under “funding,” researchers listed, “none.”

“It’s important to note that the study was done in a younger, relatively healthy, healthcare employee population. It included no children, very few elderly individuals and likely few immunocompromised individuals. Therefore, we urge caution in generalizing the findings to the public, which can include different populations than was in this study,” a spokesperson for the clinic told The Epoch Times via email.

“The study found that the longer it has been since last exposure to the virus by infection or vaccination, the higher the risk of acquiring COVID-19. It also found that the higher the number of vaccine doses an individual previously received, the higher the risk of contracting COVID-19. It is unclear at this time why this was observed and how it should be interpreted, and more research is needed to either confirm or refute this finding. It’s important to note that this paper has not yet been peer reviewed.”

Colorized scanning electron micrograph of a cell (purple) infected with a variant strain of SARS-CoV-2 virus particles (pink), isolated from a patient sample. (NIAID via The Epoch Times)

Indiana Paper

The Indiana researchers, including Dr. Shaun Grannis of the Regenstrief Institute, combed statewide testing and vaccination data as well as medical records to match individuals to compare incidence of infection, emergency department visits, hospitalizations, and deaths. The observational study, which only included people aged 12 and older with at least one previously recorded health care encounter with the Indiana Network for Patient Care between Jan. 1, 2016, and early 2022, crunched data from between Nov. 29, 2020, and Feb. 9, 2022.

The researchers estimated the incidence of COVID-19 was higher among the vaccinated when compared with the unvaccinated but naturally immune. Six months after the index date—30 days after an initial infection or 30 days after a vaccination—the cumulative infection rate was 6.7 percent among the vaccinated and just 2.9 percent among the previously infected. The rate remained higher among the vaccinated in all age groups when the results were stratified by age.

“Interestingly, at least in the study population and at [the] time of this analysis, natural immunity appears more effective in preventing new infections, a finding that is also reported in an earlier observational study,” the researchers said, pointing to an April paper from Israeli researchers. They theorized that vaccinated people may be more likely to get tested for COVID-19, which would lead to vaccine effectiveness being underestimated.

The study also concluded that the vaccinated were better protected than the naturally immune against emergency department visits, hospitalizations, and mortality.

“The findings highlight the real-world benefits of vaccination and allude to the health consequences of SARS-CoV-2 after the initial exposure,” Grannis and his co-authors wrote.

The paper was published by the American Journal of Public Health, which is the publication of the American Public Health Association. No funding sources were listed.

Editor’s note: This story has been updated with a comment from the Cleveland Clinic.