New study finds small, temporary shingles risk after Covid booster shots

A large, peer‑reviewed study from the University of Groningen in the Netherlands analyzed electronic health records for more than two million people aged 12 and older who had received at least one Covid‑19 vaccine. The researchers found that the risk of developing shingles within 28 days of vaccination rose by about 7% overall, rising to roughly 21% after the third, booster dose of an mRNA vaccine. The authors stressed that the absolute increase in risk is small and that the study does not establish a causal link between vaccination and shingles.

The team separated vaccines by type, mRNA versus vector, and by brand. For individuals who received two doses less than 28 days apart, it was difficult to determine which vaccine contributed to the risk, so the primary analyses focused on those with a consistent vaccination regimen. The median age was 51, with most participants around the low to mid‑50s. The data showed that cardiovascular disease affected about 25.7% of participants and chronic lung disease about 16.3%. Pfizer/BioNTech accounted for about 69.2% of all doses, followed by Moderna at around 18.6%.

Within the study, the 28‑day risk increase was 7% when considering all doses, and 21% after a booster dose of an mRNA vaccine. Among men of all ages, the study found a significantly higher risk of shingles after receiving a vector‑based vaccine, with a 38% increase. The authors emphasized that these are relative increases and that most shingles cases identified in the study did not require hospitalization and were managed in primary care.

The authors described a possible mechanism: lymphocytes, a type of immune cell, can be temporarily depleted after vaccination, which may allow the varicella‑zoster virus to wake up. Repeated vaccine doses, particularly a third booster, might also temporarily reduce T‑cell activity, which helps control viruses that lie dormant in the body. The researchers stressed that the results show an association, not causation, and that replication in other populations is needed to confirm the finding.

The study noted mixed signals from other settings. Some Hong Kong data described a sharp rise in hospitalizations for shingles shortly after Pfizer/BioNTech vaccination, while a U.S. study using healthcare claims data found no increased risk after Covid vaccination, with vaccination not linked to a higher risk than flu shots. The authors highlighted that, in the broader context, shingles remains a treatable condition and that vaccines continue to provide substantial protection against Covid‑19.

The paper describes a three‑step approach: analyzing all vaccines together, then separating by vaccine type (mRNA vs vector) and by brand, and finally applying the same approach to specific dosing regimens when possible. The median age of participants was 51, and the population included a high prevalence of cardiovascular and pulmonary comorbidities. The most common vaccines were Pfizer/BioNTech and Moderna, with the former comprising about two‑thirds of doses administered in the dataset.

The study was published in Drug Safety on December 11 and analyzed data across a broad population, including multiple vaccination brands and regimens. The authors caution that the association is small and time‑limited, and they urge further research to determine whether any observed signal translates into meaningful clinical outcomes. They also underscore that the benefits of Covid vaccination remain substantial, including protection against severe disease and hospitalization.

The broader scientific conversation about shingles, dementia risk, and brain health continues to evolve. Some studies have suggested a link between shingles vaccination and reduced dementia risk in certain populations, while others have found no clear association. Medical experts emphasize that decisions about vaccination should consider the well‑established benefits of preventing Covid‑19 and shingles, not isolated signals from a single study.

Overall, the Groningen study contributes to ongoing surveillance of how immune responses to vaccines interact with latent viral reactivation. It does not change the fundamental public health guidance that Covid vaccines remain a critical tool in reducing Covid‑19 burden. As researchers explore these findings further, clinicians are encouraged to monitor patients for shingles symptoms within the initial weeks after vaccination and to discuss the relative risks and benefits of vaccination with patients on an individual basis.