Covid boosters linked to small, temporary increase in shingles risk, study finds

A new study from the University of Groningen in the Netherlands found a small, temporary increase in the risk of shingles in the weeks after Covid-19 vaccination. The analysis used electronic health records from more than two million people aged 12 and older who had received at least one Covid-19 vaccine. The researchers, whose work was published in Drug Safety on December 11, examined the period within 28 days after vaccination and found a rise in shingles diagnoses, though they cautioned the increase does not prove the vaccine causes shingles.

Overall, the study reported a 7% increase in the risk of developing herpes zoster, commonly known as shingles, within 28 days of vaccination when all doses were considered. The risk rose to 21% after the third dose, a booster, of an mRNA vaccine. The team then separated vaccines by type, with mRNA vaccines such as Pfizer/BioNTech and Moderna on one side and vector vaccines, like AstraZeneca or Johnson & Johnson, on the other. For some analyses, particularly when two doses were administered less than 28 days apart, it was difficult to attribute the effect to a specific vaccine, so only consistent regimens were included in the type- and brand-specific analyses. The median participant age was 51, and most fell within a 32-year span around the median. Among participants, cardiovascular disease and chronic lung disease were the two most common conditions, affecting about a quarter and one-sixth of the cohort, respectively. Pfizer/BioNTech accounted for roughly two-thirds of all doses, with Moderna making up about one-fifth.

The authors say the small, temporary rise in shingles risk could be related to immune changes around the time of vaccination. They suggest that important immune cells called lymphocytes can be temporarily depleted after vaccination, potentially allowing the varicella-zoster virus—the virus that causes shingles—to reactivate. Repeated vaccine doses, particularly a third booster, might also render T-cells less active for a short period. Importantly, the researchers emphasize that the study shows a correlation, not causation, and most shingles cases are managed in general practice rather than through hospitalization.

The finding comes amid broader questions about vaccine safety monitoring. Separately, experts highlighted a global patchwork of data on shingles risk after Covid vaccination. In Hong Kong, officials reported a sharp rise in shingles hospitalizations shortly after Pfizer/BioNTech vaccination, while a U.S. study using healthcare claims data found no increased risk after Covid vaccination and concluded vaccination was not linked to a higher risk than flu shots. The Groningen study conducted a three-step analysis, including consideration of unknown vaccine brands, to capture a wide range of vaccination experiences.

Public health discussions around potential regulatory actions have intensified since the study’s publication. The U.S. Food and Drug Administration is reportedly weighing the addition of a black box warning—the agency’s strongest warning—on Covid vaccines to highlight major risks. CNN cited two sources familiar with the matter, who spoke on condition of anonymity. In a black box warning, critical safety information appears at the top of drug labeling. Officials have not publicly announced the decision, and details about timing and phrasing remain under discussion.

Beyond the new study, researchers and policymakers are exploring links between shingles and dementia risk. A separate analysis published in April, spanning more than two decades, suggested that shingles could trigger early-onset dementia, with the greatest risk observed in people aged 50 to 65. In that Italian study, 132,986 adults aged 50 and older were recruited, and among 12,088 hospitalized with a shingles diagnosis, there was a two-fold increase in early dementia over one year in the most severe shingles group compared with other groups. In the new study, those findings provide context for ongoing scrutiny of how shingles and brain health may be connected over time.

The topic has entered public discourse in different formats. A Daily Mail opinion piece by former UK health minister Lord Bethell argued that shingles vaccines may reduce dementia risk and criticized the NHS for not providing easy access to Shingrix, the shingles vaccine. Bethell described his personal decision to pay privately for vaccination and urged expanding NHS eligibility and lowering the age threshold to improve prevention. He framed the conversation around the potential for vaccines to contribute to dementia prevention, while Alzheimer’s Society researchers cautioned that more evidence is needed to establish a causal protective effect. The group noted that while some studies show associations, definitive proof of dementia prevention from shingles vaccination does not yet exist, and a holistic approach to brain health remains essential.

Shingrix is approved for older adults in many health systems, including limited NHS access in the United Kingdom. Bethell’s account highlighted ongoing debates about how best to balance vaccine access, cost, and potential long-term brain health benefits. Public health experts emphasize that the shingles vaccine’s proven ability to prevent painful shingles episodes remains a clear benefit, and that any potential dementia-prevention effects would require rigorous, independent confirmation before policy changes are made. The balance for health systems remains clear: vaccines save lives by preventing immediate illnesses, while research continues on longer-term cognitive outcomes.

Health officials say that, for most people, the benefits of Covid vaccines—reduced risk of severe disease, hospitalization, and death—continue to outweigh potential small, temporary risks identified in observational studies. Individuals should discuss concerns with their clinicians, who can weigh personal risk factors, vaccination history, and local guidance. Further studies, including randomized analyses where feasible, are needed to clarify whether a true causal link exists between Covid vaccines and shingles, and how that risk may vary across age groups, sexes, and vaccine platforms. In the meantime, public health messaging remains focused on the substantial protection vaccines provide against Covid-19 while ongoing safety monitoring continues to detect and characterize any rare or transient effects.