Singapore Experts Caution Against Overinterpretation of Oxford Vaccine-Dementia Study

A recent study conducted by researchers at the University of Oxford has sparked interest among medical professionals in Singapore due to its preliminary findings suggesting that certain vaccines may reduce the risk of dementia. However, local experts urge caution, emphasizing that the evidence is still too weak to influence clinical practices or patient decisions. Released in June 2023, the Oxford study analyzed health data from nearly 437,000 individuals in the United States. The findings indicate that individuals who received either the shingles vaccine, Shingrix, or the respiratory syncytial virus (RSV) vaccine, Arexvy, which both contain the AS01 adjuvant, experienced a lower risk of developing dementia within an 18-month period. Specifically, the RSV vaccine was associated with a 29% reduction in risk, while the shingles vaccine correlated with an 18% reduction.

Dr. Philip Yap, a senior consultant in geriatric medicine at Khoo Teck Puat Hospital and chair of Dementia Singapore, remarked, "It gives us a possible explanation that the secret recipe may lie in the adjuvant. The adjuvant is actually given in these recombinant vaccines to boost its efficacy. When you give an adjuvant, the vaccine is supposed to elicit a stronger immune response, like a booster."

Despite these promising findings, Dr. Yap and other specialists stress that the results should be interpreted with caution. Dr. Chong Yao Feng, a consultant in the neurology division at the National University Hospital, noted that while the study was well-executed, it is primarily epidemiological, relying on observational data rather than randomized controlled trials. "The nature of epidemiological studies is that they demonstrate associations but not causations, unlike randomized controlled trials," Dr. Chong explained. He expressed concern that the study could mislead patients and health authorities into prematurely adopting these vaccines for dementia prevention, stating, "We cannot repurpose shingles or RSV vaccines for dementia prevention on the basis of this study alone."

Dr. Zhao Yi Jing, a neurologist at Mount Elizabeth Hospital, echoed these sentiments, emphasizing the need for longer-term studies to assess the vaccines' effects on dementia, a condition that typically develops over several decades. She pointed out that the 18-month observation period is too short to draw definitive conclusions and added, "The pathological process of dementia can begin 10 to 20 years before clinical symptoms appear."

Moreover, Dr. Yap cautioned against the potential unintended consequences of enhanced immune responses, which might inadvertently provoke chronic inflammation while attempting to clear amyloid plaques—proteins associated with Alzheimer's disease. "You want to remove the bad amyloid, the toxic substances. But at the same time, you do not want damage to the good cells," Dr. Yap stated.

While the notion of vaccines playing a role in dementia prevention is intriguing, experts agree that current evidence remains insufficient. Dr. Zhao also highlighted that ethical and regulatory considerations are crucial when contemplating the repurposing of vaccines for new uses.

In light of these findings, medical professionals emphasize the importance of established methods for lowering dementia risk, including regular exercise, mental stimulation, and a balanced diet. Dr. Yap noted that preserving hearing and vision is increasingly recognized as essential, stating, "Hearing loss increases the risk of dementia by up to two times." He advised individuals with hearing impairments to consider hearing aids and to seek treatment for vision problems, such as cataracts, which can be addressed through low-risk surgical interventions.

As the discourse around vaccine efficacy continues, experts remain vigilant in their pursuit of evidence-based practices to combat dementia, reinforcing the need for further research and careful interpretation of emerging studies.