In a powerful natural experiment with the help of Australian health data, researchers discovered that eligible for shingles vaccine can reduce the diagnoses of dementia, which can enhance the case for preventive strategies in the health of the brain.
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Published in a recent study in the Jama (The Journal of the American Medical Association)has determined an international team of researchers whether it is eligible for the vaccination of Herpes Zoster (HZ) (HZ) (virus that causes shingles) based on date of birth, the chance of receiving a new diagnosis of a dementia (memory loss and thinking problems).
Background
Dementia affects more than 55 million people worldwide and forms a growing crisis for public health. Although age remains the strongest risk factor, infections can also play a role. One underexposed link is between HZ and dementia. HZ The result of reactivation of the Varicella -Zosstervirus, a neurotropic virus that can influence the central nervous system. Vaccination against HZ can not only prevent shingles, but also lower dementia risk, possibly due to immune modulation. An earlier quasi experiment in Wales found this association, but replication is essential for different populations and health systems. Further research is needed to validate these findings worldwide.
About the study
The current study used a quasi-experimental design using first-line data from 65 general practices throughout Australia, facilitated by the Health Platform Pencs for Health Information. The analysis made use of a natural Cutoff created by the National Immunization Program, which on November 1, 2016 began to offer the live weakened HZ -vaccine (Zostavax) for free to persons aged 70 to 79 years. Being eligible was determined by date of birth: persons born on or after November 2, 1936 were eligible, while those who were previously born were not. This setup caused a comparison between groups that were almost identical in age and basic health, mainly different in vaccine access.
Patient records include diagnosis history, immunisations, recipes and demographic details. Birth dates were coded per week and all diagnoses, including dementia, were identified using open text fields provided by general practitioners. Patients aged 50 or older from November 1, 2016, and with at least one clinical visit between 1993 and 2024 were admitted.
The primary outcome was the first registered diagnosis of dementia for a follow-up period of 7.4 years. The most important exposure was eligible for HZ vaccination based on date of birth. Statistical analysis was aimed at Regression Discontinuity (RD), in which people were compared just before and after the suitability threshold. This method regulates both observed and non -evalued variables, based on no abrupt changes other than vaccination status. Secondary analyzes used time-to-event models, including accelerated failure time and Kaplan-Meier survival analyzes, together with robustness controls over multiple bandwidths and modeling strategies. All analyzes were performed using R -statist software.
It is important to note that the effect measured in this study is to be eligible for HZ vaccination, not for confirmed receipt of the vaccine, because the vaccination status is probably reported under the primary care data used. Because of this under -report, the study authors did not try to estimate the effect of actually receiving the vaccine, because this could overestimate the results.
Moreover, the research population came from practices that corresponded to participate and use the Pencs platform, so the data is not fully representative of all Australian primary care patients. The estimate of the effect is also ‘local’, most clearly applicable to people who were about 79 to 80 years old when the HZ vaccination program started.
The protective effect that has been observed in this study specifically relates to the living weakened HZ -vaccine (Zostavax), because the newer recombinant vaccine (Shingrix) was not used much in Australia during the study period.
Study results
Data from 101,219 patients were analyzed, aimed at 18,402 patients born within 482 weeks after November 2, 1936, eligible threshold. The average age in this subset was 77 years, with 54.3% of the participants women. The chance of receiving the HZ vaccine increased from 6.5% in the event of non-intended persons to 30.2% in the event of eligible individuals, which confirms that the date of birth rule effectively differentiated vaccine exposure.
It is important that no differences were observed in earlier health problems, admission of other preventive services or dementia risk factors about the suitability threshold, to support the validity of the natural experiment. Regression discontinuity analysis showed that the suitability for HZ vaccination led to a statistically significant reduction of 1.8 percentage point in the chance of receiving a new dementia diagnosis for 7.4 years (95% confidence interval: 0.4 to 3.3; p = 0.01). The protective effect was consistent in alternative follow-up duration, SRACE periods and model specifications.
Additional checks, including limited to frequent users of primary care and models for time-to-event, supported the primary findings. No effects were observed on other common diagnoses or preventive health behavior, indicating that the result was specific to dementia. Comparative RD with the help of an extra non -intelligent cohort yielded a comparable effect size of 1.5 percentage points. Kaplan-Meier-Plots and cumulative incidental curves also showed the delayed start of dementia for vaccine-intelligent individuals.
The study closed off by confirming that no other interventions used the same date-of-birth rule for birthworthiness and demonstrated that the effect was unique for the birth threshold of 1936. Analyzes that shift the threshold to nearby years showed no comparable effect, which further confirmed the causal interpretation.
It is also important to note that dementia diagnoses are considerably underweared in the analyzed primary line data. For example, only about 1.4% of patients older than 65 in the PENCS data set had a dementia diagnosis, compared to an estimated 8.4% prevalence in the general Australian population. This sub -diagnosis means that the observed absolute effect size may not fully reflect the impact of HZ vaccination on the risk of dementia among the broader population.
These findings, in combination with similar research from Wales, offer consistent and compelling evidence that HZ vaccination can help prevent or delay the start of dementia.
Conclusions
In summary, this study has shown that persons who are eligible for free HZ vaccination due to their date of birth had a considerably lower chance of being diagnosed during a follow-up period of 7.4 years. The use of a quasi-experimental design made a comparison possible between almost identical groups, minimizing confusion and offering stronger causal conclusion than traditional observational studies. These findings emphasize the potential for HZ vaccination to serve as a cheap intervention for dementia prevention. However, further studies in additional populations, as well as mechanistic and clinical research, are needed to investigate the biological paths, generalizability and policy implications of these promising results.