Vaccines against the flu and pneumonia are associated with a lower risk of developing Alzheimer’s disease, while infections are generally linked to increased mortality among people with dementia, according to three research studies presented at this year’s Alzheimer’s Association International Conference, which is being held virtually this week.
“With the COVID-19 pandemic, vaccines are at the forefront of public health discussions,” said Maria Carrillo, PhD, chief science officer at the Alzheimer’s Association. “This research, while early, calls for further studies in large, diverse clinical trials to inform whether vaccinations as a public health strategy decrease our risk for developing dementia as we age.”
Previous research had suggested an association between vaccines and protection against cognitive decline but no comprehensive study had specifically focused on a possible link between the flu vaccine and Alzheimer’s.
To address this gap, Albert Amran, a medical student at McGovern Medical School in Houston, and his colleagues searched 9,066 medical records for evidence of a possible link in their study, “Influenza Vaccination is associated with a reduced incidence of Alzheimer’s Disease.”
They found that people who consistently got their annual influenza or flu shot had a lower risk of developing Alzheimer’s. Their data revealed that the risk of Alzheimer’s inversely correlated with the consistency of flu shots — the more consistently people got their shots, the less likely they were to develop Alzheimer’s later. While a single injection translated to an approximately 17% reduction in Alzheimer’s risk, more frequent shots added another 13% reduction.
The researchers also observed that vaccines seemed to offer better protection when received at a younger age. For example, those who recorded their first vaccine at age 60 benefited more than those who recorded their first shot at 70.
“Our study suggests that regular use of a very accessible and relatively cheap intervention — the flu shot — may significantly reduce risk of Alzheimer’s dementia,” Amran said, in a conference press release. “More research is needed to explore the biological mechanism for this effect — why and how it works in the body — which is important as we explore effective preventive therapies for Alzheimer’s.”
Another team of researchers investigated whether existing vaccines could be repurposed for Alzheimer’s prevention in a study, titled “Repurposing of existing vaccines for personalized prevention of Alzheimer’s disease: Vaccination against pneumonia may reduce AD risk depending on genotype.” The team, led by Svetlana Ukraintseva, PhD, a professor of aging research at Duke University, discovered that receiving pneumococcal (pneumonia) vaccination between the ages of 65 and 75 reduced the risk of developing Alzheimer’s by 25%–30%, depending on individual genes.
Her team analyzed the risk of Alzheimer’s disease among 5,146 participants, 65 and older, from the Cardiovascular Health Study, who had received a pneumonia vaccination, either with or without an accompanying seasonal flu shot. They included a known genetic risk factor for early-onset Alzheimer’s in their analysis — that of a variant, or allele, in the TOMM40 gene, called the rs2075650 G allele.
They observed the largest reduction in Alzheimer’s risk (up to 40%) among people vaccinated against pneumonia, who did not carry the risk gene.
In a trend similar to that found by Amran’s group, the Duke team observed that Alzheimer’s risk declined with higher total numbers of vaccinations against pneumonia and the flu. In their study, however, the same effect for the flu shot alone was not evident.
“Vaccinations against pneumonia before age 75 may reduce Alzheimer’s risk later in life, depending on individual genotype,” Ukraintseva said. “These data suggest that pneumococcal vaccine may be a promising candidate for personalized Alzheimer’s prevention, particularly in non-carriers of certain risk genes.”
Finally, another research team discovered the risk of dying after infections was higher in people with dementia than those without dementia in their study, titled “Increased short- and long-term mortality following infections in dementia: A prospective nationwide and registry-based cohort study.”
Viral, bacterial, and other infections frequently occur alongside dementia, and these researchers wanted to understand whether such infections worsen dementia, make it more life-threatening, or even cause it.
Janet Janbek, a PhD student at the Danish Dementia Research Centre, and her colleagues used data from national health registries to study mortality in 1,496,436 Danish residents who were older than 65 and admitted to hospital with an infection.
They found that people who had dementia and visited the hospital for infections had a 6.5 times higher mortality rate than those without those conditions.
Patients with dementia or infection had a threefold higher mortality rate which was highest within the first 30 days after their hospital visit. Mortality rates remained higher for 10 years after the initial infection-related hospital visit for people with dementia.
The study also found that all infections, whether minor or life-threatening, increased mortality rates among those with dementia, compared to people without dementia or without an infection-related hospital visit.
“Our study suggests that the health care system — as well as relatives of people with dementia — should have increased awareness of people with dementia who get infections, so they get the medical care they need,” Janbek said. “People with dementia require more specialized treatment even when their hospital visits are not directly due to their dementia but to what might appear to be an unrelated infection.”
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