The report is a non-peer-reviewed preprint with several limitations. The authors themselves have recognized that this finding needs to be confirmed.
On December 20, 2022, U.S. Senator Rand Paul tweeted, "the higher the number of vaccines previously received, the higher the risk of contracting COVID-19." To support this claim, Paul posted a link to a study on medRxiv, a server that publishes preprints of scientific articles in the health sciences, titled "Effectiveness of the Coronavirus Disease 2019 (COVID-19) Bivalent Vaccine." As a preprint posted on December 19, 2022, it has not been peer-reviewed yet and should not be used to guide clinical practice.
The study sought to evaluate the effectiveness of a bivalent COVID-19 vaccine, an updated vaccine meant to counter variants of the coronavirus and the original strain of the virus. The study's subjects included 51,011 Cleveland Clinic employees working with the non-profit medical organization when the bivalent COVID vaccines first became available in September 2022. The employees who tested positive for COVID-19 were examined in the following weeks. The researchers evaluated the protection the employees received against the virus based on their previous COVID episodes and the number of prior vaccine doses received.
By the end of the study, 21 percent of the 51,011 employees had received a booster shot using a bivalent vaccine from Pfizer or Moderna. During its course, 5 percent of the employees got COVID-19. The researchers found that when they applied a multivariable analysis to the data (accounting for factors such as age, gender, previous vaccine doses, and previous infections), the bivalent vaccines were about 30 percent effective overall in preventing a COVID-19 infection in a time when Omicron was the predominant strain of the virus.
Senator Paul's claim comes from the Results section of the study, where the researchers noted that the "Risk of COVID-19 increased with time since the most recent prior COVID-19 episode and with the number of vaccine doses previously received." However, the claim is misleading, as it omits context that the researchers provide in the study.
One of the limitations that the researchers noted in their study was that those "who chose to receive the bivalent vaccine might have been more worried about infection and might have been more likely to get tested when they had symptoms, disproportionately detecting more incident infections among those who received the bivalent vaccine." The researchers cautioned that individuals with unrecognized prior infection could have been misclassified as previously uninfected, resulting in an underestimation of the vaccine's protective effect.
Logically wrote to the study's authors, who replied that it needed to be kept in mind that "the study was done in a younger, relatively healthy, healthcare employee population" and "included no children, very few older people individuals and likely few immunocompromised individuals." As a result, the researchers urged caution in generalizing the findings to the public.
Commenting on the claims that more vaccines increase the chances of getting COVID, the researchers said, "It is unclear at this time why this was observed and how it should be interpreted," and, adding crucially that "more research is needed to either confirm or refute this finding."
They also pointed out that this was not the only finding of the study. "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," they wrote. Their email also reiterated that vaccination "remains an important preventive measure against COVID-19, and it's important to study new vaccines as they are released. Vaccination is still the best way to prevent severe illness and hospitalization from COVID-19."
After reviewing the preprint, Dr. Suruchi Shukla, Assistant Professor of the Microbiology department at King George's Medical University Lucknow, spoke to Logically. She pointed out that the study's key conclusion was that when the prevalent strain of the virus is included in a bivalent vaccine, it offers modest protection from infection. "The bit which claims that the risk of COVID increased with the number of doses has been... taken out of context," she explained, reiterating that "The study clearly states that the vaccine reduced the chances of COVID by 30 percent."
A study conducted by the U.S. Centers for Disease Control and Prevention (CDC) found a similar rate of effectiveness for the bivalent vaccines, with no concerns raised about the safety of the bivalent or earlier vaccines. When the U.S. FDA approved the bivalent mRNA vaccines (meant to counter BA.4 and BA.5 subvariants of Omicron), it noted that this decision was based on the safety and effectiveness of the original vaccines, as well as clinical data of a bivalent vaccine to treat a previous Omicron lineage, and non-clinical data for a bivalent vaccine using the BA.4 and BA.5 Omicron lineages.
Given all the context that is necessary to examine the study, from the nature of the people assessed (young healthcare workers) to the unknown information regarding prior infections and other conditions, as well as the caution urged by the authors of the preprint, the study cannot be used to justify a blanket statement that taking COVID vaccines increases the risk of getting COVID-19.
The study is a non-peer-reviewed preprint with several limitations mentioned above, and the authors have themselves suggested its findings need to be confirmed. It would be misleading to say that receiving more COVID vaccines increases the risk of contracting coronavirus. Moreover, several peer-reviewed studies have proven the benefits and effectiveness of COVID vaccines. Therefore, we have rated the claim as misleading.
The COVID-19 pandemic has given rise to a lot of potentially dangerous misinformation. For reliable advice on COVID-19, including symptoms, prevention, and available treatment, please refer to the World Health Organization or your national healthcare authority.