Originally published June 22, 2023 5:00 pm PDT
A recently published peer-reviewed study in the journal Open Forum Infectious Diseases has confirmed that the risk of contracting COVID-19 is higher among those who have received more COVID vaccines.
The study evaluated whether bivalent coronavirus vaccines—the Pfizer-BioNTech and Moderna formulations—could protect against the virus.
The risk of contracting the disease “varied by the number of COVID-19 vaccine doses previously received,” the study authors write. “The higher the number of vaccines previously received, the higher the risk of contracting COVID-19.”
The study analyzed 51,017 employees at the Cleveland Clinic Health System in Cleveland, Ohio who were working there when the bivalent COVID shot was introduced.
They looked at the total number of infections that occurred during the 26 weeks after vaccination.
8.7% of participants acquired COVID-19 during the almost six-month period.
The study also showed that the protection effectiveness of the Pfizer and Moderna vaccines was only 29% during the omicron BA.4 and BA.5 variant phases, 20% during the BQ-dominant phase, and 4% during the XBB-dominant phase.
The authors noted the strengths of their study, including its “large sample size” as well as its “conduct in a healthcare system where very early recognition of the critical importance of maintaining an effective workforce during the pandemic led to devotion of resources to provide an accurate accounting of who had COVID-19, when COVID-19 was diagnosed, who received a COVID-19 vaccine, and when.”
They also touted their study’s analysis of vaccine effectiveness being “determined in real time.”
The authors conclude by stressing that multiple COVID vaccine doses “may not be having the beneficial effect that is generally assumed.”
“We still have a lot to learn about protection from COVID-19 vaccination, and in addition to vaccine 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 write.
The confirmation of increasing infection risk with increasing number of prior COVID vaccinations “needs further study,” they conclude.
“Ours is not the only study to find a possible association with more prior vaccine doses and higher risk of COVID-19,” the researchers emphasized elsewhere.
They pointed to a study from Iceland that similarly discovered that the “probability of reinfection increased with time from the initial infection” and “was higher among persons who had received 2 or more doses compared with 1 dose or less of vaccine.”
They referenced another study that found “history of booster vaccination compromised protection against omicron reinfection.”
Yet another study demonstrated that “[t]here is no advantage to administering more than 1 dose of vaccine to previously infected persons.”
Despite these findings, the U.S. Centers for Disease Control and Prevention (CDC) recommends Americans “stay up to date with COVID-19 vaccines.”
The health agency currently pushes the following messaging:
- “everyone aged 6 years and older should get 1 updated Pfizer-BioNTech or Moderna COVID-19 vaccine to be up to date.”
- “People aged 65 years and older may get a 2nd dose of updated Pfizer-BioNTech or Moderna COVID-19 vaccine.”
- “People who are moderately or severely immunocompromised may get additional doses of updated Pfizer-BioNTech or Moderna COVID-19 vaccine.”
- “Children aged 6 months–5 years may need multiple doses of COVID-19 vaccine to be up to date, including at least 1 dose of updated Pfizer-BioNTech or Moderna COVID-19 vaccine, depending on the number of doses they’ve previously received and their age.”
Open Forum Infectious Diseases is an official journal of the Infectious Diseases Society of America (IDSA), a medical association that represents physicians, scientists, and other healthcare professionals who specialize in infectious diseases.
Read the full study below:
